The difference between people who claim that “houseplants hate me” and those who possess “green thumbs” is simple. Success with houseplants — or any other plants, for that matter — requires a basic understanding of the environments plants need to flourish, as well as respect for their talents and limitations. If you are one of the thousands (or perhaps millions) of people who have watched too many houseplants perish under your care, you need only to acquire some practical knowledge of how plants grow to change your brown thumb into a green one.
You will be wise to begin with plants that are easy to please, such as pothos, spider plant, or Swedish ivy, before advancing to more challenging houseplants. Yet even these and other “easy” plants need appropriate care based on a good understanding of their needs. This is the purpose of the following pages, in which topics relevant to thoughtful plant care are arranged alphabetically and discussed in detail. Use the information here to learn what plants need from their environments and from you. From choosing containers to troubleshooting pest problems, this section is intended not only to tell you what to do, but to explain why and how houseplants respond to the attention provided by their human keepers.
The gradual process of adapting to changing environmental conditions, such as light, temperature, or even wind, is called acclimatization. Plants can best adapt to changes when they are gradual rather than sudden. Plants that are moved outdoors in spring and brought back indoors in fall often need to be acclimatized to the attendant changes in light, temperature, and wind.
See also Fertilizer
Plant foods high in phosphorous are often preferred for blooming houseplants, because plenty of phosphorous (the middle number in the fertilizer analysis, printed on the label) supports plants’ efforts to produce buds and flowers. African violet fertilizers are the most widely available high-phosphorous houseplant foods; three popular African violet fertilizers have analyses of 1-3-2, 8-14-9, and 12-36-14. However, some African violet fertilizers are balanced, with equal amounts of the three major nutrients. When shopping for a high-phosphorous plant food, be sure to read the label.
Almost 300 years ago, a Swedish botanist named Carl Linnaeus (1707–1778) came up with the idea of giving plants Latin names consisting of two words, representing the plant’s genus and species. In his lifetime, Linnaeus managed to classify and name 7,700 plants, and the process he began continues today. Botanical names are used worldwide, so they comprise a universal language of plants.
One way to understand botanical names is to think of them as English proper names in which the last name comes first. For example, “Jones, John,” tells you that the person is a Jones (a large, somewhat similar group of people), but that he is the specific guy known as John. In parallel form, Ficus identifies a plant as a member of the genus that includes figs, and benjamina — the species name — clarifies that the plant in question is weeping fig. A third, nonitalicized word in single quotes in a botanical name is the variety name, for example, Ficus benjamina ‘Starlight’. An × within a botanical name tells you that the plant is a hybrid created by crossing different species. Some hybrids are so complex that no attempt is made to identify their species. This is often the situation with hybrid orchids, tulips, and many other flowering plants that have long, complicated pedigrees.
Botanical names are useful if you do additional research on a favorite houseplant, or if you plan to shop for a certain plant you want to add to your collection. The pronunciation of botanical names is often variable, which is not surprising when you consider that Latin, the language of the Roman Empire, is considered “dormant,” and is rarely spoken outside religious and scientific circles. The pronunciations given in this book are commonly used, but it’s important to realize that there is no absolute right or wrong where pronunciation is concerned. Regardless of pronunciation, you can depend on botanical names to accurately identify specific plants.
Beyond regular grooming, one of the simplest ways to improve the appearance of your plants is to keep them clean. Like other indoor surfaces, plant leaves often collect dust, though they also filter dust from the air through their transpiration processes. Removing this dust helps the plants by improving photosynthesis and transpiration. Once-popular leafshine products make leaves extra glossy, but, like dust, they can block the leaf pores, making it difficult for plants to exchange gases and release moisture. Instead of using commercial waxes, try using a half-and-half mixture of milk and water to bring out the sheen in naturally shiny plant leaves.
Wait until after your plants are clean and dry to wipe containers with a soapy cloth to remove dirt and fingerprints. This is also a good time to rinse out drainage trays — the final step in giving your entire indoor garden an orderly facelift.
Fine-foliaged plants. Plants with finer foliage can be cleaned with a gentle spray of water. In summer, it is usually easiest to take plants outdoors, set them in a shady spot, and spray them from all sides with a very fine spray of water. (If the pots need to be leached to remove excess salts, both tasks can be accomplished at the same time.) To allow time for especially nasty deposits of dirt to soften, wait 10 minutes or so after the first shower and then spray plants again. Gently shake off water and allow the plants to dry in a place protected from strong sun before returning them to their usual place.
If you must clean plants indoors, you can invite them into your shower or set them in a bathtub or sink and clean them with water from a spray bottle. Direct spray from a bathroom shower is often too harsh for houseplants, so the spray bottle method is usually best. Adding a few drops of dishwashing liquid to a quart of water in the spray bottle helps loosen dirt and dust so it floats off easily. Be sure to rinse cleaned plants well with lukewarm water before shaking off water droplets and returning plants to their places.
To clean the foliage of plants with hairy or finely cut leaves, tape a plastic produce bag over the pot and soil, then swish the foliage in a pan of warm water. It helps to loosen the dirt if you mix a few drops of dishwashing liquid into the water.
With some plants, such as ferns or others with fine leaf hairs that trap dust (velvet plant [Gynura] and piggy-back plant [Tolmiea] are two examples), you may want to submerge the foliage in warm, soapy water to get them clean. To avoid unnecessary mess, enclose the container and the base of the plant in a plastic bag, firmly taped in place. Fill a deep sink with lukewarm water with a small amount of dishwashing liquid added, and hold the plant upside-down while swishing it through the water. Allow the plant to drip dry before shifting it back into bright light.
Hairy-leafed plants. African violets and other plants with hairy leaves can be submerged, or you can use a soft paintbrush to sweep dust and debris from the leaves. African violets and some other hairy-leafed plants will develop leaf spots if water droplets do not dry promptly, or if the plant is exposed to bright sunlight while the leaves are wet. After cleaning, shake off excess moisture and turn on a gentle fan, which will circulate air and speed drying time.
Cacti. To clean spiny cacti, use a cotton swab to remove dirt and dust that persists after the plants have been sprayed with water.
To prevent bruising of leaves, and to do a better job of cleaning leaf crevices, support the back of a leaf with one hand while sponging or wiping the other side. Be sure to clean both sides, because many pests hide on leaf undersides.
Large-leafed plants. Although it’s a slow process, the best way to clean large-leafed plants is to do it by hand, one leaf at a time. Use a soft cloth or sponge and a pail of warm, soapy water, and support one side of the leaf with one hand while you wipe over the surface with the other. Clean both the top and undersides of each leaf. Along with dust and dirt, you may find yourself wiping up light infestations of spider mites and other tiny insects from leaf undersides. Don’t hurry, because this can be a very enjoyable chore that gives amazing results. Scientists have pointed out that such intimate contact between plants and their keepers benefits both parties. As you gently work them over, your plants are bathed in your breath, which is rich in the carbon dioxide they crave.
See also Interiorscaping, Repotting, Soil, Terrariums
The containers you choose for your houseplants are the only home they know, but they are part of your home, too. This balancing act — providing containers that meet the needs of your plants while also pleasing you with their presence — is not difficult if you keep a few fundamental guidelines in mind. These include size, drainage, and material. When interior decor is your priority, it is usually best to choose the container before you choose the plant. Once the container and plant are in place, you may find that a third element, such as a small piece of statuary, works magic in bringing the composition to life.
Keep in mind that flat surfaces, such as floors, tabletops, and windowsills, are not the only places to keep plants. Various types of hardware — including hooks, chains, and fiber hangers — can be used to turn almost any container into a hanging basket, or you can use a container designed to be suspended from a hook. This is often a great way to give a plant bright light that might otherwise be wasted. When installing a hook in the ceiling or mounting hanging hardware on a wall, make sure it is firmly anchored into a joist (the solid pieces of wood behind sheetrock). Otherwise, only very light plants, such as tillandsias (air plants), will be suitable for hanging.
Size. Regardless of the material from which a container is made, its size should be proportional to that of its occupant. As a rule of thumb, measure the height of the plant from the soil line to the highest leaf. Divide this number by 3, and you have a good guess as to the ideal diameter of the container, measured in inches.
Choose containers in proper proportion to the size of the plant. A container that is about one-third as tall as the plant often works best.
This equation won’t work with low-growing, vining plants or small, squat cacti, so the next size-wise guideline is to choose the smallest container that will accommodate the roots of the plant. There are two reasons to go small with containers. One is that small containers have a dwarfing effect on plant size, which is usually desirable under indoor conditions. Second, soil that is not employed in the service of roots tends to hold onto excess moisture, which in turn sets a tempting table for fungi that cause roots to rot.
The diameter of the top of the pot (the measurement between opposite edges) is usually about the same as its depth. However, some plants with shallow surface roots do better in a low, squat container. Notice, too, that pots that narrow toward the base are prone to toppling over when planted with tall plants, though they are fine for small ones. Heavy pots with attached drainage dishes are often ideal for top-heavy plants. If a tall plant insists on tipping over, move it into a square planter that sits solidly in place.
Drainage. Whatever their size or shape, containers for plants must have drainage holes in the bottom through which excess water can escape. Several midsized drainage holes are better than one large one. Many gardeners place a piece of screen over the holes to keep soil from coming out along with excess water, but it is better to leave the holes unobstructed. That way, you can check for the presence of roots growing out of the bottom of the pot, and if drainage problems develop you can reopen the holes by poking them with a skewer, awl, or pencil. If soil loss is a big concern, simply line the bottom of the pot with a thin layer of pebbles or broken crockery when repotting your plants (see page 309). A half inch of loose pebbles or broken crockery improves drainage too.
Unfortunately, many beautiful brass, ceramic, or hand-thrown pottery planters do not include drainage holes. Holes can be drilled into plastic or fiberglass, but don’t try this with fine ceramic or pottery. Instead, use these as cachepots, the term used to describe “containers for your containers.” Place an inch of clean pebbles in the bottom of the cachepot, and set your plant in a container that can be slipped inside the drainless one. (It’s common to use a thin plastic pot for the inner one.) As long as water is not allowed to form a deep puddle that keeps plant roots too wet, this double-potting system works quite well. If you accidentally overwater, be sure to drain off any excess that pools up in the bottom of the cachepot.
If a decorative container has no drainage holes, line the bottom with a layer of pebbles, and grow your plant in a well-drained container that can be slipped inside the prettier one and set on the pebble bed.
Materials. When purchased, most plants are growing in plastic containers. Plastic is lightweight, holds moisture well, and seldom breaks as plants are packed and shipped. There certainly are attractive plastic containers, but those supplied by greenhouse growers are more practical than pretty. Once a plant has had a few weeks to adjust to conditions in its new home, a container upgrade is usually in order. Possible materials include clay, better plastic, fiberglass, and ceramic.
TERRA-COTTA CLAY POTS. It is hard to criticize the handsome good looks of a healthy houseplant situated in the favorite choice, a clean clay pot set atop pebbles in a matching tray. Earth-toned clay pairs well with plants, and in the interest of uniformity, some people grow all of their plants in clay pots. Because it dries quickly, clay is the preferred container material for plants that like periods of dryness between waterings, such as bromeliads and orchids. If you find that clay pots dry out too fast, you can paint their insides with paraffin or any color of latex paint. Or you can shop for dense Italian clay pots, which usually have “Made in Italy” stamped on the bottom. These cost more than comparatively porous Mexican-made pots and are usually a shade darker in color.
PLASTIC POTS. Always supplying superior moisture retention, plastic pots come in a variety of colors and finishes. Those with a dull matte finish often must be tapped with a finger to see if they are ceramic or plastic! Many plastic pots also have snap-on trays, which do a great job of capturing water that drips from the bottoms of the pots (an especially desirable feature for hanging baskets). If you want a container in an unusual shape, such as an oblong box or a certain size of pedestal, you are most likely to find it in plastic.
GLAZED CERAMIC CONTAINERS OR FIBERGLASS CONTAINERS. Designed to look like fine clay or ceramic, these are usually the pots of choice for formal living rooms. Good-quality fiberglass containers can be costly, but with a little care they will last a lifetime. Some contain enough metal to create a burnished finish, and fiberglass containers can be painted or antiqued if you want to make them fit a certain color scheme. Fiberglass containers are also quite lightweight, which makes them a top choice for large houseplants. Better garden shops carry fiberglass pots in a range of sizes and colors, including many that are replicas of classic Mediterranean styles. Select these with the same care you might put into choosing a piece of furniture.
Smaller plants are most appropriate for ceramic containers, particularly pots that include an attached or matching drainage tray. When protected from abuse, ceramic containers often outlive the plants they are partnered with, so keep versatility in mind when investing in ceramic pots. Neutral grays and browns are easy to work with, and do not compete with plants for attention.
Regard plant containers as a long-term investment. Choose containers that work well with your interior décor, suit your personal taste, and include drainage holes through which excess water can escape.
THE MORE STRIKING THE FOLIAGE, the plainer the container should be. A glossy dark-leafed peace lily (Spathiphyllum) would look great in a gilt-trimmed Oriental pot, but a prayer plant (Maranta), with its dramatic, vividly marked and veined leaves, calls for a simple, single-colored container.
• Grow bulbs and other short-lived bloomers in plain plastic pots until they form buds. Then, to bring out their best, slip them into a decorative wicker basket and hide the interior container from view with moss.
• When a clay or ceramic pot breaks, pick up the larger pieces and then use a hammer to smash it into smaller pieces that can then be used to line the bottoms of containers. (You should always wear protective eyewear to avoid injury from flying pieces.)
• Clean your plant containers between uses. Scrub pots with plenty of hot, soapy water and let them soak, if needed, to remove salt deposits around the rims.
Grouping matching containers together is a good way to display plants with different forms, textures, and foliage colors.
See also Fertilizer, Insect Pests, Pruning
Unlike plants that live in the wild world of the outdoors, houseplants enjoy a comparatively clean environment, so they tend to have few problems with disease. However, their confinement in pots, with no way to escape stressful conditions, puts them at high risk for several common disorders. These disorders often look like diseases, and you are wise to consider both possibilities when working with a distressed houseplant.
Disease. Most houseplant diseases — including leaf spots and diseases that cause stems and roots to rot — are caused by fungi. Fungi somewhat resemble plants in their life cycle. Microscopic spores germinate and use enzymes to penetrate plant cells. Using the cells as food, the fungus spreads until it becomes mature, at which time it releases thousands of new spores.
LEAF SPOTS CAUSED BY FUNGI may have a sunken middle or a dark place in the center of the spot — the “fruiting” site that produces the next generation of spores. Removing leaves that show suspicious spots interrupts the life cycle by removing multitudes of potential spores. When a leaf-spotting disease is afoot, it also helps to keep leaf surfaces dry, because most of these fungi need damp leaf surfaces in order for spores to germinate and grow.
FUNGI THAT CAUSE ROOTS AND STEMS TO ROT are more secretive, and by the time the plant wilts or becomes brown and mushy near the base it is very close to death. Overwatering often contributes to this problem, especially when combined with cool temperatures. Root rot also can become established when roots are damaged during repotting, because some root rot fungi can enter a host plant only through open wounds. Contaminated potting soil or dirty containers set the stage for disaster when roots are pruned during routine repotting.
Whatever the cause, it is often futile to try to revive a plant that has suffered from rotting of its roots or basal stems. If a plant is shriveled or collapsed and you suspect root rot, remove it from its container and inspect the roots. Rotted roots are black or nearly disintegrated. Some soil-borne diseases destroy the fine root hairs and root sheaths, leaving only fragile, stripped fibers behind. Other fungal diseases leave roots intact until they have destroyed the plant by girdling stems near the soil line. Dark brown spots near the base of wilted stems are usually caused by fungal diseases. Some fungi coat the base of affected stems with fuzzy gray mycelium.
Roots that are noticeably darker than others often have been damaged by fungi. Clip them off when repotting your plants.
Plants plagued with rotting roots can sometimes be saved by propagating a healthy stem cutting, or you can simply discard the affected plant. Before using the container to grow a new plant, scrub it well with hot, soapy water, then dip it in a solution of ½ cup/118 ml chlorine bleach per gallon of water and let it dry in the sun.
Disorders. Much more frequently than they are weakened by disease, houseplants show symptoms of physiological disorders. One of the most common is brown leaf tips (described below); most other disorders are easier to prevent.
When you suspect that a plant is plagued by a disorder, go back to the basics. Make sure the plant is being given a fair chance in terms of light and temperature, and pay closer attention to watering and feeding. If you cannot provide suitable growing conditions for a certain plant, either discard it or give it to someone who can. Relieved of this needless aggravation, you can spend your energy nurturing plants that are more easily satisfied by the sites you have to offer.
“WEEPING.” Occasionally pothos and other house-plants weep droplets of moisture when they are overwatered. Increasing air circulation while reducing watering solves this problem.
OEDEMA. Peperomia and some succulents actually suffer ruptured tissues when overwatering coincides with low light conditions. This condition, called oedema, causes corky bumps or ridges to form on stems and leaf undersides. Affected leaves may eventually turn yellow and fall from the plant. Keeping the plant warmer and watering less stops the damage.
When forced to take up too much water, some plants develop bumpy ruptures in their leaves or stems, a condition called oedema.
LEAF SHED. Plants shed leaves for a number of reasons, including over- or underwatering, changes in light or temperature, or as part of their normal growth pattern. Many plants shed a few leaves in the weeks immediately after they are moved, but if a plant continues to shed leaves despite good care, it should checked to see if it needs repotting. The combination of rootbound growing conditions and scant fertilizer often causes plants to turn yellow and shed their oldest leaves.
FAILURE TO THRIVE. Air pollution can cause plants to fail to thrive, and plants, like people, tend to slow down as they reach old age.
BROWN LEAF TIPS. One of the most common physiological disorders is the browning of leaf tips, which can be caused by tainted water, erratic watering, overfeeding, or a combination of factors. Plants with long, strappy leaves are most likely to develop brown leaf tips because moisture and nutrients must make such a long trip to keep cells at the leaf tips well supplied with moisture and nutrients.
In many plants, brown leaf tips is a symptom of tainted water, uneven watering, or overfeeding.
See also Interiorscaping, Propagation, Pruning
Diamonds may last forever, but houseplants seldom do. Sometimes their life spans are measured in mere weeks, while others may stay with you for decades. How do you decide when to give up on a struggling houseplant? Disposing of a houseplant often feels like a small death — the price we pay for our attachments to our green companions. Yet it is always best to allow plants to die when their time comes, and often even to hasten their death by pulling them from their pots, scattering the soil in an outdoor flowerbed, and then cleaning up the container to get it ready for a new tour of duty.
Of course, you don’t want to throw in the towel too soon. Some plants seem to be dead when they are merely dormant, so check the plant profiles in Parts 1 and 2 to see if your plant sometimes rests in a dormant state. Many plants that develop tuberous roots do rest between growth cycles, and it can be great fun to coax them back to life when they are ready.
Plants may also respond to your help should they become overgrown and woody. Pruning them rather aggressively — and propagating some of the prunings as rooted stem cuttings — can accomplish two purposes: rejuvenating the parent plant, and creating vigorous young offspring. Plant propagation does involve time and trouble, so it is most appropriate for plants you truly like and want to keep around for future seasons of enjoyment.
Be honest with yourself about this, because sometimes you may not like a plant, or perhaps you feel that it does not like you. This is a valid reason to let it go. If the plant is in good health, find it a new home (see “Adoption Options for Homeless Houseplants”). Its new owner may be delighted, and you can follow your heart to abetter plant choice for you—a win-win situation. Take what you learned from the plant about the site and care you have to offer, and use that knowledge to select a new plant that’s a perfect match to the place and its keeper.
IF BROWN LEAF TIPS DRIVE YOU NUTS, you can improve your plant’s appearance by either snipping them off with sharp scissors or growing plants with round or blunt-tipped foliage. You can also use a razor blade to taper the cut when removing brown leaf tips. Whatever instrument you use, cut just outside the line where green leaf tissue turns to brown. Cutting into the green part of the leaf can cause a new brown margin to form.
Trim off brown leaf tips.
You are under no obligation to keep a plant that refuses to thrive or is long past its prime. Plants received as gifts associated with landmark events such as marriages, births, and deaths carry an emotional charge for their keepers. Should the plant lose vitality, we may worry that the event it symbolized has become tainted or lost its meaning. This is rather silly, and it is a drama of which the plant is completely unaware. A little grieving for the plant may be in order, but then let bygones be bygones and move on. Get a healthy new plant, perhaps of a species or variety that you have admired in other places, and your sorrow will be short lived. Houseplants should be pleasures rather than burdens.
As much as we might like to live free of our tendency to judge others (and be judged as well), it happens. Unhealthy or decrepit houseplants can be the basis of negative judgments, which may be no big deal if the poor things are in your home. But in a business setting, stressed-out plants are simply unacceptable. You and your coworkers may be accustomed to sharing space with feeble, misshapen plants, but strangers may find their presence shocking or even depressing. People who know healthy houseplants find it painful to encounter distressed ones, so do yourself and the world a favor by getting rid of them. This can be a very positive move! Even if the office budget — or time constraints — do not allow for refurbishment projects, discarding feeble plants and replacing them with vigorous new ones may be the next best thing. At home or at work, a revitalized interiorscape infuses the space with vibrant new energy. Even though you may resist the idea at first, you’ll likely be amazed at the difference when shabby old plants are removed.
When you let go of old plants, consider the new opportunities that await you. If you enjoyed having a pot of dainty daffodils on your kitchen table in spring, perhaps a Persian violet (Exacum) is just the thing to take its place. But don’t rush to replace a departed plant with the first candidate you see. When a vacancy opens up in a good plant-growing space, shop around and consider a range of prospects before you settle on the next houseplant you will call your own.
See also Fertilizer, Watering
The process of flushing out the soil in a container by drenching it with water to remove excess salts is sometimes called double watering. And, in situations where a container has dried out completely, watering the plant twice will restore the moisture level in the pot. See “Flushing Out Excess Salts” and “Rehydrating Parched Plants” for more details about these watering procedures.
See also Containers, Repotting, Soil
The process through which water moves through roots and soil is called drainage. When drainage is slow, roots are often forced to sit in water, which causes them to run short of oxygen and possibly rot. When drainage is very fast, roots may not have time to take up water before it disappears. How fast or slow a container drains depends on the size and number of drainage holes present in the bottom of the container and how well they are working, as well as on the texture of the potting medium and the density of plant roots. The size and shape of the container affects drainage, too. Tall, narrow containers tend to drain quickly near the top, though the bottom section of the container may still be very moist. Low, broad containers usually drain in a more uniform fashion.
All houseplants require containers that have holes in the bottom through which excess water can escape, or drain away, yet they vary in their drainage requirements. Plants that grow best when they dry out between waterings — for example, most cacti and succulents, and some bromeliads and orchids — benefit from a planting system that provides fast drainage. Such a system is comprised of small containers with numerous drainage holes, filled with a very porous potting mix. Plants that prefer constant moisture around their roots fare better with moderate drainage, which is created by growing them in containers with fewer drainage holes and a dense, moisture-retentive potting mix.
Your choice of container size and potting mix can be tailored to meet the needs of each plant, but with all plants it is important that the drainage holes remain open. The simplest way to do this is to line the bottoms of containers with a layer of coarse pebbles, shards of broken clay flowerpots or old dinner plates, or a few small stones, set so that water can flow around them and then out through the holes below. In addition to enhancing drainage, a loose layer of rocky fill keeps the potting medium from crumbling out through the bottoms of the pots. Small containers are fine with a thin layer of drainage material (or none at all), but larger pots need more help in the drainage department. In a 6-inch container, include 1 inch of rocky fill at the bottom, increasing to 2 inches in a 12-inch pot. To limit the weight of very large containers, you may include only 1 inch of rocky fill, covered with a couple of inches of foam packing peanuts.
Gauge the depth of the layer of pebbles or broken crockery placed in the bottom of the container to the size of the pots. When using very large pots, you can increase the depth of the drainage layer without increasing weight by using foam packing peanuts atop a thin layer of pebbles.
Despite the use of rocky fill, sometimes soil or roots block the drainage holes. If you thoroughly water a plant and little or no water drains out through the bottom, there is likely a problem with blocked drainage holes. Lay the pot on its side, and open any blocked holes with a slender skewer, awl, or pencil. Check the pot again the next time you water. If drainage is still slow, or if roots are emerging from the drainage holes, make plans to repot before root rot becomes a problem.
MANY BLOOMING HOUSEPLANTS include decorative wrappings over plain plastic pots. These wrappings also cover the drainage holes, which can cause serious problems for the plant. You can have the pretty wrappings and a healthy plant, too, if you take a few minutes to make necessary renovations. Choose among the options below for fixing this looming drainage problem.
• Place a rubber band around the bottom of the pot, and use your fingers to locate the drainage holes in the bottom. Use a small pair of scissors to cut holes in the paper or plastic wrapping, or cut away the bottom section of the wrapping altogether. Set the plant in a transparent plastic tray lined with a thin layer of pebbles or color-coordinated aquarium gravel.
• Carefully remove the wrapping, setting aside the ribbon that holds it together. Cut a round from a disposable plastic plate, fit it into the bottom of the wrapping, and top it with a thin layer of pebbles, aquarium gravel, or sand. Place the plant back into the wrapping and resecure the ribbon.
• Moss-lined baskets usually include a plastic liner to keep water from seeping out onto tabletops or other furniture. This is fine for short-lived forced bulbs, but for more long-lived plants it is best to disassemble the basket, cut out the plastic liner, and dispose of it. If seepage is a problem, set the container on a plate or plant tray.
Insert a plastic plate filled with pebbles under the pot to correct the situation when purchased plants include a decorative wrapping that blocks drainage holes. When you’re done, you can re-wrap the plant if you like.
Note also that the use of rocky fill in the bottom of the pot is not mandatory if you set pots atop trays filled with damp or dry pebbles, which accomplishes the same purpose in terms of drainage and provides an easy way to increase humidity near the plants. Some plants need every bit of space within the pot for roots, and little or no rocky fill gives them the room they need, while making it easier for you to examine the plant’s root situation through the drainage holes.
See also Repotting, Soil, Watering
The primary energy force for plants is light, but they also need nutrients that support strong growth. Here are some fertilizer guidelines:
• As a general rule, fertilize plants whenever they are actively producing new growth, which for most plants is spring to fall, when light levels are high. Plants kept under lights should also be fed in winter, but feeding plants that are resting in weak winter light can do more harm than good.
• Feed plants when the soil is moist. Plants that have been stressed by dry soil conditions may take up more nutrients than they can use when fertilized before they have a chance to rehydrate roots, leaves, and stems.
• Withhold fertilizer from newly purchased plants or plants that have been moved to a new place, because the task of adjusting to new conditions is difficult enough without the additional pressure to produce new growth.
• As a broad general rule, wait at least 6 weeks after repotting plants in fertilizer-enriched soil before you begin feeding them again. Plants usually need no fertilizer for several weeks after they are repotted into potting soil that includes fertilizer. Most potting soils do include a bit of starter fertilizer, and it is best to allow plants time to make use of these nutrients before giving them additional food. Knowing when to begin feeding freshly repotted plants is part of the grower’s art, because several factors influence the rate at which the plants use the fertilizer, including light, temperature, frequency of watering, size of the root mass, and overall growth rate of the plant.
Choosing plant fertilizers. Feeding your plants need not be complicated. A few plants respond best to special fertilizers, but most houseplants are easily fed with a balanced house-plant food, a high-phosphorous houseplant food, or a high-nitrogen foliage plant food.
The differences between these three types of fertilizer is based on the fertilizer analysis, which is represented by the three hyphenated numbers on the fertilizer label. These numbers stand for nitrogen, phosphorous, and potassium. Here is what each nutrient does:
NITROGEN, the first number, supports the production of new stems and leaves. Young plants and foliage plants benefit from plenty of nitrogen, which is especially important for foliage plants that are growing rapidly, as many do in spring and early summer. In addition to a high first number in the fertilizer analysis, high-nitrogen houseplant foods usually say something about “foliage” plants on the label.
PHOSPHOROUS, the second number, is essential for all plants, but particularly important for flowering houseplants. Plants are encouraged to produce buds and blossoms by plant food rich in phosphorous. Many (but not all) African violet foods are high in phosphorous. When looking for a high-phosphorous food for blooming houseplants, look for an African violet food in which the middle number (phosphorous) is approximately twice as big as the first one (nitrogen): for example 1-3-2 or 8-14-9. Fertilizers with extremely high middle numbers are often called “bloom start” fertilizers. These are more appropriate for using outdoors for feeding plants that are growing in open soil than for feeding houseplants. Because their roots are restricted to pots, even house-plants that grow best with a high-phosphorous fertilizer need a bit of balance in their diet.
POTASSIUM, the third number, improves the functioning of roots and supports plants’ ability to move moisture and nutrients to all of their tissues.
In balanced houseplant fertilizers, which are often called all-purpose plant foods, the three numbers are roughly the same, indicating a balance of the three major nutrients. The three most popular balanced houseplant foods show these nutrient analyses on their labels: 8-7-6, 6-5-6, and 20-30-20; other balanced fertilizers show analyses of 7-7-7, 20-20-20, and so forth. As long as the numbers in the analysis are close, the product qualifies as a balanced fertilizer. Most of your houseplants will grow best using this type of fertilizer.
Understanding micronutrients. As well as nitrogen, phosphorous, and potassium, plants need small amounts of other nutrients, often called micronutrients. Micronutrients such as calcium, copper, iron, and magnesium are present in fresh, good-quality potting soils, but plants that are repotted infrequently benefit from plant foods that replenish their micronutrient supply. When buying houseplant fertilizer, try to choose a product that includes at least a short list of micronutrients.
Don’t discard a plant food because you see no micronutrients listed in the fine print, however. Magnesium can be provided by adding a pinch of Epsom salts to water, or you can mix up a micronutrient buffet by making compost tea. Buy a small amount of bagged compost at any garden center, swirl a gallon of it with 2 gallons/7.5 liters of water, let it settle for an hour or so, and then pour off the brown “tea” and use it to water your plants.
Alternatively, you can filter the tea through a strainer lined with a paper towel, pour it into a pump spray bottle, and spray it onto plant leaves. Treating plants to compost tea twice a year, in spring and late summer, ensures that plants get all the micronutrients they need, along with naturally occurring enzymes, which often have an invigorating tonic effect on plants.
Making compost tea can be messy, but there is an alternative. Look for micronutrient fertilizers that are mixed with water and sprayed onto plant leaves. These are sold at most garden centers (or by mail order). Many of these products are made from dried, powdered seaweed, or kelp. A few are rich sources of iron, which is often needed by azaleas, gardenias, and other plants that grow in acidic soil. If you grow a variety of houseplants, consider adding one of these products to your fertilizer collection.
A word on fertilizer form. So far we’ve been discussing the chemical side of fertilizer, but you also have a choice of fertilizer forms — liquid concentrates, powders, crystals, tablets that dissolve in water, spikes that are pushed into the potting soil, or time-release fertilizers, which are coated granules that slowly release nutrients as they dissolve.
For most plants, the best choice is a liquid or mix-with-water powder or crystal form, which gives you tight control over how much fertilizer goes into the pot. One is no better than another, though liquids dissolve very quickly, and do not clump or melt when exposed to high humidity as powders and crystals sometimes do. Both liquids and soluble powdered fertilizers are available as organic products, derived from natural materials, or you can use synthetic forms (plants don’t seem to be able to tell the difference). Spikes are quite unpredictable, and should be used only when you anticipate a long absence when you must leave your plants in the hands of an inexperienced plant-sitter.
Very large, long-lived houseplants such as palms, Norfolk pines, and others that grow into small trees can easily be fed by scratching 1–2 tsp/5–10 ml of coated time-release fertilizer into the top .5 in/1.25 cm of soil. You can also use a balanced organic fertilizer, which releases nutrients slowly as it decomposes. With either organic or time-release fertilizer, a small amount of fertilizer dissolves and moves down into the soil each time the plant is watered. Commercial growers use these products extensively, and you will often see a few round yellowish or greenish pellets on the soil’s surface of newly purchased plants. It is fine to leave these alone until you repot the plant. When you replace the soil, simply discard them along with the old potting soil in any convenient outdoor bed.
• SIGNS OF TOO LITTLE FERTILIZER. Weak new growth, in which new leaves are small and pale, is a classic sign of too little fertilizer. Plants suffering from micronutrient deficiencies often show unusual yellowing of tissues between leaf veins, or pale leaves with darker leaf veins. When starved plants are given one or two feedings with an appropriate plant food, their leaf color usually improves quickly, becoming greener in a matter of days.
• SIGNS OF TOO MUCH FERTILIZER. Very dark, lush leaves with some browning or curling of leaf edges suggests too much fertilizer. Blooming houseplants may refuse to produce buds when given too much nitrogen.
Very dark-colored leaves with slightly curled edges are often signs that the plant is receiving too much fertilizer.
Very light-colored leaves often indicate that a plant is underfed, or that it is being stressed by too much light.
Troubleshooting fertilizer problems. Plants give you clear signs when they are receiving just the right amount of plant food. For instance, when older leaves have good color, and new leaves steadily appear, gradually attaining a size that compares with that of the older leaves, you’ve got the fertilizer routine just about right. The common indicators listed above, as well as many other nutritional disorders, are described in the troubleshooting sections of commonly affected plants in Parts 1 and 2. Before deciding that a plant is over- or underfed, evaluate other variables such as light, temperature, and proper watering practices. The closer each of these conditions comes to a plant’s ideal, the better its prospects for living a long, productive life.
See also Watering Diseases and Disorders, Insect Pests
Most of the diseases that give rise to leaf spots on otherwise healthy leaves are caused by various fungi, and fungi also cause diseases that result in root rot. These problems are discussed in detail on page 255. However, plants that show dark, dirty-looking deposits on their leaves are probably not suffering from a fungal disease. Blackish “dirt” is usually sooty mold, which grows on the honeydew excreted by sucking insects. You can rule out fungus as the problem if you can wash off the deposits with lukewarm, soapy water. As you clean away the sooty mold, look for its cause, which is likely to be scale, mealybugs, or another insect that sucks plant sap. See page 268 for more information on these pests.
To keep your houseplants looking their best, take time every 2 to 3 weeks to relieve them of old leaves, while taking stock of their general condition. You might think of these grooming sessions as wellness patrols — the time when you practice good preventive health care while improving the appearance of your plants. You can use your fingertips to pinch off failing leaves from many plants, but a small pair of scissors makes a cleaner cut and avoids any twisting of stems.
Health patrol. As you remove withered or yellowed leaves, check your plants carefully for evidence of insect pests or diseases. Insect pests often hide on leaf undersides, while leaf spots with circular or halo-type patterns are often caused by fungal disease. When entire branches show signs of pest problems, go ahead and snip them off. Pest-damaged foliage never recovers its vigor, and it does no good when left on the plant. Pick up withered leaves that lie crumpled on the soil’s surface as well, because they can harbor diseases and insect pests, too.
Never pull on plants when removing withered foliage. Use small pruning shears or sharp scissors instead.
Precautions. Most leaves that are shed by plants are not troubled by pests. Shedding leaves is more often the plant’s way of letting go of the old and making way for the new. As you aid in this process, the plant benefits from improved air circulation and light exposure, and of course the plant looks better, too. Plants that have shed most of their lower leaves and become unattractive in the process can be staked, prepared for propagation, or possibly discarded.
Before your green companions’ ancestors became houseplants, every one of them enjoyed life outdoors, many in extremely humid jungle environments. On their way to your home, the progeny spent weeks, months, or years in humid greenhouses. Compared to these settings, modern homes and offices are quite arid, especially in winter when heated air becomes extremely dry. When you take a plant that’s accustomed to a very humid environment and force it to grow in dry air, it may not be able to adequately replenish moisture lost through its leaves. Leaf tips and edges may become dry and turn brown, or the plant may shed many of its leaves. Plants with thin leaves or those with long, strap-shaped foliage tend to suffer most from low levels of humidity.
You always have a choice between altering indoor humidity to meet the needs of plants or changing your plant choices in keeping with prevailing humidity. Several ways of raising indoor humidity are described below, or you can stick with plants that adapt to low humidity, such as cacti and succulents. Another option is to grow plants that need high humidity in a terrarium — a perfect solution to providing a humid place for plants in dry offices, or for enjoying the company of plants if you suffer from numerous allergies. See page 323 for details on planting and caring for a terrarium.
In winter, when indoor air is quite dry, group high-humidity-loving plants together on a pebble-lined tray that can be filled halfway with water. To further raise humidity, place glasses or bowls of water among the plants.
Humidity means the amount of water vapor present in the air, and it is measured with an instrument called a hygrometer. But you do not need a hygrometer to know some basic things about prevailing humidity. Rooms in which water is often used, such as the bathroom and kitchen, tend to be more humid than other areas of the house. If you keep plants that crave high humidity, try to place them near sources of running water.
Plants are constantly taking up moisture through their roots and releasing it through their leaves, so to some extent, they create their own humidity. In a study done at Washington State University, simply adding several plants to a computer lab increased humidity by about 10 percent while reducing the amount of dust floating in the air. However, plants that need high humidity cannot turn a very dry environment into a comfortably humid one without a little help. One very simple strategy for increasing humidity is to place plants close together, because groups of transpiring plants form pockets of humidity on their own. There is some natural symmetry here, in that we tend to fill our brightest indoor spots with closely spaced plants. Placing bowls or glasses of water between plants increases humidity while keeping water handy for dribbling into containers.
To further increase humidity, you can place plants on watertight trays filled with clean pebbles, which are then covered halfway with water. The water should not be so deep that it reaches the bottoms of the containers, which can cause roots to rot. The trays also need to be rinsed every few weeks to keep them from becoming a secret haven for fungus gnats or other pests. Regular cleaning also limits the amount of salts that accumulate on the pebbles as water evaporates.
Misting plants, by spraying them with a fine spray of water, is helpful for plants that need unusually high humidity, but for some plants it can do more harm than good. Plants with hairy leaves, such as African violets, dry very slowly, and leaves that stay damp for long periods of time can develop problems with disease. However, a few plants, such as bromeliads, actually take up moisture through specialized scales on their leaves, so misting them accomplishes two things — the plants absorb moisture, and they enjoy increased humidity.
Misting plants from time to time when the air is very dry is a sound practice, but you should not mist heavily without a specific purpose in mind. Do mist plants that are at high risk of developing problems with spider mites, which often follow on the heels of very dry conditions. Keep in mind that misting is not a substitute for a thorough rinse, which is the best preventive measure for this pest. Misting is also helpful in early winter, when humidity levels fall in keeping with an increase in indoor heating, or as a way to ease the adjustment of new plants that are accustomed to greenhouse conditions. Once plants have 2 to 3 weeks to adjust to such changes, it is best to allow humidity to gradually drop to levels that are comfortable for both you and your plants as opposed to continuous heavy misting. Most people and plants are comfortable in rooms where the humidity level ranges between 40 and 50 percent. Running a humidifier in rooms where a number of plants are kept is usually the best solution in buildings with extremely dry indoor air.
See also Cleaning, Diseases and Disorders, Grooming, Moving Houseplants, Propagation.
Like other plants, houseplants are occasionally bothered by insects. When houseplants are moved outdoors in the summer, a number of insects, including various caterpillars, earwigs, and other critters that are seldom seen indoors, may breakfast on plant leaves or buds. Taking appropriate precautionary steps when bringing plants in following their outdoor summer vacation, as outlined on page 291, will greatly reduce the likelihood that you will see insects on your houseplants.
Yet a few insects, including the eight described in detail here, have no trouble colonizing plants that never move from the places you select for them. In alphabetical order, these include aphids, earwigs, fungus gnats, mealybugs, scale, spider mites, thrips, and whiteflies. On page 278 you will find five insecticides that can be safely used to treat insect problems on houseplants.
The most common way for any of these insects to gain entry to your home or office is by hitching a ride on new plants, where they may be hidden in crevices, or there may be one or two microscopic eggs attached to the underside of a leaf. For this reason, many people keep new plants separated from others for 3 to 4 weeks, during which time any lurking insect problems have ample time to become apparent. Isolating plants does not mean that you need to keep them in a separate room. A distance of 10 ft/3 m or so is sufficient to keep minor insect populations from moving from one plant to another, because insects seldom seek new host plants when they are satisfied with the one they have.
The diversity of species among houseplants also gives you a degree of protection from insect epidemics. The insects described here can infest a number of different plants, but insects vary in their ability to digest the juices of specific plants. For example, if you have a dish garden in which the English ivy becomes infested with spider mites, you may find that dieffenbachia grown only a few inches away remains unaffected. So, when you must take steps to control insects that turn up on a certain species, it is seldom necessary to subject all of your plants to washing or spraying. Do, however, watch neighboring plants closely. If a new outbreak is going to occur on a previously unaffected plant, it will usually do so within a month.
In addition to looking for insects, look for what they leave behind, which is tactfully referred to as honeydew. Most insects that infect house-plants suck plant juices, and their excrement is usually this sticky liquid. Leaves that show shiny patches or the presence of a sticky residue on surfaces near plants are evidence of feeding by sucking insects including aphids, mealybugs, scale, and some other species. If the insects have been present on the plant for some time, the honeydew darkens to what is called sooty mold. Both honeydew and sooty mold can be cleaned off with warm, soapy water and a soft cloth, but controlling the insects that created the mess often requires more extensive efforts.
Plants that have had more than half of their leaves damaged by insects are often not worth saving. However, if the plant can be propagated from a stem cutting and you find a stem that appears insect free, you can try rooting the cutting as described on page 299. This is often the best way to retain a beloved plant that has been ravaged by insects.
Description. Where there is one aphid, there are many more, because these tiny sucking insects always appear in groups. They can hitch rides indoors on plants, people, or pets, and because female aphids are born pregnant, they quickly form colonies when they find a suitable host plant. Many plants can host aphids, which are most commonly found on tender young leaf tips, the undersides of new leaves, or the buds of blooming houseplants. Because aphids suck plant juices, infested stems and leaves often are curled or distorted.
Most aphids are less than 
in /.3 cm long, round or oval in shape, with colors that range from green to yellow to red. Some aphids develop wings, while others do not. When many aphids feed on a plant, they leave behind a sticky residue that makes leaves shiny and often causes gummy specks to form on tabletops and floors beneath infested plants.
Aphids are usually found in dense colonies, feeding on tender new growth at stem tips. Pinch off heavily infested stems before trying other control measures.
Control. Fortunately, aphids are not difficult to control. The first thing to do is clip off stem tips that are heavily infested. If only a few aphids are present, you can remove them with a cotton swab dipped in alcohol. For more serious infestations on large plants, clean the plants thoroughly in a lukewarm shower or take them outdoors and spray them with a fine spray from the hose. The spray will dislodge many aphids, though some will survive hidden away in leaf crevices. You can get these stowaways by repeating the procedure after a few days. Very small plants can be cleaned by dipping them in a sink of soapy water after first enclosing the container and soil in a tightly wrapped plastic bag. (See “The Dope on Soap” on page 271.) Insecticidal soap kills aphids quickly and easily, so it is a good idea to make a practice of spraying all plants kept outdoors in summer with a dilute soap spray before you bring them indoors in the fall.
Description. The pincers found on these prehistoric-looking insects look scary, but they are much too weak to penetrate human skin. There is also no truth to the old superstition that earwigs crawl into sleeping people’s ears and eat their brains. It is a fact that earwigs are attracted to the cool dampness on the undersides of flower pots. They are most often seen on plants shifted outdoors in summer, but sometimes earwigs sneak indoors and find safe havens beneath houseplant containers. Earwigs rarely cause serious damage to plants, though they will eat roots and leaves rather than starve to death.
A cigar-sized roll of damp newspaper placed next to plants is an easy way to capture earwigs, which are most active at night.
Control. Indoor conditions are usually too dry for earwigs, so they do not reproduce indoors. You can gather them with a vacuum cleaner if you don’t want to touch them, or you can trap them. Roll a piece of newspaper into a hollow, cigarsized roll held tight with rubber bands, dampen it well, and place it where earwigs have been seen. At night, the earwigs will crawl inside the tube, and you can dispose of it first thing in the morning. Earwigs are also easy to trap in small sticky traps, such as those used to capture ants, roaches, spiders, and other small insects. Sticky traps are widely available at supermarkets and discount stores. Be sure to place them out of the reach of children and small pets.
Description. When you notice slender, dark gray 
–⅛ in/.2–.4 cm long flies flitting about atop the soil in a houseplant, or when tiny flies congregate in warm windows or near your favorite reading light, you know you have a problem with fungus gnats. Often fungus gnats sneak indoors through open doors or windows and then breed in the damp soil of houseplant containers. Adults may lay 300 eggs at a time, which hatch a week later into tiny, threadlike larvae. The larvae feed on rotting vegetation in the soil as well as on tiny plant roots. After feeding for 2 weeks, they pupate into adults. Plants growing in severely infested soil appear weak, grow poorly, and often shed older leaves.
Control. The first thing to try is to allow the soil to dry out between waterings, because fungus gnats need constant moisture. If problems persist, try trapping the adults and larvae. Adults are attracted to yellow sticky traps placed near lights. Attach a piece of yellow plastic or poster board to a wooden skewer or stick, coat it with petroleum jelly, and install it in an infested houseplant placed near a lamp, like a gnat-catching flag. An old remedy for trapping the larvae involves pushing slices of raw potato into the soil, which attract the larvae. Gather the potato pieces and dispose of them every 2 days. As a last resort, repot the plant in fresh soil.
Fungus gnats that defy these control measures can be quickly eradicated by drenching the soil with a special strain of Bacillus thuringiensis (Bt israelensis), which is sold as Gnatrol. This product is widely used in commercial greenhouses, and it is safe and effective.
Make sticky traps for fungus gnats by coating a small piece of yellow plastic or poster board with petroleum jelly.
Description. Numerous houseplants are subject to attack by these strange sucking insects, which are often brought into homes and offices on infested plants. Mealybugs are experts at hiding in small nooks where leaves join stems, and some species feed on plant roots. Adult mealybugs are ⅛–⅜ in/.2–.9 cm across, and look like whitish cottony blobs, which loosely attach themselves to stems, leaves, or roots. They weaken plants by sucking plant juices. The white coating on the adults, nymphs, and eggs protects them from sprays with water or pesticides, so the best way to control them is by hand.
Mealybugs are easily removed by hand. Use a cotton swab dipped in rubbing alcohol, which usually kills the uncollected mealybugs. Or, pick them from plant stems and leaves with tweezers.
Control. Begin by using a fingernail, toothpick, or cotton swab dipped in rubbing alcohol or vegetable oil to dislodge and collect all the mealybugs you can find. Pay close attention to the places where leaves are attached to stems, which is a favorite place for mealybugs to hide. Repeat this procedure weekly until the plant is free of mealy-bugs. If the plant tolerates insecticidal soap, a thorough spray will often kill any mealybugs you missed.
African violets, cacti, and some other house-plants are attacked by mealybugs that feed on plant roots. Sometimes you can find root-feeding mealybugs on the bottom of the pots, or you can allow the roots to dry a bit and then tap the plant out to inspect its roots. If mealybugs are present, gently repot the plant in clean soil and then take it outdoors and drench the roots (but not the leaves) with an insecticide such as carbaryl.
When any type of mealybug problem develops in greenhouses, a natural predator called the mealybug destroyer is often released, and it does a good job of hunting down and killing mealybugs. However, using this small black lady beetle is not practical in homes and offices unless a large collection of plants is seriously infested with the pest.
Description. Scales are bizarre little insects that attach themselves to plants and suck plant juices. Most species are exclusively female. When males do occur, they do not have mouths, and therefore live but for a short time. Once a juvenile scale attaches itself to a leaf or stem with its needlelike mouthparts, it seldom moves. Instead, it grows larger, exudes a waxy coating that forms a helmetlike shell, and bears hundreds of young, all in one place.
Several species of scale infest houseplants, including a few that normally live on outdoor trees and shrubs in mild climates. Others are tropical species that inhabit greenhouses where houseplants are grown commercially. Wherever they come from, scales are formidable houseplant pests. They can infest hundreds of different types of plants, but tend to be most troublesome on ficus and ferns.
The evidence of scale infestation is easy to detect. Affected leaves or stems may be weak and slightly yellow, and there is often a sticky substance on the table or floor beneath the plants. This is honeydew excreted by the scale as they feed on plant juices. Most scale are found on stems or leaf undersides, especially near the central leaf vein. They may be brown, gray, or black bumps, which are often shaped like flattened discs. Fully grown adults range from –⅛ in/.2–.4 cm in diameter. Juvenile scales, called crawlers, do move about, but they are so small that they are very difficult to see.
Use a soft cloth dipped in warm, soapy water to remove scale from leaves and stems.
Control. Practice prevention of this pest by thoroughly cleaning any ferns or ficus that spend the summer outdoors before moving them back indoors for the winter. Treating plants with insecticidal soap a week or two before they are brought indoors is an excellent preventive practice. Some ferns are damaged by soap, so test a sample frond before treating the entire plant.
Should you discover scale on any houseplant, your first line of defense is to attempt to clean it by hand using a soft cloth dipped in warm, soapy water. Although this is laborious, it is worthwhile if the infestation is light and you value the plant. On cactus and other untouchable plants, use a cotton swab dipped in soapy water or oil to remove scale.
After removing as many scales as you can, treat the plants with insecticidal soap, and then place them in a shady place to rest. Another option is to use horticultural oil, which smothers scale insects. Whether you use soap or oil, repeat the application 10 days later to kill scales that may have escaped the first treatment. If you tried to clean away scale by hand and were unsuccessful, you will probably have better luck after you have given the plants a thorough spray with insecticidal soap. You’ll find that dead scale are easier to remove than live ones.
Several chemical insecticides can be used on scale that persists despite treatment with insecticidal soap or oil and hand cleaning, but be sure to check a sample leaf first to make sure that the plant can tolerate the chemical. Soap sprays cannot be used on palms, so when a large palm becomes infested with scale, a systemic insecticide containing imidacloprid is often the best solution (see “What about Systemics?” on page 272).
Description. Perhaps the most dreaded pests of houseplants, spider mites are not true insects, but are more closely related to spiders and ticks. Spider mites damage plants by piercing the leaves with needle-sharp mouthparts and then sucking out plant juices. They congregate on the undersides of plant leaves, where they may not be seen until the plant is seriously infested. Mite-laden leaves may show numerous yellow pinpricks, or they may be dry and limp while still green. Left uncontrolled, spider mites can kill their first victim and then spread to other nearby plants.
Spider mites cannot hurt people or pets, however, because they are so very tiny. Most adults are only 
in/.05 cm long, so you would need a 15× magnifying glass to see them. Under magnification, spider mites may be green, yellow, red, black, or colorless. Without a magnifying glass, you can usually see faint silky webbing on the undersides of badly infested leaves. Also, if you tap or brush the underside of an infested leaf over a white piece of paper, you may be able to see miniscule moving dots.
Control. Spider mites usually gain entry to homes and offices on new plants, so it’s always a good idea to keep new plants isolated from others for a couple of weeks. In dish gardens, sometimes one plant will have spider mites, but the others will be okay. This is usually because the infested plant was stressed in some way, which left it easy prey for the mites. Weak plants have more problems with spider mites than healthy ones.
Early detection is a challenge, but light infestations of spider mites are much easier to treat than severe ones. Spider mites multiply rapidly, with eggs hatching only 3 days after they are laid. A complete life cycle, from egg to egg-laying adult, can pass in only 2 weeks. Very dry conditions encourage spider mites, so they are often seen in winter, when plants struggle in dry, heated rooms. Misting plants regularly or setting them on beds of pebbles that are kept damp helps to prevent problems with spider mites.
Early control is crucial with spider mites, which can infest a broad range of houseplants. By the time you see faint webbing on leaf undersides, the mite population is dangerously high.
How you control spider mites depends on the size and value of the affected plant, and how much you want to keep it. Small, inexpensive plants that have come into your life casually are best disposed of, because in the time it takes to bring the mites under control they could spread to more significant houseplants. However, if only some parts of the plant are infested, promptly clip them off and dispose of them in a sealed plastic bag. Then treat the remainder of the plant with insecticidal soap or the soap-oil spray described on page 275. Repeat at least twice at 5-day intervals to make sure you kill new mites that hatch from eggs hidden in leaf crevices or beneath bits of webbing.
THE DAMAGE TO PLANT LEAVES caused by thrips and spider mites often looks similar, but only spider mites create a webby habitat on leaf undersides. Tap an infested leaf over a piece of white paper to correctly identify these pests. Thrips are dark slivers, while spider mites are tiny moving dots. If spider mites are present, use insecticidal soap only, and do not use chemical pesticides, which can make the problem worse. See page 274 for the best ways to handle spider mites.
To confirm the presence of thrips, shake the suspicious leaf or blossom over a piece of white paper, and look for tiny, moving, shard-shaped creatures.
Do not attempt to control spider mites with pesticides. They often do not work, and mites rapidly become resistant to them. If you have a very large collection of houseplants that are affected by spider mites, you might consider releasing beneficial mite predators to bring spider mites under control. This solution is often used in greenhouses, and it is very effective. See Resources for companies that sell beneficial mites.
Description. These tiny, sucking insects are not extremely common on houseplants, but occasionally they manage to proliferate into bothersome populations. Generalized feeders commonly seen on garden flowers, thrips can come indoors on plants, people, and pets. Once confined to your house, they have no choice but to feed on the only food available to them, your houseplants.
Thrips are quite tiny, seldom growing to more than in/.16 cm long. Adults look like dark-colored shards or bits of thread, while young thrips are usually yellowish brown. Thrips feed on both leaves and flowers. Leaves that are infested with thrips often show silvery streaks where the thrips rasp into leaf tissue before inserting their strawlike mouthparts to suck plant juices. When an infestation is severe, the leaf may pucker or curl around the thrips, and you often can see sprinklings of black feces, which look like finely ground black pepper. When thrips feed on flowers, the petals show dark spots or blotches.
To positively identify thrips, shake the plant over a piece of white paper and look for tiny moving slivers. With a very strong magnifying glass (16x or better), you may be able to see feathery wings on the largest thrips.
Control. The easiest way to control thrips is to wash them off plants with a fine spray of water. This is best done outdoors or in the shower, and it’s a good idea to rinse the plant again after a few days. Should the problem persist, spray the plant with insecticidal soap (see page 278). Several widely available pesticides kill thrips, including carbaryl. Sticky traps are also a good option. You can make your own sticky trap by coating a piece of blue cardboard or plastic with petroleum jelly or motor oil and installing it in an infested plant like a little flag. While many other pests are attracted to yellow sticky traps, thrips are drawn to bright blue.
Description. When you are faced with an infestation of whiteflies, you usually know it, because little gnatlike creatures swarm into the air when you water your plants. These are adult whiteflies, which usually grow to about in/.16 cm long and have four powdery wings. If you then use a magnifying glass to inspect leaf undersides, you may find barely visible eggs, crawlers (larvae), and pupae, all of which are very tiny and yellowish in color. Infested leaves are often pale and drooping from having their juices removed by feeding whiteflies.
Whiteflies that infest houseplants can feed on more than 60 species of plants. They may find your plants while the latter are outdoors in the summer, or you may accidentally bring them in when you adopt a new plant. Early intervention is important, because whiteflies reproduce and spread quickly. A complete life cycle can pass in only 40 days.
Control. Begin treatment by removing badly infested leaves, which probably will not recover from the feeding done by these sucking insects anyway. Then rinse the plant thoroughly, and follow up with a spray of insecticidal soap if the plant can tolerate soap sprays. Very delicate plants can be sprayed with a mixture of 4 parts water to 3 parts rubbing alcohol. Repeat this treatment every 7 to 10 days to make sure that no whiteflies survive.
Whiteflies feed by sucking plant juices, so infested leaves often appear pale or limp.
Once you have had whiteflies, it’s a good idea to monitor all plants for several months by using yellow sticky traps. Whiteflies are attracted to yellow. You can buy yellow sticky traps made for use with houseplants, or you can make your own by cutting yellow margarine tubs or other yellow plastic containers into 2 in/5 cm pieces, or you can use yellow cardboard. Attach the traps to wood skewers and coat them with motor oil or petroleum jelly. Either of these substances is sticky enough to catch tiny whiteflies. If even a few are detected, inspect all plants thoroughly and immediately take steps to bring them under control.
Before using any pesticide on a houseplant, carefully read the product’s label to make sure it is appropriate for both the pest and the plant. When any houseplant is treated with a pesticide, be sure to keep the plant in a shady place, as pesticides and bright light often combine to cause injury to plant leaves. Use the following lists as general guides; obscure houseplants are often not listed on pesticide labels. If you are unsure about a plant’s tolerance of any chemical, apply it to a test leaf and wait 3 days before treating the entire plant.
What it is. Imidacloprid is the least toxic pesticide that works on contact with insects as well as systemically, by mixing with plant sap. Insects that subsequently feed on plants are poisoned as they take up small amounts of the pesticide.
Plants with delicate leaves that may be injured by this or other types of sprays can be treated by soaking the roots with this pesticide, or by repotting into soil that has been amended with imidacloprid. This insecticide is owned by the Bayer company; products containing imidacloprid are widely available under the Bayer brand name.
Precautions. Do not apply imidacloprid concentrates indoors, and do not use this pesticide on edible plants such as rosemary or calamondin orange.
What it is. Insecticidal soaps, as well as homemade soap sprays, kill insects by cutting through their protective coatings, causing them to dry up. The spray must actually coat the insects to be effective.
Precautions. Insecticidal soaps are safe to apply indoors, but they can cause leaf injury to some plants, including those listed below. Never use insecticidal soap on newly rooted cuttings, which cannot have the functioning of their sparse leaves compromised in any way.
DO NOT USE ON:
Begonia
Crown of thorns
Ferns (not all are sensitive)
Jade plant
Palms
What it is. Neem is a natural pesticide made from a tree that makes pests stop feeding, and also interferes with maturation processes. Neem also deters several fungal diseases.
Precautions. It can safely be applied indoors. Products often have neem in their name, or you can check the label for azadirachtin, the active ingredient.
PLANTS OFTEN SENSITIVE TO NEEM:
African violet
Begonia
Crown of thorns
Ferns (not all are sensitive)
Geranium
Ivy
Jade plant and other succulents
Palms
Schefflera
What it is. Carbaryl (best know as sevin) is a synthetic pesticide that kills a wide range of insects.
Precautions. Carbaryl should not be applied indoors. When applied outdoors, it has been known to damage leaves of some plants (see below).
PLANTS SENSITIVE TO CARBARYL:
Aluminum plant
Arrowhead plant
English ivy
Ferns
Peperomia
Schefflera
What it is. Orthene (acephate) is a synthetic pesticide that is toxic to most insects.
Precautions. It can be applied indoors. Still, check the label, because it can cause leaf damage to some plants (see below).
PLANTS SENSITIVE TO ORTHENE:
African violet
Chrysanthemum
Ferns
Ficus
Geranium
Nerve plant
Palms
Piggy-back plant
Poinsettia
Prayer plant
Shefflera
See also Cleaning, Containers, Grooming, Light
Using plants to make indoor rooms look and feel more inviting is called interiorscaping. Plants always provide a green link to the outdoor world, and there is no room that does not benefit from the presence of plants. The challenge is to choose sites that suit the needs of the plant and the design needs within the room. At the same time, you may want to use plants to support a particular decorating style. Cacti and succulents evoke a southwestern flavor; dainty African violets have the ornate appeal associated with plush Victorian interiors; and numerous foliage plants bring warmth to otherwise stark contemporary decors. For any style of decor, plants become comforting focal points that naturally draw attention wherever they are placed. They also soften sharp angles, making rooms feel less confining and boxlike. Homes and offices that might otherwise seem cold and sterile feel warm and inviting when interiorscaped with living plants.
There are containers in every color and style to complement any decor.
Light is always most abundant near south and west windows, with more subdued light available from the north and east.
As you organize your ideas, think about how plants will relate to the room, and to each other. Consider also the direction from which plants will be viewed, which is often the opposite from the light source that sustains them. The best interiorscapes include some flexibility, so that plants can be rotated from one place to another to change the look of the room, while giving plants opportunities to avail themselves of excellent light. If you work with flowering houseplants, set aside one of your most prominent, brightly lit locations to showcase plants at their peak of bloom.
You can analyze potential plant sites within a room by making a bubble drawing that identifies puddles of light from windows or overhead light fixtures. Furniture does not need light, so many plant lovers plan their furniture placement around the spots within the room that are most useful to plants. And some types of furniture partner well with particular plant shapes. Small plants that are attractive when viewed from above are best for tabletops, while cascading or vining plants work well when placed atop tall mantels, china closets, or file cabinets. Long sofas often appear more anchored in place when they are flanked on one side by a tall, vertical floor plant. Where floor space is limited, install wall shelves or hangers in places where good light is available for plants. Adding a shelf equipped with supplemental lights to an otherwise dim room creates an instant indoor oasis. In terms of interior design, a shelf upon which pretty plants are illuminated serves the same purpose as a fine piece of art.
Bright windows serve as a stage for displaying the varied colors and textures of houseplants, as well as their sculptural qualities.
Interiorscape basics. Just as is true in outdoor gardens, every interiorscape is unique. However, a few simple guidelines are useful for creating orderly interiorscapes in which the plants appear to belong exactly where they have been placed.
ENTRYWAY ACCENTS. One of the most potent places for a plant is just inside the door, or at the closest location to the entry where light is available. Entryway plants are natural greeters, and they help ease the transition between the outdoor and indoor worlds. Select tough plants for this job over species that are easily injured when they are touched.
COMPANIONABLE GROUPINGS. Collections of differing types of houseplants often look best when they are arranged in groups of three or five plants, with the tallest plant placed behind or to the side of the smaller ones. This is an excellent way to capitalize on differences in plant color and texture among various houseplants.
LITTLE LANDSCAPES. In spaces where a single plant tends to get lost, try multiples instead. For example, you might locate two or three matching pots of the same plant together in the same place, which makes a strong textural statement. Or conjure up the feel of a forest by filling an indoor windowbox with different plants of similar size (they can be kept in individual containers slipped inside the planter). Dish gardens, in which several small plants are grown together in a low, broad container, can be moved from the windowsill to the dining table when you need a fast centerpiece.
Cascading plants, such as English ivy, pathos, or heartleaf philodendron, can be allowed to drape themselves over the edges of tables, mantels, tall cupboards, or file cabinets.
REPETITION. One plant is better than none, but most rooms appear better furnished when three or more plants are located where they can “balance” one another in terms of visual punch. When a diverse collection of plants is used, it is helpful to standardize containers to one type — an easy way to provide constancy of color and texture.
FRAMES. You can use plants to frame a view from a window or to draw attention to a comfortable chair or other piece of furniture inside a room. In your office, you might even frame yourself by placing an attractive plant behind you, so that people enjoy a little green scene from the other side of your desk. Plants speak softly, but they always say, “Look here.”
FOCAL POINTS. Spotlight blooming plants or specimens with variegated leaves by placing them where they can be seen up close, the same way you might do with a vase of fresh-cut flowers. But don’t overdo it: Use plain containers, and limit the number of showy plants within a scene so colors and intricate leaf patterns don’t compete with one another.
ORNAMENTS. Tabletop plants often appear more refined in the company of small statuary, paperweights, candles, or a bowl of fresh fruit. To add more color and texture, you can use a decorative placemat to make the setting complete. In narrow passageways, mirrors work magic maximizing the presence of plants.
Clockwise from top: Triangles always work well as a general guideline for positioning plants. Dish gardens often benefit from small ornamental touches that help to refine the garden’s theme. Blooming plants create a miniature garden when displayed together.
EXPANDING HORIZONS. You can get more interiorscaping ideas by visiting places where plants are artfully used. This happens automatically when you become interested in houseplants, because you suddenly notice plants that were there all along in malls, airports, hotel lobbies, plant and floral shops, cafés, and other people’s homes and offices. When you find yourself marveling at the genius of the human who came up with a lovely interiorscape, consider this alternative interpretation: We may think we are in charge of plants, since we decide where and how they will be grown, but they also control us, nudging us to do their bidding by prospering in hospitable places and cleverly using their beauty and health-enhancing talents to win our favor. In the most wonderful interiorscapes, plants have been given everything they need by caring human hands. In return, they give us clean air, invigorating views, and happy hearts. It is, in all the important ways, a very fair deal.
See also Acclimatization, Moving Houseplants
Light is the most important variable in growing happy, healthy houseplants. Because we humans run on food, we tend to think that plants depend on fertilizer (as “food”) in a very fundamental way. Certainly they do, but plants derive most of their energy from light. When deprived of light, the availability of nutrients and moisture is meaningless.
Plants make use of light through the process known as photosynthesis. Special cells within the leaves, called chloroplasts, take in light and transform it into energy. It is a small stretch to regard all plants as solar collectors. They receive, process, and store up light in the form of leaves, stems, roots, and sometimes flowers.
Plants that prefer high light contain numerous chloroplasts, which assemble into thick layers within the leaf tissues. The chloroplast layers within the leaves of low-light plants are comparatively thin. Yet plants can adapt to changing light levels by altering the density and arrangement of their chloroplasts. This happens naturally as light levels change with the seasons, or when available light changes because you move the plant to a lighter or darker location. When exposed to increased light, plants respond by lining up more chloroplasts so they can put to use a more abundant supply of light. When light is decreased, leaves let go of chloroplasts that are no longer needed.
A robust Boston fern basks in the reflected light from white walls and furnishings.
When deprived of sufficient light, plants naturally stretch toward the closest window.
These changes do not happen overnight. Rather, adapting to changing light levels is a gradual process, which brings us to what is called acclimatization. When a plant is moved to a place where light conditions are different from the place it was before, it immediately begins making changes in its chloroplast structures, and other cells get in on the act as well. If the plant is not receiving enough light, it may twist and bend toward the light source in order to reorient its solar collectors (leaves) so they can collect every ray. This process, called phototropism, is also evident when stems lengthen as a plant stretches toward light. Some plants respond more dramatically, by shedding light-starved leaves. Ferns and ficus are famous for their tendency to shed leaves in response to a radical reduction in their light supply.
On the other hand, if a plant accustomed to low light conditions is suddenly moved into bright light, its leaves may be so ill-prepared that they wither. Thin layers of chloroplasts are usually housed by thin leaves with meager moisture reserves. Houseplants can be damaged or killed when moved from dim to bright light if they are not given 2 to 4 weeks to adjust to the change — a common challenge when plants are moved outdoors for the summer (see page 291). Leaves that are scorched by sudden exposure to bright sun seldom recover from the trauma.
Keep these processes in mind as you discover or create the ideal light conditions for your plants. Finding the best spot in your house to grow a certain plant is a hunting expedition, but knowing the light preference of the plant, and where such light is likely to be found, simplifies the task. The light preferences of individual plants are given in the plant profiles in Parts 1 and 2. Below we will discuss using natural light from windows and supplementing natural light with various types of artificial fixtures.
Assessing natural light. Spaces near windows are logical places to grow houseplants. Natural sunlight includes a full spectrum of rays, and of course no electricity is needed to run a window. Large windows admit more light than small ones, but almost any window can accommodate some type of houseplant. Keeping windows clean is an easy way to maximize natural light. It also can help to trim limbs from outdoor trees and shrubs that block light as it enters your windows. If the light from unobstructed, squeaky-clean windows proves insufficient, you can easily add supplemental light. Similarly, excessive natural light can be filtered through a sheer curtain, making it more acceptable to both plants and people.
Get to know the compass orientation of your windows by watching where the sun rises (east) and where it sets (west). In North America, a southern exposure always offers the strongest light because the sun arcs from east to west from a slightly southern spot in the sky. The arc is lower in winter and higher in summer, so even indoors there is a remarkable seasonal difference in how much light comes through a south-facing window. As a general rule, it is best to reserve space near south windows for high-light plants.
In the Northern Hemisphere, the sun’s arc is much nearer to the southern horizon in winter, so north windows receive very little light. The sun’s arc rises in summer, so all windows receive more light.
Similar seasonal trends affect windows on the north side of your house. In summer, north-facing windows may provide enough light to grow low-light houseplants, but in winter few plants are satisfied with the weak light in a northern exposure. Yet there are exceptions. Many blooming houseplants need a cool rest in winter, which can coincide with low light conditions. If you have a room with a northern exposure that can be kept cool, at 55–60°F/13–16°C, it can become a valuable asset by providing space for resting cacti and other plants that need a cool, dry period of semi-dormancy. Should additional light be needed, you can use fluorescent fixtures (see also “Using Artificial Lights,”), which give off very little heat.
East windows typically get strong morning sun, while west windows are brightly lit from early afternoon until evening. Even low-light plants enjoy gentle morning sun, so east windows are often preferred places for plants that adapt to low to moderate light. Afternoon sun tends to be somewhat harsh and quite warm, so west windows are often good places for high-light plants that prefer warmer conditions.
Natural light from windows is always directional, meaning it comes from one primary direction. Plants respond by turning toward the light, often changing into a lopsided shape. To support good posture in your plants, make a habit of turning them a quarter turn about once a week. Plants grown in oblong boxes or dish gardens can be turned halfway, so that the front and back are given equal opportunities to bask in directional light.
Increasing interior light. Light from any direction becomes weaker as you move away from the window. Much of this decrease depends on the ability of interior walls to reflect light. White or light-colored walls reflect much more light than dark-colored walls, which are often said to absorb light. In rooms with dark walls, good plant-growing space is limited to 12–24 in/30–60 cm from the windowpane, while rooms with light-colored walls can accommodate larger plants, or plants placed more than 24 in/60 cm feet from the window. Mirrors hung so that they reflect light from windows can help illuminate any room.
In homes where good plant-growing windows are few, many plant lovers install a bump-out window with shelves in a south- or west-facing window, creating an ideal spot for houseplants. In addition to providing abundant light, such a window has the feel of a small greenhouse, and may help collect solar heat in winter that can be shared with the rest of the room.
A plant shelf, in which fluorescent light is maximized by reflective hoods, is a practical way to meet the light needs of a large collection of houseplants.
Using artificial lights. The ultimate way to increase interior light is to use supplemental lighting, which may work other magic for your home or office. Spotlights used to coax large plants to grow lush and full can be situated for maximum drama, and often make rooms look larger in the process. A shelf bursting with lush foliage that basks beneath a suspended light fixture becomes a refreshing indoor focal point. In your office, perhaps you can use a tall, linear floor lamp outfitted with compact fluorescent bulbs to transform a dull corner into a haven for air-purifying houseplants. When considering supplemental lights intended to benefit your houseplants, expect to be pleasantly surprised by the clean warmth they bring to any room.
There are many choices. Regular lightbulbs, called incandescent lights, can help supplement light a little, with two drawbacks. Incandescent lightbulbs give off heat, which may be undesirable for both you and your plants, and the light they provide is incomplete compared to natural light. Incandescent light is often called soft or “warm” light because it includes more red rays than blue ones. This is why it flatters human complexions. Unfortunately, many houseplants, particularly foliage plants, prefer light with good saturation on the blue-to-green end of the spectrum.
Even inexpensive under-counter fluorescent lights are useful for providing light to plants.
HISTORICALLY, LIGHT FOR PLANTS has been rated in terms of foot-candles. Strictly speaking, a foot-candle is the amount of light cast by a candle 1 foot away. Plants that adapt to low light will grow with only 100–300 foot-candles of light, those that need medium light need 300–600 foot-candles, while high-light plants need a minimum of 700–1,200 foot-candles. In the interest of comparison, sunlight at noon on a clear summer day is usually in excess of 10,000 foot-candles.
Your plants will usually let you know when they are receiving too little or too much light, but if you like, you can calculate foot-candles using a camera with a built-in light meter, focused on a white piece of paper in the spot you want to measure. If the camera shows an f-stop of f2–f4, with a slow shutter speed to match, the foot-candle rating is probably less than 400, or low light. An f-stop of about 5.6 with a shutter speed above 
second suggests 400–600 foot-candles, or medium light. High light would give an f-stop of 8 or greater, which translates as more than 700 foot-candles.
You can also use the simple shadow test to evaluate light. When the shadow cast by your hand is barely discernable, the site receives low light. A well-defined shadow indicates moderate light, while a sharp, high-contrast shadow is created in high-light conditions.
This is exactly what you get with fluorescent light. Fluorescent light is a little short in red light waves, which is why it seems a bit “green.” But compared to incandescent bulbs, fluorescent lights offer a broader light spectrum, the tubes are a bit more durable and give off less heat, and they are more energy efficient. New “compact fluorescent” bulbs (comprised of narrow, curved tubes) represent a huge advance in energy efficiency, requiring half the electricity of incandescent bulbs to put out the same amount of light. They also last much longer than incandescent bulbs. Compact fluorescent bulbs can be screwed into traditional lamps and light fixtures designed for incandescent bulbs, or they can be purchased as tubes that fit into tube-type light fixtures. In terms of the quality of light they provide, low heat output, energy efficiency, and long service life, compact fluorescent bulbs are well worth their cost, which is slightly higher than that of incandescent or traditional fluorescent bulbs.
When using artificial lighting, experiment with the distance between the light source and your plants. High-light plants respond well to having lights only 4–6 in/10–15 cm away, while plants that accept medium or low light thrive when the light source is 8–12 in/20–30 cm from the topmost leaves. Whenever it is practical, a reflective hood placed over the light helps capture and reflect light that would otherwise be lost to plants. Most light fixtures designed for plants include a hood. When using an under-cabinet-type light fixture, painting the mounting surface bright white has the same effect as a reflective hood.
Plants that have been struggling to make do with too little light often respond dramatically to supplemental artificial light. Once a fixture proves its worth, you will probably want to put it on a timer, so that the lights are turned on and off at regular times each day. Twelve to fourteen hours of continuous light is best for most houseplants, which also need regular periods of darkness. Some blooming houseplants will not set buds unless they are exposed to 12-plus hours of continuous darkness. See “Understanding Photoperiod,” for more information on handling light-sensitive plants.
High-intensity lights. Commercial growers, and some plant collectors, use special fixtures called high-intensity lights to simulate exposure to strong sunshine. Often abbreviated as HID lights (“high-intensity discharge”), these fixtures are costly and may require special wiring to accommodate the draw they make on electric circuitry. They are also not very pretty, and most require a ballast box to boost the power supply going to them. Still, if you develop a passion for cacti or other plants that need very bright light, eventually you may want to invest in HID fixtures.
There are two general types — metal halide and high-pressure sodium. Metal halide lights emit strong light at the blue end of the spectrum, so they are often used to encourage leafy growth of young plants. High-pressure sodium lamps do a better job of delivering red wavelengths, which encourage strong flowering. In commercial greenhouses, growers may use metal halide lights when blooming plants are young, and switch to high-pressure sodium lights when plants enter their flowering phase.
Both types of high-intensity lights are available from companies that provide equipment for hydroponic horticulture, which is the practice of growing plants in nutrient-enriched water that is continuously circulated around the plants’ roots. Increasingly, these companies also offer compact fluorescent fixtures designed for plants, which are quite satisfactory for most houseplants. See Resources for a list of suppliers.
Use a wheeled dolly to move very large houseplants, such as citrus trees or hibiscus. Extending the base of the dolly with a piece of scrap plywood will keep the plant from toppling in transit.
See also Acclimatization, Insect Pests, Light, Wind
The most traumatic move a houseplant will ever make is its move to your home, so newly adopted houseplants should always be given special care. In the weeks prior to this move, they may have been shifted from greenhouse to truck to retail store, so they may already have been exposed to temperature or moisture stress. Whenever possible, choose plants that appear to have settled into the place where they are displayed for sale, which is usually evidenced by a little new growth. Make a mental note of the light and temperature conditions to which the plant is accustomed, and see if you can find a place with similar conditions in your home or office. It’s a good idea to keep new plants isolated from others for a couple of weeks, so that any pests that may have been hiding in the foliage have a chance to reveal themselves. If you want to go ahead and put the plant to work in its permanent location, inspect it thoroughly for the presence of unwanted hitchhikers.
Be careful when moving very large plants, which are often surprisingly heavy. If you need to move a large plant only a short distance, you may be able to tip the container diagonally and roll it to its new place. Don’t hesitate to get help with bigger moves, particularly those that involve going up or down steps, and make use of a rolling cart or dolly when moving your largest plants. Moving large plants when the soil is dry lightens their weight slightly. When broad plants must be moved through narrow doorways, angle them so you can bring them through bottom first, which usually results in fewer broken branches.
Indoor-outdoor houseplants. There are many houseplants that love to spend the summer outdoors, where warm temperatures and abundant light help support strong seasonal growth. Try to make this move an easy one by gradually acclimating the plants to increased light. Keep them in a very shady place for a week or more before shifting them to a spot that gets dappled or partial sun. Many houseplants should be kept in shade all summer. Outdoor shade is still brighter than most locations inside your house. However, a few plants (for example, hibiscus and miniature rose) bloom best when exposed to very bright summer sunshine. Make their transition from indoor light to sun as gradual as possible. Keeping plants in a wagon or on a wheeled cart that can be moved in and out of the sun quickly and easily will save you much time and worry.
The top of a shady stone wall serves as a seasonal resort for plants that enjoy spending part of the summer outdoors.
As you choose outdoor locations for your plants, look for spots that are protected from wind. Houseplants are accustomed to still air, and twisting winds can quickly cause serious damage. Large plants can be dashed to the ground by wind, and heavy rain can be equally devastating. Covered sections of decks and patios are often better places for houseplants than locations that are open to the elements. If you do place houseplants where they will be rained upon, be sure to check the drainage trays following heavy rains, and dump out all accumulated water.
As days become shorter in late summer, plants will naturally adjust to less light, but it’s still a good idea to move them to a very shady location for a week before bringing them indoors. Tropical plants should be brought indoors before nighttime temperatures dip below 55°F/13°C, but some plants, such as azalea, holiday cactus, and kalanchoe, benefit from staying outdoors through the short, cool days of autumn. However, hardy bulbs that are being forced into bloom are the only house-plants that can be left outdoors in freezing weather.
Every houseplant grower can recall a day when a sudden cold snap caused them to rush to get plants back indoors in one fell swoop, but ideally this should be a well-planned operation. Some plants will need repotting because they have responded to outdoor warmth and humidity by producing abundant new growth. Subject all plants to the checklist above, and take appropriate measures to fix any problems.
After moving a plant indoors, or when it is simply moved from one location to another, you may need to adjust your watering practices. Reduce watering a little after moving a plant, because it’s always better to let plants become slightly dry than to drown their roots with too much water. In addition, watch for signs that the plant is getting too much or too little light. The retention of good leaf color or the appearance of new growth are signs that the plant has made any needed adjustments and is satisfied with its new home.
Each part of a plant has a special job to do, and when they all work together as they should, you have a healthy, happy houseplant. Use the drawings on pages 294–297 to become familiar with common plant parts, including roots, stems, leaves, and flowers. Understanding various plant parts will deepen your appreciation for your plants and eliminate much of the mystery from routine maintenance activities. It will also improve the skill with which you care for your plants, and simplify complex tasks such as repotting and propagation.
Fibrous roots may spread through the soil to form a thick network of thin fibers.
A taproot is a thick, vertical root that extends downward beneath the plant’s crown. Smaller roots spiral outward from the taproot, which is often somewhat fragile.
Storage roots come in several forms, including bulbs, corms, tubers, and rhizomes.
Spreading roots such as stolons and rhizomes often include buds that grow into new plantlets.
Stems attach to the roots at the plant’s crown. The places where leaves attach to the stems are the nodes. The leaf bud at the tip of the stem is the dominant bud. Nodes further down the stems often include latent buds, which begin to grow when the dominant bud is removed.
Leaves attach to the stem, or to the plant’s crown, with leaf stalks, or petioles. In some plants, the petiole also serves as a stem.
Nodes also may develop adventitious roots, which begin growing when they are in contact with damp soil.
Leaves receive moisture and nutrients, and transport energy synthesized by chloroplasts, through their leaf veins. Stomata are tiny pores in leaves that “breathe” by exchanging gases.
Simple leaves are singly attached to a stem or crown.
Compound leaves include several leaflets attached to a single petiole, or leaf stalk.
Bracts are modified leaves that frame the true flowers. Bracts contain less moisture than petals, so they often persist for weeks rather than days.
In some flowers, the bract is a fleshy spathe. The elongated finger-shaped structure inside the spathe is the flower.
A blossom or flower, sometimes called an inflorescence, is comprised of soft, fleshy petals that enclose the male flower parts (stamen) and the female flower parts (pistil).
Male flower parts. A filament attached to the base of the flower ends in an anther, which bears pollen. This apparatus is called the stamen.
Female flower parts. The ovary at the base of the flower is the chamber where seeds form. It is attached to the stigma, the organ that receives pollen, by a tube called a style. The complete female flower structure is called the pistil.
To defend themselves from leaf-eating predators, several houseplants are chemically equipped with toxic compounds that may taste extremely bitter, cause an acute burning sensation in the mouth, or trigger swelling of the mouth and throat when they are eaten by pets or people. People usually learn not to put these plants in their mouths instantly, but pets who are bored or too curious for their own good may not be trustworthy in the presence of some of these plants. You need not worry if you see evidence that a pet has casually played with the leaves of one of the plants listed below. Chances are good that during that play session, the plant will have taught the pet what it needs to know. However, if a puppy or kitten appears very sick after chewing one of these plants, your veterinarian will need to know which plant has caused the trouble, because the toxic compounds vary from one species to another.
See also Repotting
When a plant needs more space for its roots, it is shifted to a container only slightly larger than the one it was growing in before. This procedure is called potting up. When potting up, take care not to move a small plant into a very large container, which can lead to problems with root rot. When a plant is repotted into a container the same size as the one it was growing in before, it is called potting on, or simply repotting.
Many houseplants are so easily propagated that they can become your lifelong friends. It is also gratifying to propagate plants to share, and sometimes you may want to launch into a propagation project out of a sense of adventure. When you see roots emerging from stems looking for a place to go, or when you’re pruning off stem tips to improve a plant’s shape, it is fun to go to the next step and grow a new plant.
Understanding the botanical processes behind the transformation from stem or leaf to a nicely rooted new plant makes propagation less mystifying. In the course of normal growth, plants develop specialized cells that become roots, stems, leaves, and flowers. Along with these purposeful cells, plants lay down a safety cache of more versatile cells, which can morph into specialized cells should the plant’s welfare be threatened. An excellent example is what happens when you propagate a new plant from the base of an African violet leaf. The base of the leaf stem, or petiole, is stocked with cells capable of developing into roots and leaf buds, and if conditions are right, this is exactly what happens.
With all plants, the art of successful propagation involves coaxing these latent cells to action. The individual plant’s anatomy will suggest to you the best method to try; these anatomical features and the propagation methods that best suit them are discussed in detail in the following pages. Consult the plant profiles in Parts 1 and 2 as well to learn the best propagation methods for individual species. The six most common methods of propagating houseplants — rooting stem cuttings, rooting petiole leaf cuttings, simple layering, air layering, division, and seeds — are described in detail in the following pages.
None of these methods is extremely difficult, though patience is often required. And, although you may occasionally propagate a plant as an emergency measure to save its life, it is always best to get plants into the best possible condition before propagating them. If you want to propagate a plant that has been neglected, give it a few weeks of regular water, fertilizer, and appropriate light before beginning the propagation process.
As for timing, there are many exceptions, but spring is usually the best season to undertake propagation projects. Houseplants respond to the long, sunny days of spring and summer by producing new stems and leaves, so plants propagated in spring have the best opportunity to make fast, steady new growth. Propagate flowering houseplants when they are not in bloom, because plants in flowering mode are controlled by hormones that tell the plant to channel its resources toward the production of buds and blossoms, usually at the expense of new foliar growth.
Stem cuttings. Most plants that develop leaves attached to linear stems can be propagated by rooting 3–4 in/7.5–10 cm-long cuttings taken from the tips of the stems. You also can root sections of the stem other than the tips. This is often done with plants that develop canelike stems or that have stems liberally endowed with nodes, such as rosemary. Whether you are working with stem tips or stem sections, the places that will develop new roots and leaves are the nodes — the places where the leaves attach to the stems. Nodes contain a good supply of cells that can grow into roots if needed to ensure the plant’s survival.
The growth of these cells can be stimulated by plant hormones, called auxins, which are readily available in rooting powder. All garden centers sell rooting powder, usually packaged in small plastic jars. Stem cuttings that are set to root must quickly develop roots or they rot, and using rooting powder greatly increases the chances that the former, rather than the latter, will occur. With remarkably willing rooters, such as Swedish ivy, rooting powder is not necessary.
Rotting is also less likely if the cuttings are set into a medium that does not support the growth of fungi. Three such mediums are seed-starting mix, which is usually comprised of vermiculite and peat moss; plain perlite; or a half-and-half mixture of peat moss and sand (see page 314 for more information about these materials). A few plants prefer one medium over another, but most plants root equally well in any of the three.
The procedure for “sticking” cuttings is simple, but success is never guaranteed. It’s a good idea to stick more cuttings than you need, because some of them may fail when microorganisms enter the cutting. Most plants with soft, fleshy stems root best when the cutting is set to root immediately after being taken from the parent plant, but succulents and semi-succulent plants sometimes root better if the cut surface is allowed to callus for one to several days before it is set to root.
1. Cleanliness counts when handling cuttings. Wash your hands before filling small, clean containers with your medium of choice, dampen the medium well, and use a chop-stick or skewer to make holes for the cuttings.
2. Sterilize a sharp knife or pair of scissors by dipping it in boiling water for several seconds. Allow your cutting instrument to cool before severing a healthy stem just below a node.
3. Remove all but the topmost leaves from the cutting. Dip the cut end in water, then dip it in rooting powder, tap off the excess, and poke it into its prepared hole. (To avoid contaminating the rooting powder in its original container, pour out the amount you’ll need into a small saucer or cup, then dispose of any excess.)
4. Use your fingers to make sure the medium is in good contact with the stem.
5. For the first 2 weeks after setting any type of cuttings to root, enclose them in a plastic bag, container and all, and place them where they will receive no direct sunlight. A plastic bag or other humidity chamber is needed because, until they develop roots, the cuttings have no way to replenish moisture lost through the leaves. A translucent plastic bag held aloft with sticks works great for individual containers, or you can place several containers together in a small box and cover the top with a piece of plastic.
6. Each morning, remove the plastic and lightly mist the cuttings. In warm weather, check them again in the afternoon. Add water to the containers only if the medium appears to be drying out. Try to keep it lightly moist but not extremely wet.
In the third week, take off the plastic cover, but continue to mist the cuttings daily and keep them out of bright light. Remove and dispose of any cuttings that have obviously died (the stems will be black or shriveled). By the third week, you may see signs of new growth in some of the cuttings. If so, move them to a place where they will get a little more light, and begin mixing a small amount of fertilizer into the water used to replenish the moisture in the containers.
Most stem cuttings will begin to root in 3 to 4 weeks, but some plants may need 2 months or more before they are ready to be potted into regular potting soil. Use the appearance of new growth as your guide. You can also test for the presence of roots by gently pulling on the cutting. A bit of resistance means that roots have anchored the cutting in the rooting medium. Ideally, stem cuttings set to root in late spring will show obvious new growth by midsummer, at which time they can be transplanted to small containers filled with an appropriate potting soil. Rapidly growing rooted cuttings may need to be repotted again after a few months.
Cane cuttings. Cut the cane into pieces that contain at least one node, and plant them on their sides, barely covered with rooting medium. With several plants with canelike stems (for example, dieffenbachia), you can trim the top cluster of leaves and attempt to root it like a stem tip cutting, set 2 in/5 cm-long cylinders of cane to root, and also preserve the parent plant, which may develop new stems that emerge from the base of the cane left behind.
The latent nodes found on canes often can be coaxed into growing by planting small cane sections on their sides.
Petiole leaf cuttings. Some plants with very plump leaves that emerge from a central crown are best propagated from individual leaves. These include African violets, peperomias, rex begonias, piggy-back plants, and numerous succulents. The leaf stem, or petiole, is actually the plant part that develops roots. The procedure is similar to that used to root stem tip cuttings. Root several leaves, because not all of them will root successfully.
Remove petiole.
1. Choose healthy, medium-sized leaves rather than very large or very small ones. Using a sterilized knife or scissors, trim the petiole if necessary to make it 1–2 in/2.5–5 cm long. There is no need to trim succulent leaves, in which the leaf and petiole are merged into a single structure. However, you may need to let leaves taken from succulents dry overnight before setting them to root.
Plant leaf about ½ in/1.25cm deep.
2. Fill a clean, shallow container with dampened seed-starting mix, perlite, or a half-and-half mixture of peat moss and sand. Plant the prepared leaves diagonally, so the ends of the petioles are buried only about ½ in/1.25 cm deep.
3. Enclose the planted cuttings in a loose plastic bag to keep the cutting moist and humid, and place it in a warm place (75–80°F/24–27°C). Moderate light is usually best.
Check the cuttings daily to make sure the rooting medium has not dried out. If necessary, spray the cuttings and rooting medium with lukewarm water to maintain constant light moisture.
Petiole leaf cuttings usually root in 3 to 4 weeks. It then takes another month or so for small plantlets to form above the mass of new roots. When a plantlet has more than three leaves, it can be gingerly transplanted to a little pot, and the parent leaf may be snipped away and discarded. From this point on, plantlets will grow a little faster if a small amount of plant food is added to the water used to keep the growing medium moist.
Simple layering. Some plants readily produce roots (known as adventitious roots) at various places on their stems, most often in anticipation of the day when they find their way to a hospitable bit of soil, as might happen in the jungle if the stem were blown sideways in a storm, or perhaps stepped upon by a monkey. Spider plant provides an obvious example, with its habit of developing plantlets at the end of arching stems, each equipped with woody root buds. Other houseplants that have stems long enough to bend over and secure into a pot can reproduce in a similar way if given a little help. The big advantage of simple layering over rooting stem tip cuttings is that the cutting remains attached to the parent plant until roots have begun to grow. If you have tried rooting stem tip cuttings from a plant and failed, simple layering may prove to be a more successful method. Here’s how to do it:
Pinch off leaves attached to node.
1. Position a small container filled with dampened rooting medium in a place where a stem can be secured. Ideally, the part of the stem to be layered should be a node 2–3 in/5–7.5 cm down from the stem’s tip. Identify the section of stem that will be buried and pinch off any leaves attached to that node.
Secure the stem with a wire pin.
2. Wound the area right around the node by scratching off the outer tissue with your fingernail or by making a tiny cut that goes not quite halfway through the stem. This wound will cue the plant to mobilize into survival mode. Dust the wound lightly with rooting powder and secure it in place with a stone or piece of wire bent into a U. For the next few weeks, keep the buried section of stem lightly moist.
Sever the layered cutting from the parent plant.
3. After 3 weeks or so, you can sever the layered cutting from the parent plant and treat it as you would a rooted stem tip cutting, or allow the layered stem more time to grow roots. If the stem seems lazy at this task of growing roots, a second wounding of the layered stem, 1 inch above the soil, may help it get started.
Air layering. Like simple layering (described above), air layering coaxes a stem to develop roots while it is still attached to the parent plant. This method is most appropriate for upright plants, such as schefflera. Air layering is the best method to use when propagating upright plants that have become top-heavy or outgrown their space.
In air layering, rooting medium is attached to the plant stem, which is severed and treated like a rooted stem tip cutting after roots have begun to form. Although air layering takes time (usually 4 to 12 weeks), it is often surprisingly successful with tall, leggy plants. With some plants, you can air layer a primary stem, and after it is removed and transplanted to its own container, new secondary stems will emerge farther down the plant.
As with other propagation methods, the first step is to identify a place on the plant where latent root cells are likely to be present. Nodes where leaves attach are best, including the scarred areas left behind after old leaves are shed. However, do choose a spot with healthy green tissue over stem areas that have gone woody with age. And, because the stem will eventually be cut away as if it were a stem tip, it’s best if there are only a few leaves growing above the air layering site. A scant supply of new roots is incapable of supporting a large number of leaves.
1. Once you have selected the place on the stem where you want a new tuft of roots to grow, remove any leaves that are present.
2. Lightly wound the stem with a clean, sharp knife, cutting no more than a third of the way through the stem.
3. Dust the wound lightly with rooting powder and then wrap the wound with a “bandage” or dressing made from damp sphagnum moss (stringy, unmilled peat moss).
4. Cover it with plastic wrap and tape wrap in place with electrical or fabric bandage tape. You can also use clean potting medium packed into a small plastic bag firmly taped to the stem.
5. With either type of rooting pocket, leave a small opening in the top of the dressing where water can be added. Once the dressing is secure, add a few drips of water every few days to keep the moss or soil lightly moist.
6. Most air-layered plants begin producing roots in about a month, but wait until you see roots forming inside of the plastic to remove the dressing. When new roots are 2 in/5 cm long, cut the rooted section from the plant, remove the dressing, pot it up in clean potting soil, and treat it like a newly rooted stem cutting. Slowly increase light and fertilizer as new growth begins to appear. You are well on your way to having a robust new plant.
Division. Any plant that develops multiple growing crowns can be propagated by dividing the clump into smaller clumps. With most plants, division is a rather straightforward operation, consisting of teasing plants apart with your fingers and then using a clean knife or pruning shears to separate entangled clusters of roots. With others, such as tree philodendron, adjoining crowns are held close by thick, woody roots that must be sawn apart with a small saw or stout serrated knife.
Since it is important to injure as few roots as possible, the best way to do this is to submerge the plant in a tub or dishpan filled with lukewarm water, where old potting soil can be gently floated away and roots can be untangled while well lubricated with water. When roots are so tight and tangled that you can’t see what you’re doing, feeling your way along with the root ball submerged in water makes the job easier.
Begin at the outside of the clump, dividing off crowns that are far from the mother clump. If the roots are so tangled or tightly attached that they will not come apart, it’s best to grit your teeth and cut through the roots with a sharp serrated knife. As a general rule of thumb, it is best to divide a crowded clump into halves. If desired, the halves can be cut in half again. Pot up the divided clumps, planting them at the same depth that they grew in their original container. Expect to see some shriveling of leaves in the days that follow. Trim off these damaged leaves close to the base, and allow the plant a little time to adjust to its new independence. If the plant does not show good vigor after a couple of months, take it up from the pot so that you can remove bits of decayed roots that were damaged when the plant was divided, then repot.
When thick roots make it impossible to pull plants apart, cut through the root mass with a serrated knife.
When dividing plants, soaking the roots in a pan of water often makes it easier to separate tangled roots.
Seeds. Any plant that produces blooms eventually produces seeds, and seeds are the primary way that many houseplants propagate themselves when grown in the wild. However, because of insufficient pollination, seeds produced by indoor-grown plants may not be viable. And if the plants that produced the seeds are hybrids, the plants grown from the seeds will not be of the same quality and vigor of their parents. It is therefore not a good idea to save seeds from your own houseplants. However, you may want to try to grow some houseplants from high-quality purchased seeds.
This is usually a very slow process, and the vegetative propagation methods described above are always faster than starting from seed. Still, it can be done. Cacti, African violets, and even palms all can be grown from seed. Most young seedlings require very bright light, so do not attempt to grow plants from seed unless you have a greenhouse or a supplemental light fixture that can be suspended 2 in/5 cm from the tops of the plants.
The process itself is simple. Fill clean containers with damp seed-starting mix, and sow the seeds so they are covered to three times their diameter. Enclose the planted containers in loose plastic bags to create a moist, humid environment, and watch for the first emergence of tiny green sprouts. As soon as seeds germinate, move the containers to very bright light, and keep the planting medium lightly moist. The first leaves that emerge are often very simply shaped, but these seedling leaves soon give way to “true” leaves, which resemble those of a mature plant. When seedlings have more than three true leaves, gently transplant them to individual containers.
See also Cleaning, Grooming, Propagation, Repotting
You can prune a plant to remove dead or straggly branches, to improve the plant’s posture, or to rejuvenate it by forcing it to push out new growth. It is always best to prune when plants are actively growing, though light trimming can be done at any time of year. Most plants that have lost their shape or are holding onto unhealthy branches are candidates for some type of pruning.
Before you take up your pruning shears (or scissors, which often work equally well), take a moment to study the natural shape of the plant and how and where it develops new growth. Many plants produce new growth from the tips of stems and branches. The tip of the stem is called the dominant bud. Farther down the stem, there are usually latent buds located at the nodes — the places where leaves are (or once were) attached to the stem. As long as the dominant bud, or growing tip, is intact, it sends chemical signals down the stem that tell the latent buds to remain at rest. When the dominant bud is pruned, this signal is turned off, and latent buds spring to action and begin to grow.
When pruning cuts are made just above a node, new stems will emerge from the latent node.
Bearing this in mind, try to make your pruning cut ⅛–¼ in/.3–.6 cm above a node or other branch junction. To keep a plant bushy and full, prune some branches “hard,” cutting close to the base of the plant, and allow other branches to remain longer. Few plants benefit from a severe crew cut, though very vigorous houseplants such as geraniums and Swedish ivy respond well to aggressive pruning in the spring.
Most often, you will be doing light pruning to help plants grow into nicely balanced shapes or to snip off old blossoms from flowering house-plants. With many blooming plants, removing flowers as soon as they begin to fade encourages the plants to bloom again. If reblooming is not possible, trimmed plants will usually channel their energy toward the production of new leaves.
Some plants, such as Norfolk pine and most palms, cannot be pruned from the top, because they have no secondary buds. With these plants, keeping containers small helps control the size of the plants so pruning is not needed, except to remove unsightly old leaves. When plants become too large, it is best to find them a new home roomy enough to accommodate them.
Many people prune plants just before repotting them or prior to giving them a good cleaning. Be careful when watering pruned plants, because they need less water when they have fewer leaves to support. Finish up by cleaning your pruning shears or plant scissors so they will be ready for use when you next need them.
See also Containers, Drainage, Soil, Top-Dressing
When houseplants use up the soil and space in their containers, it’s time to repot them. Some plants can go years between repottings, while others need to be repotted at least once a year. You can tell if a plant needs repotting by looking for the following five symptoms that a plant is suffering from crowded roots or exhausted potting mix.
• LITTLE OR NO NEW GROWTH, which occurs when roots become so crowded there is no room for them to grow, or when the potting medium breaks down so the plant’s fine root hairs no longer have the physical structure they need to function properly. When plants are painfully rootbound, they often continue to produce new leaves, but the new leaves are small compared to the older ones.
• ROOTS ARE SNEAKING OUT OF THE POT, either through the drainage holes or by pushing the plant upward, so that it appears to be popping out of the pot. Some plants send anchor roots or aerial roots sprawling outside the container in a futile search for somewhere to go. At the same time, you may notice unusual yellowing of older leaves. While this is normal in some plants, and also can be a symptom of too little fertilizer, it is usually a sign that the plant needs more room around its roots.
• PLANT FREQUENTLY FALLS OVER because it has become top-heavy with foliage. A plant that becomes a chronic toppler can be repotted into a heavy container with a broad base, and perhaps can be secured to a stake as well. If this does not solve the problem, prune the plant or propagate it to reduce its size, and/or start over.
• PLANT IS CHRONICALLY THIRSTY, even when regularly watered. When plants require constant watering, it is usually because the roots are compacted or have outgrown the container. Repotting into a slightly larger pot usually solves this problem.
• SALT DEPOSITS HAVE FORMED inside the rim of the pot and on the surface of the potting medium, which do not disappear when the container is thoroughly flushed (see page 263). In this case, it is only fair to provide the plant with a root zone that is not contaminated by high levels of salt.
Check mature plants yearly for signs that they are in need of repotting. At other times, if a plant shows one of the above symptoms, remove it from its container and examine the condition of the roots. When you see mostly roots and very little soil in the bottom half of the pot, repotting is probably in order. If the roots appear to have plenty of room to grow, pop the plant back into its pot and don’t bother to repot.
The best time to repot any plant is when it is entering its most active season of new growth. For most houseplants this is spring, but some grow year-round, and others grow vigorously in fall or winter and rest in summer. Repotting is messy, so it’s great to be able to do it outside in spring, summer, or fall.
Sometimes you may have an accidental opportunity to repot a plant out of season — for example, if it gets knocked to the floor or mangled by a pet. It is also not unusual to be surprised by the amount of new growth plants produce when they are kept outside during the summer. When you bring a plant indoors in the fall, you suddenly realize that the plant deserves roomier quarters if it is to prosper during the winter months. When you must repot a plant out of season, disturb the roots as little as possible, because full recovery from the event may be weeks or months away.
Plants that have been troubled by disease or poor growing environments are seldom saved by repotting, which is often so stressful that it adds to a plant’s demise. Sometimes healthy plants respond to repotting by showing a fast spurt of new vigor, but it is also typical for repotted plants to sulk for a while as they adjust to their new container. Do not be alarmed if a plant sheds a few leaves in the weeks after it is repotted. This is a form of self-pruning, as the plant helps itself reach a good balance of roots and leaves. When given good care, repotted plants should recover completely within 2 months.
Step-by-step repotting. If possible, cover a table or other waist-high work surface with newspapers or plastic sheeting. You can repot plants sitting on the ground, but the project will be easier on your back if you can work on a raised work surface. If you have trouble lifting heavy containers, get help (see “Two-Person Repotting Jobs”). No plant is worth a permanent orthopedic injury.
1. Prepare plants to be repotted by thoroughly watering them a day or two ahead of time. Water again just before removing the plant from its old pot, because water acts as a lubricant, which is much needed when roots are tightly bound in the container.
Knock plant against hard surface.
2. Tap the container to loosen the plant. If the plant can be picked up, you can knock the pot sharply against a table edge or other hard surface. With very large pots, it’s more practical to tip the pot and knock against the high side with a rubber mallet, knife handle, or other blunt object. Regardless of the pot’s size, make repeated blows to all sides of the pot. The idea is to break adhesions that often develop between roots, old potting medium, and the inside surface of the container. Pliable plastic pots can often be smashed slightly to squeeze the plant from its moorings.
3. Lay the plant on its side and see if it will jiggle free without your having to pull hard on the main stem (always a no-no). If it is still stuck tight, use a knife to cut around the inside of the pot, the same way you might loosen a cake from a pan. Next, try to push the plant out from the bottom by poking upward through the drainage holes with a pencil or screwdriver. If it still refuses to budge, your only option is to break the pot. To break a plant out of a clay or ceramic pot, tap pot with a hammer until it shatters (save the pieces to use as drainage material). Thin plastic pots can be cut open with heavy-duty kitchen shears or a utility knife.
Use a knife to cut around inside of pot.
Root prune.
4a. Take a good look at what you have. If the roots form a solid mass, see if you can tease out a few that have wrapped into a tight spiral, and shorten them to the dimensions of the pot with a clean knife or pruning shears. This is often best done in a tub of water, or with the help of a hose and a gentle stream of running water. As you work, snip off any roots that appear black or dead, as well as those that unfurl into very long strands. There are exceptions, but most plants can be relieved of a quarter to a third of their roots as they are repotted. Don’t worry about cutting the plant off at its knees, because root-pruned plants often rebound dramatically once they have settled into a new supply of fresh, clean potting medium.
Trim plant to a cube.
4b. Alternatively, instead of trying to untangle the roots of houseplants that develop a dense network of fine, fibrous roots, remove the plant from its pot and stand it on a solid surface. Then use a sharp, serrated knife to slice four ½-inch-thick slabs from the sides of the root mass, so that it is trimmed into a cube. Repot into the same size container or a slightly larger one.
5. Place at least 1 in/2.5 cm of fresh, moist potting mix in the bottom of the container, or line the bottom of the container with broken crockery or pebbles (see “The Drainage-Layer Controversy”). Set the groomed plant in the pot so that it will be planted at the same depth in grew in its previous container. Fill the space between the edge of the root mass and the container with potting mix, and then use a table knife or chopstick to gently press the soil inward toward the plant’s roots.
Repot plant at original depth.
6. Add more soil, and tamp the container on a firm surface to help settle the particles in place. As long as the potting soil is nicely moist when you repot a plant, it is best to wait a few days before giving it a thorough watering. This delay in watering gives wounded roots a chance to wall off their injuries, and signals healthy roots to spread outward in search of water.
Add soil.
A few weeks after repotting, check the plant to look for spaces that may have developed between the edge of the pot and the soil by poking your finger into the potting mix. If needed, add a little fill soil to the top of the pot, but be sure to leave at least .5 in/1.25 cm of free space between the top of the potting mix and the rim of the pot.
See also Containers, Repotting, Watering
The phrase “potting soil” is convenient yet misleading, because good potting soil for house-plants contains little, if any, actual soil. Instead, it is a mixture of growing media intended to do all the things soil does, without soil’s negative side effects. Like soil, the medium should anchor the plant, provide particles to which tiny root hairs can cling, retain moisture until the plant needs it, yet not stay so wet that fungi and bacteria build up and cause roots to rot.
You cannot dig such a substance from your yard. True soil is made up of very small particles that are teeming with microorganisms. In the secret world of outdoor soil, these microorganisms form a dynamic community regulated by changes in temperature, moisture, the movement of earthworms and insects, and the constant inflow and decomposition of various types of organic matter. Conditions in containers kept indoors are much less lively, and if problem-causing microorganisms become established, there is no way for beneficial ones to gain entrance to set things right. This is why houseplants need special potting soil made of materials that naturally suppress soil-borne diseases and that have been further processed to rid them of microbial contaminants. Of equal importance is the texture of potting soil, which is noticeably light and fluffy compared to the soil outside your front door.
What is in the bag labeled “potting soil”? Ingredients vary from one brand to another, but most are blended from peat moss, composted bark or other plant material, and sand or perlite (see pages 315-16). They also may include shiny particles of vermiculite, and most have had their pH fine-tuned with lime (ground limestone) to bring it into the normal range. Many also contain small amounts of fertilizer to get plants off to a good start, but don’t choose a potting soil based on its fertilizer content. Instead, look for dark color, a spongy texture, and little or no odor. You can easily provide plants with fertilizer on an as-needed basis.
These days, potting soils are better than they have ever been, so it is easy to satisfy your plants’ need for good soil. The best potting soils are packaged in plastic bags with zipper-type closures, which helps keep them moist while keeping out unwanted microorganisms. After trying several brands, most houseplant growers settle on a favorite. Nationally marketed brands are usually safe bets, but you may get equal satisfaction with a “value” brand that costs less. If you keep only a few houseplants, a good all-purpose potting soil will probably meet your needs quite nicely. Buy no more than you think you will use in a few months, because opened bags of potting soil can become contaminated with microorganisms while also posing storage problems.
Unfortunately, even the best potting soil does not last more than a couple of years after it is put to work in a pot. Organic matter breaks down, minerals are taken up by plants, and the medium’s ability to do its job gradually deteriorates. This is why plants need periodic repotting even when they have not outgrown their pots. As for your old, used potting soil, throw it outside in your garden, or if you have no garden, dump it in a bag and give it to someone who does. When potting soil has been used up or worn out by houseplants, it can serve a second tour of duty in outdoor beds, where millions of microorganisms know exactly what to do with the threads of root and holdout tidbits of bark present in tired potting soil.
Making adjustments. Some houseplants prefer or require potting mix that meets their special needs. Details on what to look for in specialty potting mixes for African violets, bromeliads, cacti and succulents, orchids, and palms are discussed in the prefaces to each of these plant groups in Parts 1 and 2. However, it can be interesting and rewarding to create specialty potting mixes yourself by changing the balance of the materials in the mix. You may also need to adjust the content of all-purpose potting mix to help a plant that stays thirsty, hungry, waterlogged, or just plain unhappy despite attentive watering and feeding. Become familiar with the following six soil amendments, and you will be ready to tailor potting mixtures to please plants in need of special attention.
PEAT MOSS. Harvested from bogs in Canada, Michigan, and a few other places, peat moss is made up of very small fibers that have a remarkable talent for taking up water. Peat moss also suppresses many types of fungi that can cause roots to rot. On its own, peat moss has an acidic pH, so it is a good addition to potting soil intended for use with azaleas, gardenias, and other plants that prefer acidic soil conditions. African violet soils often contain liberal amounts of peat moss (with lime added to offset its acidity) because of its moisture-holding talents. And the fine texture of peat moss makes it a valuable addition to seed-starting mixes, which are excellent for potting up newly rooted cuttings. On the down side, when a peaty soil dries out it can be difficult to remoisten (see “Rehydrating Parched Plants,” on page 328). Before peat moss is packaged for sale or blended into potting soil, it is pulverized into a coarse brown powder. Unmilled peat moss, called sphagnum peat moss, is fibrous and stringy. When adding peat moss to another potting medium, be sure to moisten it first by mixing it with an equal measure of lukewarm water.
COMPOSTED PLANT MATERIALS. As you run your fingers through moist potting soil, and especially when you repot a plant grown at a nursery, you will probably encounter chunks of bark, bits of sticks, or other pieces of barely recognizable plant material. Although the outside of these tidbits will be black from natural decomposition, they are far from gone, which is good. The coarseness of these hard pieces aids drainage and helps prevent compaction, ensuring that plants enjoy plenty of air around their roots. There are environmental advantages, too. Most composted plant material begins as recycled waste from lumber and food-processing industries; in addition, it may include composted leaves collected from the yard.
Nurserymen like using bark-based mediums because of their excellent drainage and low cost. Many plants like them because they break down slowly and mimic soil conditions in crevices between tree branches — the native niche of many bromeliads and orchids. Naturally, specialty potting mixes for these plants include abundant composted bark. In regular potting soil, a very dark black color often indicates the presence of composted plant material.
SAND. Compared to other types of soil particles, grains of sand are quite large, so water flows quickly through soils that include plentiful sand. Coarse sand has long been used to create potting soils that drain quickly. The trade-off is that sand cannot retain moisture well, so a very sandy mix will dry out fast. This is a plus for cacti and other plants that prefer moisture in brief gulps, so sand is often added to soils blended for cacti and succulents. Palms and other plants originating along seashores, such as screw pine (Pandanus), also respond well when grown in a sandy mixture. Indeed, whenever you suspect that a plant is suffering from poor drainage or needs drier root conditions, amending the soil with sand is a good first step. A half-and-half mixture of peat moss and sand also makes a fine medium for rooting stem cuttings. For all uses, be sure to use sand that has been washed to remove salt and other impurities, such as sand packaged for use in aquariums. Sand used in children’s sandboxes also may be used, though it’s a good idea to give it a quick rinse in a bucket of fresh water before mixing it into potting soil for your plants.
PERLITE. In place of heavy sand, many potting soil manufacturers improve the drainage of their mixes by adding perlite — the small, white puffs that resemble broken pieces of popcorn. Perlite is made from a naturally occurring volcanic rock that pops when it is quickly heated to 1600°F. The popping process riddles each perlite piece with thousands of tiny air spaces, which makes it possible for perlite to take up and release water very quickly. Perlite is chemically inert, with a neutral pH (7), so it has no chemical influence on soil beyond regulating water and oxygen. When adequate nutrition is provided, plants can grow in 100 percent perlite, and it makes a great medium for rooting cuttings. Many potting soils include perlite, and those created for cacti and succulents often contain an extra helping. Small bags of perlite are widely available at garden centers. Many houseplant growers keep some on hand for rooting cuttings or lightening up soil that seems too heavy for certain plants.
VERMICULITE. Like perlite, vermiculite is made from naturally occurring mineral deposits that are mined, crushed, and then heated to the popping point. Vermiculite shares perlite’s water-handling talents, so it helps hold soil moisture while improving drainage. Vermiculite mixes very easily with peat moss, and this mixture is the basis for most seed-starting mixes. Always dampen these mixes — or pure vermiculite — when handling it, because some vermiculite contains small amounts of asbestos-like particles, which should not be inhaled. These particles, if present, are not likely to become airborne unless they are quite dry. Using moist vermiculite to root cuttings and start seeds, and mixing it into potting soil to lighten its texture, pose no health risks.
MINERALS. As a finishing touch, most potting soils include a dusting of various minerals, such as lime, gypsum, or rock phosphate. Lime (ground limestone) raises the pH of mixes that are too acidic and provides plants with slow-release calcium. Gypsum and rock phosphate also serve as very slow-release fertilizers, so they are a welcome addition to many potting soils. As a casual house-plant keeper, the only mineral amendment you might want to keep around is a little lime, especially if you have heavily fluoridated water or mix your own peat-based potting mixes. A pinch of extra lime in a pot helps keep the pH high, which in turn helps some plants cope with the uptake problems associated with chemically tainted water. Never add lime to soil used for plants that like acidic soil conditions, such as azaleas, gardenias, and most ferns. In rare instances, however, a batch of potting soil may be so acidic that plants have trouble taking up nutrients. If plants fail to grow well after they have been repotted and do not respond to an increase in fertilizer, you can try giving them a drench with lime water, made from mixing a teaspoon of powdered lime into a quart of water.
Insects that feed by sucking plant sap, such as aphids and scale, excrete a sticky substance called honeydew, which in turn serves as an ideal home for dark-colored sooty mold. Sooty mold is often mistaken for fungus, but there is a major difference in that sooty mold does not invade leaf tissues. It can be removed using a soft cloth dipped in soapy water, and once leaves are clean they usually appear perfectly healthy. Sooty mold can occur on either side of a plant’s leaves, or on both sides. When a plant shows patches of sooty mold, be sure to check for the presence of the pest that created the honeydew and take appropriate measures to bring it under control. In some situations, the sucking insect that began the problem cycle is gone by the time sooty mold develops on plant leaves.
Just as newly planted trees often need stakes to hold them straight until their roots are able to function as firm anchors, so it is with house-plants. A stake can be used as a temporary prop for a plant that insists on falling over, or it can be a permanent fixture in the pot of a vining plant. You can also stake and train a plant to alter its shape. Topiary, for example, trains plants to assume the shape of their “stake,” which is usually a wire form filled with moss. Some plants can be trained to grow into tree forms, called standards, which are comprised of a lean, upright main stem topped by a mass of foliage. Training guidelines for topiary and standards are discussed below.
Routine pruning and grooming may be all your plants need to keep them looking handsome, so you may never venture into involved plant training projects. But do go to the trouble of training naturally floppy plants, such as abutilon, and vines that are willing to grow on pillars — the best way to obtain a plant with a strong vertical posture. Vertical plants take up small footprints and offer tremendous versatility in interiorscapes, where they combine beautifully with other plant forms.
Simple staking. Plants that flop over may be stressed by too much or too little light, or they may emerge from the repotting process without sufficient roots to hold them upright. In either case, their postures can be improved by tethering them to a stake for a few weeks. Any type of stake will do, from a slender stick or piece of bamboo to a length of stiff, heavy-gauge wire. A single stake should suffice if only a little support is needed. Loosely secure the plant to the stake using soft string, twist ties, or a large paper clip bent out into an S shape that can be looped around the stake and the plant. Tight bindings can girdle stems, so it is better to use multiple loose attachments as opposed to a single tight one. (See at A.)
Plants with several floppy stems are better held up with a cage made from several slender stakes slipped inside the edges of the pot, which can be netted together with string, twine, or pliable wire. However, plants that require this level of support for more than a few weeks after repotting probably need a permanent support, or they may have grown so top-heavy that they are more in need of propagation than support. It is also possible that they might look better if allowed to cascade out of a hanging basket. (See at B.)
A simple stake to which a plant is loosely tied will quickly improve its posture. Whenever possible, install a stake as part of the repotting process.
Twining plants such as jasmine will twist around their support, which can be as simple as a tripod of bamboo stakes secured together at the top with jute or wire. Or, make a hoop with heavy-gauge wire, with each end of the wire pushed down into the pot, or use green, pliable saplings less than .5 in/1.25 cm inch in diameter to create a twig trellis for twining vines. (See at C.)
After repotting a floppy plant, you can make a temporary support cage by tying together stakes pushed inside the edges of the pot.
Semi-climbers such as pothos, climbing philodendron, ivy, and tree ivy (Fatshedera) slowly anchor themselves in place with strong aerial roots when provided with a support material that retains moisture, because the plants respond to the moisture by more vigorously producing aerial roots. Moisture-retentive osmunda posts or moss-filled wire posts are widely available at craft and florist shops. (See at D.)
The stakes, trellis, or post will become a permanent part of a vining plant, so try to begin training at a young age. Install the post slightly off center in the pot, and attach the plant to it with pieces of wire or florist tape. Plants more than 12 in/30 cm tall may need to be attached at several points. Aerial roots are most likely to emerge from nodes, so these are the best places to create close contact between the plant stem and the post. You can further encourage aerial roots to grow by misting the attachment points with water every few days.
After the initial attachment of the main stem is complete, new lateral stems may emerge. You can shorten these by pruning back the tips, or you can secure them to the post. Lateral stems that pop out high on the plant can cause it to be top-heavy. To keep the plant from falling over, top it back or trim the lateral stems off entirely. As a general rule, vining and climbing plants should be pruned and trained into a pyramidal shape, which ensures that all parts of the plant receive abundant light.
Twining vines need little help to scramble up a stake, or to wind around a moss-filled topiary form.
Plants that attach themselves to a post with aerial roots often need encouragement. Tape or wire them in place, and provide moisture to help the roots attach themselves to the post.
Topiary training. The art of training plants to grow into the shape of a special form, called topiary, can be practiced with several houseplants, including creeping fig, small-leafed varieties of English ivy, and varieties of rosemary that develop long, pliable stems. Craft and floral shops sell special topiary forms, which may be shaped like animals, cones, or wreaths. The forms are made from wire mesh stuffed with sphagnum moss; you can also make one yourself if you want to create a uniquely shaped topiary.
Before beginning a topiary project, soak the form in water for 30 minutes to make sure it is completely hydrated. Start topiary training during routine repotting, or buy new plants especially for the project. Large topiary forms or wreaths usually are sculpted from two or more plants situated at opposite sides of the form.
Once the plants and the form are settled into the container, attach primary stems to the form using fine wire. Prune off stems that show little promise for your training plan, but do not weaken the plants by trimming them too aggressively. Set the container in a hospitable spot and allow it to grow for a few weeks. Spritz the form with water every day or so to keep it lightly moist.
Every 4 to 8 weeks, work your topiary by removing old training wires that are no longer needed, installing new ones, and trimming off errant, untrainable stems. Use bright light to help energize growth spurts following each training session. Beginners often enjoy great success with topiary, but as with all creative arts, practice and patience lead to more pleasing results.
Training a vining plant onto a topiary form is not difficult, though it is important to trim the plant often, and to provide growing conditions that encourage rapid growth.
Year 1: The first phase of creating a standard form is to train the plant to grow very tall and straight, which usually requires the help of a stake.
Year 2: When the plant’s trunk is strong enough to provide good support, prune the top of the plant to the shape you want.
Standards. A few houseplants, such as rosemary, can be trained to grow as standards. The process requires 2 years or more, and commercial growers use varieties with growth habits that make them especially responsive to this type of training.
Year 1. Training begins by encouraging the plant to grow stiffly upright. With the plant’s main stem secured to a stake, pinch off any lateral branches that attempt to grow from the lowest third of the plant.
Year 2. Remove any remaining lateral stems, and tip back stems at the top of the plant to a few inches long.
As the remaining stems fill out, the standard form is finally attained. However, even the best standard forms are usually not sustainable for more than one or two seasons. Eventually, the topknot becomes too heavy for the main stem, or it thins out as buds held in reserve in latent nodes are used up. Enjoy it while you can.
See also Humidity
Where space is limited (for example, in an office cubicle or a small apartment), you can enjoy the companionship of plants with no risk of mess by growing them in a terrarium. Nestled into a goldfish bowl or little aquarium tank, a comely collection of plants will thrive with very little care. Terrariums that have an opening through which air can circulate need small amounts of water added from time to time, while those that are completely closed often can go months without watering. And because the conditions within terrariums are naturally moist, they make it possible to grow filigreed ferns and other dainty plants that require very high humidity levels.
About terrariums. In 1842, Dr. N. B. Ward of London published a book on what he called The Growth of Plants in Closely Glazed Cases. Today we know these as terrariums. Rather than botanical curiosities (which coincided with the invention of flat plates of glass), terrariums are most practical for growing small plants that require humid conditions in otherwise dry indoor environments. And because they require scant watering and feeding, terrariums are ideal for forgetful gardeners. The fluorescent lights in windowless offices usually provide enough light to satisfy high-humidity terrarium plants, which are often native to the damp conditions of the jungle floor.
A terrarium can be a completely enclosed glass jar or box, such as a fish tank, or you can use a fishbowl or large brandy snifter with its top left open. Open terrariums seldom have problems with disease since air circulates around the plants’ foliage, but they need to be watered more often than enclosed terrariums. This is easily done by spritzing plants with water from a small spray bottle. If an open terrarium must be left unattended for a long period of time, covering the opening with glass or plastic will prevent loss of moisture.
Very small plants, which are often quite inexpensive, make fine members of a terrarium community. You can buy plants at floral shops or garden centers, or order unusual species from online or mail-order nurseries. Depending on the size and shape of the container, you may want three, five, or several more plants. Before planting them in your terrarium, experiment with arranging them on a tabletop. Terrariums are usually viewed from one side, so it’s best to place the tallest plants to the rear, with smaller plants in front of them. Include one variegated plant, but let various shades of green provide most of the color in your terrarium. The differing leaf textures of the species you choose will provide plenty of visual interest. As you plan placement, make sure that the leaves of plants do not actually touch the glass, which can cause them to stay wet for long periods, leading to problems with disease. Use a small pair of scissors to snip off any leaves that are less than perfect.
Like an enclosed miniature jungle, terrariums showcase small plants that thrive under very humid conditions.
Planting a terrarium. Most of the discount stores sell all the materials you need for your terrarium. In addition to a container, purchase a package of clean pebbles and another of charcoal, which you will find among aquarium supplies. In the garden department, buy a small bag of sphagnum peat moss and a fresh, unopened package of potting soil. Starting with clean, packaged materials is the best way to avoid introducing fungi that can cause diseases in the artificial world you are creating.
1. Wash the container with clean, soapy water and dry it thoroughly. Place a .5 in/1.25 cm layer of pebbles in the bottom of the container, followed by .5 in/1.25 cm of aquarium charcoal. Soak the sphagnum moss in a bowl of water for a few minutes. Squeeze out the excess water and then carefully place the sphagnum moss over the charcoal. The moss will work like a filter, keeping the soil from seeping down into the pebbles.
2. Use a ladle or small cup to place about 2 in/5 cm of moist potting soil over the moss. Try not to get soil on the sides of the container.
3. Set your plants in place, then use a fork, chopstick, or long kitchen tongs to nudge them into their permanent positions.
4. Use a wine cork stuck onto the end of an ice pick or the back of a spoon to tamp the surface of the soil, thus ensuring that all roots are firmly in contact with soil. For a touch of whimsy, add a few small stones or perhaps a figurine of a frog or snail if you wish.
5. Use a spray bottle or mister to rinse off any soil that has stuck to plant leaves and to lightly dampen the potting soil. Cover the terrarium for a day, then mist or spritz the plants again. The second spraying should provide ample water for an enclosed terrarium, but open containers may need a little more water. Watch the plants for signs that they need more water, but err on the side of dryness. Especially in an enclosed terrarium, it is very difficult to get rid of too much water.
Every 2 to 3 weeks, check your terrarium to see if it needs water, which is easily supplied by spritzing plants with a spray of water. Two or three times a year, add a small amount of all-purpose houseplant food to the water, mixing it at half the rate recommended on the package. Groom plants periodically by snipping off failing leaves with a small pair of cuticle scissors. Allowing withered foliage to remain in the terrarium can lead to problems with disease.
Beyond overwatering, the only other problem you might have in a terrarium is overheating. Never place a terrarium in direct sun or near appliances that give off heat. If the terrarium’s light comes from a window, rotate it weekly so that all plants get a chance to respond to directional light. Should some of the plants in your terrarium grow too large, you can either cut them back or take them out, pot them up, and install small replacements in the terrarium. Changing the scene is part of the fun of working with a terrarium. Sometimes switching out one plant is all that is needed to bring new life to a composition that has visually gone stale.
When plants grow so large that repotting is impossible, or they have a cascading growth habit that will be ruined by handling, you can top-dress the soil instead of repotting the plant. It is usually more practical to top-dress than to repot large, woody plants such as Norfolk pine or weeping fig, and you may also opt to top-dress tall, columnar cacti and big palms. To top-dress, allow the soil surface to dry, then use a table fork to loosen the top inch of potting medium. Remove it with a tablespoon. You may be able to dig a little deeper just inside the rim unless you have encountered a tight ball of roots. Use the fork to make shallow perforations in the soil and roots below where you have excavated, then refill the container with fresh, high-quality potting soil. Plants that are not repotted should usually be top-dressed once a year, preferably in spring.
When top-dressing, loosen the surface soil with a fork, and then remove it with a spoon. Be sure to perforate the excavated surface before replacing the top layer with fresh potting soil.
See also Drainage, Fertilizer, Humidity
Though all houseplants need water, they are all a little different in this respect. Species vary in how much water they must take up and push to their leaves, and whether they prefer steady or fluctuating moisture levels around their roots. Containers and soils introduce more variables, but the most important factor is the air. It seems reasonable to expect that actively growing houseplants that are enjoying the warm temperatures of summertime would need more water than plants resting their way through winter, but this is not necessarily true. Indoor air in winter is often so dry that some plants need as much water in January as they do in June.
The bottom line is that every plant is an individual where watering is concerned. Getting to know the drinking preferences of each of your plants and satisfying them with your watering practices is one of the fundamental satisfactions of growing indoor plants. See the individual plant profiles in Parts 1 and 2 to learn about each of your plant’s watering needs.
Rhythms of watering. The lingo used to describe routine watering practices includes these phrases: “lightly moist,” “moderately moist,” and “allow to dry out between waterings.” These are general tendencies, open to interpretation by different plants.
LIGHTLY MOIST. This first moisture level means that the plant benefits from soil that is never truly wet yet never completely dry. To achieve this result, you simply provide water frequently and take care to distribute it evenly in the container. Many plants that come from forests — both tropical and temperate — like to be kept lightly moist at all times.
MODERATELY MOIST. Plants that need moderate moisture often are fast growers with high light requirements. They include most of the indoor plants that produce beautiful flowers and a few robust foliage plants as well. Although somewhat demanding, these plants provide color and drama, and they often go into an annual recovery period of slow growth or dormancy when they need little or no water. The challenge is to provide ample moisture without getting carried away, because even plants that need abundant water can develop root rot or other problems if they are watered too much.
ALLOW TO DRY OUT BETWEEN WATERINGS. Many plants with succulent leaves or stems love to exercise their talent for hoarding moisture when water becomes available the same way they might if they were living in a climate where rains were few and far between. These are the plants that benefit from brief periods of dryness, and they often like their wet intervals to be short lived too. But all succulents are not alike in this respect, so it’s best to pay attention to your plants’ responses to watering and fine-tune your practices to please them. Aloe, for example, seems to thrive on moisture extremes, while holiday cactus likes consistent moisture in summer and drier conditions in fall and winter.
Gauging soil moisture. The most common way to check the moisture level in plant containers is to wiggle your finger into the soil, up to the first knuckle, and decide if the soil feels moist about an inch below the surface. Even professionals use this method, along with other low-tech tricks such as tipping the pot to see if it feels heavy or light. But the finger method has its limitations. You can’t tell how much moisture is present deep in the container, and you know nothing about the most difficult area to water, the center of the plant’s root mass. To find out how much water is present in those areas, you can use a probe or meter (which are not always reliable) or assess the container’s weight.
There is always some guesswork involved in plant watering, but the finger method combined with regular weight checks should get you started in the right direction. Of course, the most important thing is to pay attention to your plants. Either underwatering or overwatering can cause a plant to droop, as can incomplete watering, in which only part of the root mass receives moisture. To prevent this problem, learn to water your plants from both the top and the bottom.
Top and bottom watering. The best way to water most plants is from the top, by slowly pouring water from a bottle or watering can around the plant’s crown until water drips out through the drainage holes in the bottom of the container. There is always a possibility that water applied this way will run over the top of the soil, down the insides of the pot, and then out the drainage holes in the bottom. When this happens, the plant’s roots may remain much too dry. To avoid this difficulty, poke holes in the soil and root mass using an ice pick or a wooden skewer to create spaces through which water can flow and then percolate into surrounding soil. You should also make plans to repot the plant, since this problem is often a symptom that more root space and a fresh supply of potting soil are needed.
Water will percolate more easily to a rootbound plant’s interior roots if you make small holes in the soil with a skewer or ice pick.
Although time consuming, bottom watering plants is often the best way to be certain that the lowest half of the root ball receives adequate moisture.
Another potential problem with top watering are water spots that form on plant leaves, which is a common issue with African violets, gloxinias, and other plants that have downy leaf surfaces. When any of these top-watering complications are present, water plants from the bottom. To do this, pour water into a tray or saucer, set the plant in it, and allow the plant to drink its fill for up to 30 minutes before emptying out any excess water. The biggest risk with bottom watering is waterlogging of roots, which is seldom a problem in small containers but may be if the pot is very large and made of plastic or another material that holds water well. Never leave a pot sitting in standing water for more than 30 minutes.
Most plants flourish when they are watered both ways — most often from the top, but occasionally from the bottom. Top watering is easy and practical, and leaf spotting can be minimized by watering in the morning and not soaking the leaves. Occasionally, do go to the trouble of bottom watering your plants. Bottom watering every month or so is an excellent way to avoid the formation of dry pockets in the container, a common problem with plants that are infrequently repotted.
Best water for plants. One of the facts of modern life is that we often don’t know what’s in our water. And some of the things we do know about, such as chlorine, are abhorred by plants. Confined to pots, indoor plants have no way to escape tainted water, so it’s crucial to give them water that’s at least as good as the water you like to drink. If you filter your drinking water, filter the water you give your plants too. If you suspect that your tap water contains too much chlorine for plants, allow the water to sit out overnight, which gives chlorine and other chemicals time to escape as gas. If you make a habit of refilling the containers you use to water your plants each time you finish watering chores, gases will slowly escape and the water will be ready to use by the time your plants need watering again.
Some people like to collect rainwater for their plants, an ancient ritual worth repeating whenever it’s convenient. Or you can use melted snow, which often contains traces of beneficial micronutrients.
Most plants prefer “soft” water to “hard” water. Soft water contains very low amounts of calcium and magnesium salts, while hard water, which often flows through deposits of mineral-rich rock, contains high amounts of these elements. Many people who have very hard water utilize water softeners, which remove these mineral salts through filtration, magnetization, or a combination of processes. Water softened in these ways still contains high levels of salt, which leads to problems when it is used to water plants. In place of softened water, use water that is naturally soft, such as rainwater or bottled distilled water for your houseplants.
Regardless of its source, make sure water is at room temperature when you give it to your plants. Giving cold water to tropical plants chills their roots, which can cause them to rot.
Rehydrating parched plants. If a plant dries out so severely that it collapses, promptly place it in a pail or sink of lukewarm water. It may be so dry that it floats! Use a large spoon or cup to ladle water into the top of the container, and then allow the plant to soak for about 30 minutes. Remove the plant and place it on a rack (such as a dish rack) until all excess water drains away and the base of the container no longer drips. Wait until the next day to decide if any leaves need to be trimmed off. Most plants recover well from drying out for short periods of time. However, repeated trauma can cause stems and leaves to die.
This is also a good procedure to try with plants that seem to stay dry even though you water them regularly. Sometimes the middle of a container dries out so much that water applied to the surface runs down the inside of the pot and out through the drainage holes before the roots have a chance to drink their fill. Rehydration can help, but you should also make plans to repot the plant.
Rescuing waterlogged plants. When plant roots sit in excess water too long, they start to rot. As the roots deteriorate, they cannot take up water, so the plant wilts. What seems like the thing to do — providing more water — can actually make things worse! If the container feels heavy yet the plant droops, you probably have a waterlogging crisis. To save the plant, place several thicknesses of newspaper in a pan or basin, lay the pot on its side, and slide out the root ball. Allow the root ball to dry on the newspapers overnight. Use clean sharp scissors to trim off any dark-colored or slimy roots before repotting the plant in a clean container with fresh potting soil. Adding small stones or pieces of a broken clay flowerpot — or even broken china — to the bottom of containers helps prevent this problem.
Rescue a waterlogged plant by slipping it out of its pot and laying the root ball on a layer of newspapers to dry overnight.
Indeed, overwatering is the leading cause of houseplant death. When you’re getting to know a new plant, it is better to err on the dry side than to drown its roots with too much water. In addition, be careful in the autumn. The reason? New growth slows as days become shorter, so plants need less water. And when plants are moved indoors after spending the summer outside, the absence of wind, combined with radically reduced light levels, further limits their need for water. Indoor humidity levels are often moderate in fall, too. When indoor humidity levels drop as the winter heating season begins, you can carefully increase watering until plants appear content.
Just as plant leaves make physical changes to adapt to increasing or decreasing levels of light, stems alter their structure to better cope with movement, which typically comes from wind. As long as plants are kept indoors, they encounter very little moving air. Their stems do not need to be tough, and so they often are comprised of cells arranged in straight patterns. In comparison, plants that are exposed to moving air respond by arranging their stem cells in more twisted patterns, which makes them less prone to bruising and breakage.
The transition from tender stems to tougher, wind-resistant stems takes time, so you should acclimate plants to wind that are being moved outdoors the same way you acclimate them to increasing light. Frequently these two goals can be accomplished together. Begin by placing plants in a shady spot that is protected from strong wind and sun, and gradually move them to a more open environment, over a period of 1 to 2 weeks.
Even properly acclimated houseplants may suffer wind damage when exposed to high winds outdoors. When very blustery weather is predicted, move houseplants to a protected spot, such as against the outer walls of your house, or simply bring them indoors until calm weather returns. In addition to twisting or breaking stems and leaves, wind can easily topple plants, which can lead to devastating damage.
You also can condition your plants indoors by running a gentle fan, which will cause enough air movement to trigger a response from the plants’ stems. In winter, you can keep your plants physically fit by talking to them as you water and groom them. The gentle puffs of air from your breath causes slight air movement, too.
Beautiful form, flawless texture, and a well-chosen container combine to make a mounding philodendron glow with satisfaction.
