One of the most common questions from new gardeners is, “What is the difference between a perennial and an annual?” So let’s define the difference immediately. An annual is a plant that grows, flowers, sets seed, and dies in one year. Sweet peas are annuals, as are zinnias, cosmos, and sunflowers.
A perennial is a plant that lives for at least three years in the garden. Many perennials are herbaceous—they die back to the ground in winter, leaving not a trace of their existence. Other perennials leave behind a rosette of leaves close to the ground, in anticipation of the next growing season. And a few perennials flower during the winter.
Some plants that we treat as annuals, such as petunias, have been bred from plants that are perennials, or perhaps even shrubs, in their native environment—usually one much warmer year-round than our Pacific Northwest. So is a petunia an annual? The answer begins to get a little fuzzy, and not to beginning gardeners alone. It is usually enough to know that in our climate we must treat it as an annual because of our growing conditions.
lily-of-the-valley (Convallaria majalis)
Between annuals and perennials are biennials. These are plants that live two years. The first year they grow, and the second year they flower, set seed, and die. Biennials are also a cloudy issue to gardeners. Foxgloves, some verbascum, and parsley are biennials, but gardeners know that those plants may not necessarily die the second year. And so now we hedge our bets by calling verbascum a “short-lived perennial,” which could mean that it lives two, three, or more years. But when it does die early, you can’t complain, because you were warned.
And then there are shrubby perennials and perennial-like shrubs. Shrubs have persistent woody stems aboveground. Garden penstemon have persistent, somewhat woody stems aboveground, but are considered perennials, not shrubs. Lavender’s woody branches are a giveaway to its classification—it’s a shrub, but because it’s small and flowers profusely, you may find them in the perennial section of the nursery. Plants such as lavender and sun roses (Helianthemum) are often called subshrubs.
Definitions set forth limits and boundaries, but it seems that definitions, like rules, are made to be broken—or at least stretched a bit. That’s why what you read in a book or magazine seems to run contrary to the basic definition of “perennial.” Bulbs, too, are often separated from a list of perennials, because their underground storage systems are actually modified leaf buds and not the fibrous roots we see when we dig up a plant such as a daisy.
While this book sticks with the definition of perennial as a plant that lives for at least three years, it seems natural to include a few plants that extend the horticultural definition yet fit so easily into a garden. And so this book includes a couple of bulbs (such as Allium) and biennials (such as common foxgloves, Digitalis purpurea), the occasional fern, and a well-placed grass or two.
There’s no denying that most of us fall in love with a plant, buy it, and then try to find a place for it in our gardens. Although we never actually outgrow this practice (and why should we?), eventually we begin to look at choosing plants by matching their characteristics to our garden.
It’s fortunate that most of our gardens include so many different microclimates and soil conditions that we can find a place for a broad range of plants. The rest of the world may believe that the Pacific Northwest is always gray and rainy, that we are the world’s largest shade garden, but we know better. We do have a summer, which is dry, and we can grow more than just woodland plants. The contrasts can be dramatic: The sun’s effect is accentuated up against a south-facing concrete wall, while the north side of a building can be in deep shade for much of the year.
For gardeners, a plant name consists of the binomial (the two-word scientific name) for the species, such as Campanula persicifolia for peach-leaved bellflower. The two italicized words together are the species, similar to your whole name including your first and last name. The first word is the genus, a large collection of plants; together with the second word, it makes up the species. There may be many kinds of sea holly (Eryngium), but only one yucca-leaved sea holly (Eryngium yucca-folium). Often, gardeners use the comman name for a plant—evening primrose for Oenothera—and sometimes the most common name is the same as the botanical name (Clematis). Here, you will find it both ways.
Some plants are classified as a subset of the species, because they have noticeably different characteristics. These plants have three words in their name, separated by “subsp.” for “subspecies” or “var.” for “variety.” Nursery tags may or may not include these designations.
The word “cultivar” is a combination of the words “cultivated variety.” A cultivar has been bred on purpose or selected from a group of seedlings or was found as a genetic mutation in nature. Sometimes the characteristic for which a cultivar was chosen and named comes true from seed, but most often these plants need to be asexually propagated—by division, tissue culture, or root or stem cuttings (see Chapter Three). The cultivar is written in single quotation marks, such as Heuchera ‘Green Spice.’
Although a plant’s scientific name is governed by strict rules, the cultivar name is up to the person doing the naming. Cultivars are often named for a person (‘Ann Folkard’), a place (‘Langtrees’), or the cultivar’s most noticeable characteristic (‘Orange Flame’). You may see the same cultivar name for entirely different plants: there is a Brunnera ‘Langtrees’ and a Dicentra ‘Langtrees’. Sometimes namers get downright poetic (‘Sops in Wine’). Guidelines say that cultivar names should not sound like Latin, so they aren’t confused with the binomial, but this rule hasn’t always been in effect; so you’ll see many names in single quotation marks, such as ‘Roseum’ or ‘Plenum.’
In catalogs and on plant tags, plant names often get mixed up, changed, misspelled, confused, and misapplied. Sometimes one or two of the words are left out. It’s like playing telephone: What was whispered in the first person’s ear (“play the record loud”) mutates almost beyond recognition by the time it gets to the last person (“buy stock now”). In this book, every effort has been made to list the correct binomial and cultivar of these perennials, but that is not to say that you won’t find them in a different form when you get to the nursery.
Where a plant has been reclassified (that is, taxonomists have realized that it was put into the wrong group), you’ll find the alternate plant name in parentheses with the abbreviation “syn.,” meaning this is a synonym. At the nursery, you may find either name.
umbrella plant (Darmera peltata)
Combine those varying light characteristics with the wide range of soil types, and we can grow just about anything we want—even within one garden. Even a suburban-size lot can include patches of heavy clay and gravelly loam. Hot and sunny with sandy soil? How about a stand of the architecturally cool Euphorbia characias? Heavy soil in the shade? Brighten it up with golden creeping jenny (Lysimachia nummularia ‘Aurea’).
A garden should be a symphony of movements that lasts all year. Sometimes that means choosing plants that have more than one ornamental characteristic. At other times it means choosing a variety of plants that each have but one moment of glory, but at different times. This creates a succession of interest in flowers and foliage.
In the great gardens of England, the long, deep herbaceous borders may lie dormant in winter, looking like a barren wasteland. That isn’t a concern, however, because the borders are often discreetly hidden from the house by yew hedges and old brick walls; those structures take over when there are no flowers. Out of sight, out of mind. But at Great Dixter in East Sussex, for example, where the long border previously was known mostly for its midsummer glory, pains have been taken to extend the border’s show to begin in early spring and last well into fall.
In the mild maritime Pacific Northwest, it isn’t difficult to find plants and combinations that carry through winter. The sections below provide a snapshot of one section of a garden; in a whole garden, the effect can be multiplied or mixed. (For more on designing with perennials, see Chapter Two.)
Let’s take one small piece of ground and see how it can be planted with four perennials for year-round ornamental characteristics.
• Bergenia ‘Winterglut’
• Penstemon ‘Garnet’
• Carex testacea
• Helenium ‘Moerheim Beauty’
Three of these four plants have showy flowers. The Bergenia has deep red stems topped with deep pink flowers in late winter. Penstemon flowers in June and again in September if cut back after its first flowering. Helen’s flower (Helenium) begins blooming in late July and can be cut back for more flowers in autumn.
But what this combination has is staying power. Whether the plants are in or out of bloom, there is always something to see. Of the three, Helenium is the only herbaceous plant. The deep reddish tones of the Bergenia and the orange grass Carex testacea stand out in the winter landscape, and the green stems of the penstemon (before being cut back themselves in late winter) add a bright touch.
Now let’s take that same small piece of ground and look at planting for a succession of blooms.
• Pulmonaria ‘Roy Davidson’
• Omphalodes ‘Starry Eyes’
• Hosta ‘Blue Cadet’
• Cyclamen hederifolium
• Aster divaricatus
• Helleborus × hybridus—a dark one and a white one
This collection of shade plants lends a cheery note throughout the year. In light shade, lungworts (Pulmonaria), also known as soldiers-and-sailors for their two-tone blooms, start flowering in early spring. The flowers open pink and turn blue (although there are pure white cultivars, such as ‘Sissinghurst White’); they are set off by green leaves with silver spots. Following close on the lungwort’s heels are the intense blue flowers of Omphalodes, a low-growing charmer.
The blue-green foliage of the small Hosta ‘Blue Cadet’ has already unfurled and carries interest through the summer when its spikes of lavender flowers appear. In late summer, the bright pink flowers of the hardy cyclamen appear, followed by its marbled foliage, which stays through winter. Also in late summer, the wood aster (Aster divaricatus) blooms in a mass of tiny white starry daisies. And by late December, the hellebores are sending stems of flowers up.
Understanding Hardiness Zones
The U.S. Department of Agriculture (USDA) has established eleven hardiness zones that are based on the average minimum winter temperature. The USDA hardiness zones are often listed inclusively (zones 3–8), to show not only the minimum temperature that the plant will survive, but also to suggest the plant’s upper temperature limit. Much of the Pacific Northwest is zone 7 or 8.
For many of the plants listed in Chapter Four, you’ll find that the upper zone limit is listed in national reference books as zone 7. That would certainly cut out a great deal of our region. The national guides do this because USDA zone 8 also includes much of the South, where hot, humid summers are the death of many delicate perennials. What we share with the South is an average minimum winter temperature—but our summers are a world apart. And apparently we are the only ones who know this.
toadflax (Linaria purpurea ‘Canon Went’)
Doing some research before you buy a plant goes a long way toward arranging plants in your garden for maximum effect with minimum problems. But often a nursery visit results in on-the-spot purchases, so you also need to be able to read and interpret the plant tag. These tags can provide you with loads of information about the plant, including its name (botanical and common—see Understanding Plant Names, this page), hardiness zones (see sidebar, this page), most suitable aspect (see Planting Perennials, this page), bloom time, and ultimate size.
What plant tags don’t tell you is exactly how the plant will grow in your garden. Your garden is different from everyone else’s, and the effects of every condition whether large or small—from how much sun and water to what kind of micronutrients are present in the soil—can change the way a plant looks. The flower color may be slightly different, the plant may be more hearty (and hardy), or it may languish. That is something you learn in time, and it makes your garden a kind of scientific experimental ground from which you and others can gather anecdotal information. There are no control groups; you are not able to know the exact conditions under which a plant grows in someone else’s garden.
That’s why there is such lively discussion among gardeners: Our gardens provide us with a never-ending source of entertaining anecdotes. “My Eupatorium gets taller than that.” “My hosta ‘June’ grows in full sun and looks great; I don’t see why people say they need shade.” “I tried growing rocket and it died.” “I planted rocket and now it has spread all over my garden.”
Just as a sign that says “Antiques and Collectibles” can cause some people to step on the brakes, the word “nursery” on a sign gives gardeners pause. Why not stop and take a look? It’s like window-shopping at Nordstrom: We don’t have to buy anything; we just want to see what they have. And maybe have lunch or a coffee. And maybe get that one gorgeous blue poppy that we haven’t seen anywhere else.
A gardener’s favorite local nursery is the source of most of the plants in that person’s garden, but it doesn’t stop there. The world is full of purveyors of plants for our shopping pleasure.
Don’t you just hate it when you read about a really cool plant, and then you can’t find it? The plant may be rare, or it may be so popular it’s difficult to track down, but either way, our resources for finding plants are growing by leaps and bounds, and you need to investigate all avenues before you can truly say that you can’t find a plant. And then, of course, just like that silly butterfly of happiness, the minute you stop looking and are still, it will come to you. But before you succumb to sugary metaphors, try these strategies.
• Don’t just scan the shelves at your local nursery and then give up when you don’t see something on your list. Ask. Nurseries have a regular list of companies from which they buy, and they continually receive plant orders from growers and wholesalers during spring, and regularly at other times of the year. Maybe the plant you seek is on next week’s list. If it isn’t, find out if it can be special-ordered. If not, try at another nursery, which may buy from other places.
• Perhaps this is the kind of plant that won’t show up at a regular, full-service nursery. Then try a specialty nursery or mail-order catalog. A Web search may turn up likely sources for your plant.
• Go to plant sales. Every year, especially in spring, dozens of organizations, such as the Washington Park Arboretum Foundation and the Hardy Plant Society of Oregon, put on plant sales as fund-raisers. Those same specialty nurseries you are trying to track down may very well be in attendance there. It’s like having the results of your Google search in the flesh. And most plant sales also have a donor table, where generous members share treasures out of their own gardens.
• Visit some fabulous gardens that are open to the public. Often those gardens sell plants that have been propagated from seeds or cuttings of plants in the garden. Great plants, great deals.
• At the very least, make many other people aware of your search.
• If you haven’t found the plant after all your efforts, it may be time to take the butterfly of happiness approach.
In a perfect world, we’d plan the garden and then buy the plants. But we know that often doesn’t happen, and even if you have planned and planted, there’s all that editing to do as the years go by. Even in an imperfect world, these tips on timing your purchase will help you end up with an almost-perfect garden—that is, one that makes you happy:
• When you are buying at the nursery, consider the time of year and read the tag carefully for the growing information you need. Nurseries tend to carry perennials that are in or almost in bloom. That means that you won’t find many asters on the nursery shelf in April, but by August the place is sure to be awash in them.
• Buying herbaceous plants in winter is an exercise in faith—sometimes you get nothing but a pot and a promise. In winter, you may find perennials for sale in bags of damp wood shavings. The bag contains the roots and crown (the part just at or slightly above or below the soil line). When kept cool, in the dark, and moist (but with a little air circulation), the roots will last for several weeks like this. But you don’t know how long they have already been in the bag, so your first task is to pot them up or plant them out.
• It used to be that in spring and early summer, everything on the nursery table looked good, but now it seems that plants arrive from the growers just as fresh in September as they do in March. We fall for their beauty in spring, but we look for good deals beginning in midsummer, when nurseries often start putting perennials on sale.
• Mail-order catalogs offer a year-round selection of plants (unless they are sold out). Buying from a catalog also means that you have more time to peruse. Catalog descriptions are as good as a plant tag—sometimes even better, because they often include personal comments from the writer. You don’t always get photos, but then, that’s what this book is for.
Japanese painted fern (Athyrium niponicum var. pictum)
Here are some tips to consider when buying perennials for your garden:
• You would think that perennials in 1-gallon containers are better than plants in smaller pots, because the gallon plants are big enough already to make a splash in your garden—no waiting necessary. But consider this: You can buy more plants if you choose those in 4-inch pots because they cost less, and sometimes plants in 1-gallon pots are just 4-inchers that have outgrown their containers and have been potted up. In other words, you may be paying for more soil, but not necessarily more plant.
• Smaller plants are easier to establish in the garden. They take less water and recover quicker if they are potbound and you must rip up the root ball.
• Buy a healthy plant. It’s possible to rescue plants that are potbound and wilted, but be aware that it will take extra effort. The healthiest plants will have mostly undamaged foliage (it can be a rough life on the nursery shelf, and a tattered leaf or two shouldn’t cause concern). It won’t have lots of brown roots coming out of the bottom of the pot. Check for lurkers in the soil surface: little weeds, moss, and liverworts looking for a free ride home with you.
A common complaint of gardeners is that their new plant didn’t bloom when they planted it, or perhaps the floral show was less impressive than they expected. But to the plant, flowers have more than a decorative purpose; they are a means (pollination) to an end (reproduction). And flowers expend a lot of the plant’s energy—energy it may not have when it is first planted. The old adage is annoying and cutesy but true: First they sleep, then they creep, then they leap. In other words, don’t expect much of a show from a first-year perennial.
Planting Perennials Under Trees
Planting a perennial garden under existing trees is not impossible, but it certainly is not the easiest thing to do. Here are a few suggestions:
1. Buy small plants so that you won’t have to dig a big hole in soil that will be hard and full of roots.
2. Established trees don’t need irrigation except during times of unusual weather patterns (a dry spring followed by our typically dry Northwest summer), so choose perennials that prefer dry shade and you won’t have to continue watering past the establishment phase—through the plant’s first summer.
3. Mulch well, but don’t pile it up around the trunk of the tree or the flare (the base of the trunk where it spreads out at soil line); keep the mulch several inches away.
purple coneflower (Echinacea purpurea)
The best time to plant perennials is when you have the time to do it. That said, we usually think of spring as planting time. The earth is awakening, our body clocks are kicking into high gear, the sun is shining longer, and plants are growing.
In spring, a plant’s growth is upward and outward. A healthy containerized plant will be ready to take on the new year’s growth, and its root system, although not well-established, will be up for the challenge of growing new leaves. The new leaves in turn make food through photosynthesis; the food is sent down to the roots. The first year’s floral show may not be as extravagant as those in later years, but if the plant is healthy, we don’t mind. It is important to remember to water spring-planted perennials during their first summer; their root system isn’t extensive enough to compensate for a lack of regular moisture.
A hot day in July may not be the best time to plant, but sometimes it’s all we’ve got. Planting perennials during a typically dry Pacific Northwest summer means taking a little more care about how you do it:
1. Water the container plant the day before you plant it.
2. Avoid planting in powdery-dry soil; water that, too, the day before, if necessary.
3. After planting, be sure to water the plant well (see How Do I Plant It, this page).
4. Mulch the plant with well-composted material. Don’t mulch dry soil, because it will take longer to get moisture through to the soil. Mulch is the great moderator; it slows the flow of water into the ground. That means that in winter, mulched soil doesn’t get as soggy as fast as unmulched ground, but it also means that bone-dry soil that gets mulched won’t take up as much water as those newly planted roots will need.
Fall is a fabulous planting time: The air gets cooler, which is less stressful on plants, yet the ground is still a warm, cozy, inviting environment for roots. Fall is also an underappreciated planting time, because there are fewer plants in bloom to dazzle us at the nurseries. Plant in fall, and you will have to water less because our rainy season begins in October.
The terms “sun,” “shade,” and “part shade” are used to guide you in placing perennials in the garden. “Sun” means the plant needs six hours or more of sunshine a day from spring into fall. “Shade” means the plant needs six hours a day of shade from trees and shrubs. “Part shade” means the plant needs a half day of sun—how’s that for confusing? There are extremes, exceptions, and extenuating circumstances, of course. Usually, plants that prefer part shade grow best in morning sun, with shade from the afternoon’s hotter rays. There’s a difference in shade from trees (dappled) and shade from a building (complete). Full sun in the middle of a lawn is cooler than full sun up against a south-facing wall. Fortunately, there are plants that take the extremes, and this is noted in that plant’s listing in Chapter Four.
It’s tempting to think we can get away with planting a perennial in a spot that does not meet its cultural needs. We’re tempted even further if we have ever gotten away with the practice. “But I have an Aster ‘Mönch’ that does just fine in shade.”
Planting Perennials in Pots
There are a few differences between planting perennials in containers and planting them in the ground:
1. If you plant a container with several plants, be sure it’s wide enough.
2. The depth of the container is up to you: Perennials can survive in as little as 8 inches of soil, but you’ll be standing over them with the hose in the summer, watering every day. On the other hand, if you choose a pot that stands 24 inches high but want to put small plants in, you’ll be wasting a lot of potting soil if you fill the entire pot and the plant only wants 8 inches of soil. You can use a piece of fine hardware cloth (rugged galvanized screening) cut to fit snugly into the pot as the “bottom.” This will provide that all-important drainage yet keep the soil in the top 10 or 12 inches of the pot, so you won’t be washing away the plant’s environment.
3. When you plant, set the plants so that you fill the pot up to within an inch from the rim. That way, when you water the container, the water won’t all run out over the sides.
4. Pots dry out faster than the ground, so your main concern with containers will be summer watering. Terra-cotta dries out quickly in warm weather; check these pots daily. Glazed or water-sealed terra-cotta retains water longer. Faux terra-cotta pots are looking more stylish all the time and they are a cinch to use: They dry out more slowly and are lightweight.
5. In winter, your main concern will be keeping the pots from being waterlogged. Pot feet help keep drainage working. Drawing pots up under the eaves of the house helps, too. If there is the potential for below-freezing temperatures—especially days filled with freezing, dry, desiccating winds—then wrap the pots with layers of newspaper or bubble wrap or take them into an unheated garage until the weather has settled down.
6. The soil in the pot will decrease as time goes on, so perennials that you keep permanently in the container will benefit from having fresh soil added. Or take the plants out and refresh the entire container.
“I never water my Lobelia cardinalis, and it looks great.” It’s true that some plants have a higher tolerance for inappropriate conditions than we may realize. It may also be that if you meet one requirement that is more important than another, you can keep a plant happy and growing. For example, some shade plants, such as astilbe, will tolerate a fair amount of sun, if provided with regular (some might say, copious) amounts of water.
Toying with a cultural requirement isn’t exactly playing with fire, but then, you won’t get a lot of sympathy when you whine that your Brunnera ‘Jack Frost’ withered when you planted it in your full-sun rockery. Perhaps it would be better to keep ‘Jack Frost’ in a pot until you’ve found a nice shady spot. Maybe you could plant up a nice container that would work well in a shady entryway. Combine the herbaceous Brunnera with an evergreen such as one of the hellebores (Helleborus foetidus has fingerlike leaflets that would look good in contrast to the Brunnera’s wide, solid foliage). Stick a few hardy cyclamen in for a shot of pink.
Generally, the planting instruction for perennials is simple: Just stick it in the ground.
But then we look at how the plant grows in the pot and wonder if it’s OK to cover up any stems with soil. Then we take it out of the pot and see that its root system is one solid chunk of brown roots circling the inside of the pot, and we wonder: Should I do something about that? What about fertilizer and mulch in the planting hole? See, there’s more to it than you thought.
1. Because you should plant in moist ground—not wet and not powdery dry—you may need to water the ground the night before if the weather has been dry.
2. When you plant an entirely new garden, you can dig one giant hole for all the plants and prepare the ground beforehand. When you are adding a plant or two here and there in the garden, dig smaller holes for specific plant sizes. If you are planting a perennial from a 4-inch container, use a sturdy trowel to dig a hole; if you are planting from a 1-gallon pot, the best tool for digging among existing plants is called a poachers or planters spade. It has a long, narrow scoop or blade (the part you stick in the ground) and is less likely to damage neighboring plants. Use one with a short, D-shaped handle, and you won’t bump the handle end into a nearby fence or tree. Dig a hole that’s wider and a little deeper than the pot. This loosens up the soil and gives the expanding roots an easier time of it. Mound up the soil in the hole a little bit, so that you don’t bury the crown of the plant.
3. It is important to examine the condition of the plant’s roots when it comes out of the pot. A potbound plant will have little soil left in the container; instead, the roots will have filled up the space. The brown roots you see circling around are not doing the plant much good. The white, healthy roots grow tiny root hairs that pull in water and minerals for the plant. Use a hand cultivar to comb out the roots, loosening the solid mass. You can trim off excess brown roots (several inches’ worth is OK) with scissors or hand-pruners. The roots of a plant in a small pot can be loosened by hand.
4. Place the plant in the hole so that its crown ends up just an inch or two above soil level.
5. Fill the hole around the plant with soil and water it well, adding more soil where you see pockets of soil sink. With trees and shrubs, it’s important to backfill with the same soil that you dug out of the hole, but with perennials the rule is relaxed somewhat. You can backfill with soil mixed with compost if you want, but you’re making more work for yourself. Instead, see the next step.
6. Mulch after planting. Apply a layer of well-composted material such as composted yard waste or washed dairy manure. “But wait,” you say, “I have heavy clay soil and I wanted to make it better by adding compost to the hole.” Fine—mix and backfill, mix and backfill. But it’s easier to wait until you have finished planting and add the mulch; it does the same job. Or, rather, the little fauna of the soil do the job for you. As the compost breaks down, it is taken into the soil and the soil texture is improved. Let those worms do their work!
7. Gardeners can’t keep their hands off the fertilizer bag. In general, the garden can get all the nutrients it needs from the soil and—here it comes again—that layer of well-composted organic material, the mulch. However, some needy plants—roses, for example—do need to be fertilized after planting, and lilies and delphiniums perform better when given extra nutrients.
globe thistle (Echinops ritro)
