See Narcissus
Dahlia. Summer- and fall-blooming tender perennials.
Description: Dahlia flowers range in size from 1 inch to well over 1 foot wide and are available in all colors except blue and green, in solids and mixes, often brushed or speckled. They also come in many forms, so check the bloom type when you order plants online or through catalogs so you won’t be surprised at bloom time. Single flowers have one row of petals around a yellow center. Semidoubles have a few rows of petals around the center. The anemone form resembles a single but also has a tuft of petals around the center; collarettes have a collar of petals instead of a tuft. Cactus dahlias are double flowers with tubular, almost pointy petals. Formal decoratives are double flowers with broad petals in a neat pattern, while informal decoratives are doubles that look less neat and often have twisted petals. Ball dahlias have double, ball-shaped flowers with cupped petals turned toward the center; pompons are like balls, but are less than 2 inches wide.
Most dahlias grow 2 to 6 feet tall and may spread almost as wide, bearing thick bamboolike stems and lush green or dark purple-red foliage resembling giant celery leaves. (The famous cultivar ‘Bishop of Llandaff’ bears scarlet semidouble blooms above foliage so dark it’s almost black.) The leaves may be only 3 to 4 inches long, or they may exceed 1½ feet. Dahlias are hardy in Zones 8–11 if soil is well drained and not allowed to freeze; otherwise, lift them for winter.
How to grow: You can start dahlias indoors, treating them like caladiums (see the Caladium entry), or plant them directly into the open ground after it has warmed up. Either way, plant them outdoors after all danger of frost is past, in full sun and deep, fertile, moist but well-drained soil enriched with plenty of organic matter. Whether plants are already in leaf or not yet growing, set the roots horizontally 3 to 6 inches below the soil surface. If already started, carefully break off the lowest leaves to encourage additional roots to form. Don’t cover unsprouted tuberous roots completely at planting time—gradually fill in the holes as the plants grow.
After setting out each plant, immediately drive a sturdy stake 6 inches from the growing point, especially for tall cultivars. Don’t wait until the plants are up and growing, or you may damage the tuberous roots. Mulch thickly with pine needles, straw, or compost after plants are at least 6 inches tall and the soil is warm. Water often, and fertilize liberally throughout summer with fish emulsion, liquid seaweed, compost tea, bonemeal, or other fertilizers not excessively high in nitrogen. See the Compost entry for instructions for making compost tea.
When plants are about 6 to 10 inches tall, pinch out the center to promote branching and more flowers. You can pinch them again after they put out another 6 inches of growth. Tie the shoots to the stake as they grow long enough. When the flower buds reach the size of a pea, remove the side buds to allow the center one to grow as large as possible for its type, or leave the side buds on for more but smaller flowers.
Handpick slugs and snails when the plants are small, and apply soap sprays to control spider mites in summer. Corn stem borers may attack dahlias, so be on the lookout for wilting shoots and cut them back until you find the borer. Cucumber beetles and grasshoppers relish the flowers; handpick these pests daily. For more cucumber beetle control options, see the Cucumber entry. To help keep viruses from spreading, immediately destroy any stunted plants or those with yellow-streaked, twisted leaves.
After frost blackens the plants, cut them back to a few inches above ground level, lift the clumps from the ground, and store them on their sides while waiting for the soil on the tubers to dry. Label them with their cultivar names, using an indelible pen or attachable tag. Store as entire clumps with the soil remaining on them, or remove the soil and store the root clumps in barely moist peat or vermiculite in a cool (45° to 50°F) spot, sprinkling a little water on the peat or vermiculite to plump up withered tuberous roots. To multiply your collection, cut up the clumps in spring, making sure each piece has a small pinkish “eye” attached to it.
Landscape uses: Many of the shorter and medium-height dahlias make excellent additions to the late-summer and fall border. Taller dahlias can temporarily screen out an unpleasant view. They’re also colorful in front of a tall hedge (leave a few feet between the hedge and the dahlias). Add dahlias to your cut flower garden for beautiful late-season bouquets.
See Chrysanthemum
Cinquefoil. Spring- and summer-blooming deciduous shrubs.
Description: Dasiphora fruticosa (aka Potentilla fruticosa), shrubby cinquefoil, is an exceptionally hardy shrub. It has a low, twiggy, rounded form, growing to 2 to 4 feet tall and wide. The compound leaves are a soft gray-green. Lemon yellow, 1-inch flowers cover the plant in late spring, followed by sporadic bloom through summer and into fall. Zones 2–7.
How to grow: Cinquefoil does best with full sun in well-drained soil. Once established, it needs little supplemental watering. Prune in late winter before growth begins.
Landscape uses: Because of its compact size, cinquefoil makes a good foundation plant. It is also effective as a specimen, in mixed borders, or in a massed planting.
See Hemerocallis
Delphinium, larkspur. Summer- and repeat-blooming perennials.
Description: Delphinium elatum hybrids, hybrid delphiniums, bear 2- to 3-inch single, starlike or semidouble, rounded flowers, in white, pink, lavender, blue, purple, and combinations on dense spikes that rise 4 to 6 feet above maplelike leaves on long stems. Zones 3–7.
D. × belladonna, belladonna delphiniums, have 1½- to 2-inch single blooms in white and blue, borne loosely on numerous spikes above smaller, deeply lobed leaves; plants grow 3 to 4 feet. Zones 3–7.
How to grow: Set out plants or rooted cuttings in spring; sow seeds indoors in winter for summer bloom or in midsummer for bloom next year. Plant in a sunny site in fertile, humus-rich, moist but well-drained soil. Delphiniums prefer regions with cool summers; if you have hot summers, try them in a partly shady, moist area. While good air circulation is desirable, avoid sites where winds will batter the tall flowerstalks.
Feed and water hybrid delphinium cultivars regularly. They’ll also need staking to support their towering flower spikes. Deadhead, water, and fertilize all cultivars immediately after flowering to promote rebloom. Wide spacing increases air circulation, reducing disease problems. Hose off spider mites regularly if they appear. Divide and replant overgrown clumps in spring.
Landscape uses: Use tall cultivars as exclamation points alone or in groups at the back of borders and against buildings, fences, walls, and hedges—anywhere you’d like a strong vertical accent. Mass shorter cultivars in borders or a cutting garden. Delphiniums are ideal for cottage gardens.
Pinks, carnations. Spring- and summer-blooming perennials.
Description: Cheerful pinks offer a variety of single to double flowers in shades of white, pink, and red. The petals are fringed and often banded with color. Flowers may be richly clove scented and are borne on thin stems above tufted or mat-like grassy leaves.
Dianthus × allwoodii, Allwood pinks, produce mostly double 1- to 2-inch blooms in summer, 12 to 15 inches above attractive gray-green mounds of foliage. Zones 4–8.
D. deltoides, maiden pinks, bear masses of ¾-inch flowers 6 to 12 inches above spreading mats of leaves for several weeks in summer. Zones 3–9.
D. gratianopolitanus, cheddar pinks, bear ½- to ¾-inch flowers up to 1 foot above small mounds of narrow, gray-green leaves in spring and sporadically through the season. Zones 3–9.
D. caryophyllus, florist’s carnations, need greenhouse conditions and are not suitable for the garden.
How to grow: Plant or divide in spring or fall in a sunny spot with average to low fertility and well-drained, slightly alkaline soil. Although maiden pinks tolerate very light shade, anything less than full sun usually results in weak, floppy stems and dead central leaves. Maiden and cheddar pinks will rebloom if promptly deadheaded. To avoid crown rot disease, don’t plant pinks in poorly drained soil.
Landscape uses: Perfect for edgings and in rock and cottage gardens, pinks are also delightful in groups in the front of borders or filling gaps in stone paths. Grow maiden pinks as a groundcover; try the tiny ones in shallow pots. Cheddar pinks make great groundcovers, too. Allwood pinks make good cut flowers.
Diascia, twinspur. Summer- to fall-blooming annual or tender perennial.
Description: Charming relatives of snapdragons, diascias bear heart-shaped leaves and loose racemes of ¾-inch flowers in shades of pink. Each flower has two spurs in the back and five rounded lobes in front. The low-growing, 1-foot-tall plants have sprawling stems that spread to 2 feet.
How to grow: Diascias need full sun to light shade and rich, well-drained, evenly moist soil. Start seeds indoors 8 to 10 weeks before the last spring frost, sow seeds outdoors 2 weeks before the last frost, or purchase started plants. Pinch plants when they are 3 inches tall to encourage branching, and cut them back to 3 inches after the first flush of bloom to encourage repeat flowering. They may stop blooming during hot summer weather. Take cuttings in late summer or dig plants for overwintering indoors.
Landscape uses: Use diascias to add color to beds, borders, and rock gardens. They’re also a great choice for containers.
Bleeding heart. Spring- and recurrent-blooming perennials; wildflowers.
Description: Bleeding hearts bear clusters or sprays of heart-shaped flowers above mounded leaves.
Dicentra eximia, fringed bleeding heart, blooms in late spring and sporadically through the season, with clusters of narrow, ¾-inch pink flowers on 1- to 1½-foot slender stems. Its blue-green leaves are delicate and ferny, often with a grayish sheen. Zones 3–9.
D. spectabilis, old-fashioned bleeding heart, now listed by some sources as Lamprocapnos spectabilis, blooms in spring. It bears 1½-inch pink-and-white flowers that dangle in rows from gracefully curving stems up to 2 feet long, above a 2- to 3-foot mass of blue-green leaves. Some cultivars bear pure white flowers, and one, ‘Gold Heart’, has chartreuse-gold foliage and deep pink flowers. Zones 2–9.
How to grow: Set out bleeding hearts in early spring. Plant either pot-grown specimens or divisions, but handle them with care, since bleeding hearts have brittle roots that are easily damaged and generally resent disturbance. Grow them in partial shade and well-drained, humus-rich soil. Most reseed prolifically where conditions suit them. Water all bleeding hearts during drought. Old-fashioned bleeding heart tolerates full sun if given plenty of moisture during active growth. It dies back to the ground in summer or even sooner in hot, sunny spots (though in cool, shaded areas, the foliage may remain until early fall); remove the leaves when they start to turn brown and unsightly. Divide overgrown clumps when plants go dormant.
Landscape uses: Grow fringed bleeding hearts in woodland plantings, shady rock gardens and walls, and even in the shade of larger plants in sunny borders. Old-fashioned bleeding hearts are one of the best plants for spring borders and combine well with tulips. Grow old-fashioned bleeding hearts with hostas, ferns, and astilbes to fill in blank spots when the foliage dies in summer, or overplant carefully with annuals.
Foxglove. Summer-blooming perennials and late-spring- to early-summer-blooming biennials.
Description: Digitalis purpurea, common foxglove, is a biennial that carries long spikes of 2- to 3-inch, tubular, open-faced bells in shades of white, pink, and red-violet (usually spotted inside), on 4- to 5-foot upright, leafy plants. In the first year, young plants form a tight rosette of oblong leaves to 1 foot or more; the next spring and early summer, the bloom spikes emerge, set with progressively smaller leaves stopping just below the flowers. Zones 4–8.
Perennial D. grandiflora (also sold as D. ambigua), yellow foxglove, is similar to common foxglove, bearing spikes of 2-inch yellow flowers marked with brown inside on 2- to 3½-foot open clumps of dark green, narrower, more pointed leaves. Zones 3–8.
D. × mertonensis, strawberry foxglove, is a short-lived perennial that produces spikes of 2½-inch rosy pink blooms patterned with coppery lines on 3- to 4-foot oval-leaved plants. Zones 3–8.
How to grow: For biennial foxgloves, set out nursery-grown plants in late summer, or start from seeds sown in midsummer. Outdoors, sow in a protected spot away from strong sun and wind, scattering the seed into lightly raked open ground. Or start in flats, lightly pressing the fine seed into the growing medium. Foxgloves grow best in partial shade and average to fertile, moist but well-drained, humus-rich soil. They tolerate full sun farther north if kept moist. Water if the soil is dry, especially in spring. Keep stakes handy, particularly if the plants are growing in windy areas. After the ground freezes, place pine needles, straw, or other light mulch under the leafy crowns to help prevent root damage in winter.
After bloom, cut the flower stems off to encourage possible bloom the next year, or remove the entire plant. If you allow some plants to go to seed, foxgloves will self-sow readily and form impressive stands where conditions suit them.
Grow perennial foxgloves in similar conditions, dividing every 2 to 3 years in spring to keep them vigorous.
Landscape uses: The dramatic vertical spires of foxgloves add height and contrast to more rounded and spreading shapes in a border or cottage garden. Allow them to naturalize in lightly shady, moist woodland settings. Plant in the cutting garden for stunning cut flowers.
Division is a quick and reliable way to propagate many types of multistemmed plants with almost guaranteed success. Dividing—separating a plant into several smaller new plants—works well for increasing groundcovers, clump-forming perennials, bulbs, and tubers. You can divide ornamental grasses and suckering shrubs, as well as houseplants and herbs. Division is also an effective way to rejuvenate overcrowded clumps of perennials and other plants.
Season: The best time to divide garden plants is when they are dormant. In general, divide spring- and summer-blooming plants in fall, and fall-blooming plants in spring. If possible, divide houseplants in spring as new growth starts. Divide plants with tubers and tuberous roots, such as dahlias and tuberous begonias, before planting in spring.
Getting started: The key to division is starting with a vigorous parent plant. If the soil is dry, water the plant thoroughly the day before. Whenever possible, wait for cool, cloudy weather (or at least evening) to reduce moisture loss from the plant during the process.
Method: To divide a hardy plant, lift it from the soil with a fork or spade. Separate small clumps by pulling off the vigorous young plantlets; cut larger clumps apart with a knife or pry them apart with back-to-back forks. To divide heavy clumps such as ornamental grasses, cut them apart while they are still in the hole, then pull up the clump in pieces. Cut apart iris rhizomes with a knife. Discard the woody growth at the center of divided clumps. When dividing plants, make sure that each piece you remove has its own root system. Otherwise, new divisions won’t grow.
Lift clumps of hardy bulbs after the foliage yellows and dies down. Separate the bulbs and replant them at the proper depth and spacing. Divide tubers and tuberous roots in early spring. Cut dahlia crowns apart with a knife: Make sure each swollen root has at least one bud, located on the stems where the roots join the crown. Cut begonia and caladium tubers into two or three sections, each with a visible bud or sprout. Expose the cut areas to air for a day or two before planting.
Aftercare: Replant divisions as quickly as possible, to the same depth as the original plant, and water them thoroughly. Mulch fall divisions well to protect the developing roots from frost heaving.
Dividing herbaceous plants. Use a sharp spade to divide perennials or tough clumps of ornamental grasses. Try not to chop at the roots; make single, clean cuts whenever possible.
See Cornus
See Soil
If you’re not using drip irrigation in your garden, now’s the time to start. Drip irrigation is a highly efficient way to water, saving time and helping to conserve precious supplies of clean water. Studies show that well-designed drip systems use at least 30 percent, and in some cases 50 percent, less water than other methods of watering such as sprinkling.
A drip irrigation system delivers water directly to the root zone of a plant, where it seeps slowly into the soil one drop at a time. Almost no water is lost through surface runoff or evaporation, and soil particles have plenty of opportunity to absorb and hold water for plants. It also means very few nutrients leach down beyond the reach of plant roots. Furthermore, since drip irrigation delivers water directly to the plants you want to grow, less is wasted on weeds. The soil surface between the plants also remains drier, which discourages weed seeds from sprouting.
For busy gardeners, the main benefit of drip irrigation is the savings of both time and effort. Drip systems eliminate the need to drag around hoses and sprinklers. For systems that use a timer, gardeners need only spend a few seconds to turn the system on; the timer automatically turns it off.
Plants watered with drip systems grow more quickly and are more productive, because they have all the water they need and their growth isn’t slowed by water stress. (This is especially true when drip irrigation is used in conjunction with mulch.) Also, plants watered by drip irrigation don’t end up with wet foliage from a sprinkler spray, and that can help prevent some foliage diseases such as powdery mildew.
As wonderful as it is, drip irrigation won’t meet every watering need in your yard and garden. For smart tips on hand watering or using sprinklers, see the Watering entry.
The easiest way to experiment with drip irrigation is to buy a couple of soaker hoses. These hoses (some made from recycled tires) ooze water over their entire length. You simply position a soaker on the soil surface next to the plants you want to water, and then connect the open end of the hose to your garden hose and turn on the water supply. You can move the hose from one bed to another in your garden, or buy several and leave them in place. Soaker hoses can be used for short runs (100 to 200 feet) over flat surfaces. A soaker hose delivers water less precisely than a drip irrigation system but is still significantly more efficient than a sprinkler.
Soaker hoses are great for row crops such as carrots and beans, but for watering trees and shrubs or a series of containers, drip irrigation offers a more sophisticated and targeted way to water. Drip irrigation systems move water at low pressure through a series of tubes and other hardware and deliver it to precise locations and specific plants of the gardener’s choosing. Although each system is different, water generally flows out of your faucet through a timer (which is optional), a filter, a pressure regulator, and into a series of hoses or pipes that carry water to emitters, which are small devices that release water drop by drop to the plants. Some systems use drip tape—flattened plastic hoses with holes at regular intervals. A complex system may contain two or more individual lines as well as valves that allow for watering specific parts of the garden.
The first step in designing a drip irrigation system is deciding what you want the system to water. Is it only for your vegetable garden, or will you use drip irrigation for your entire landscape? Topography is also a consideration: If your garden is hilly, you’ll probably need to use emitters that compensate for pressure changes in the line.
Keep in mind that plants can become “addicted” to drip irrigation, because roots will concentrate in the area where the water is available. When designing a drip system to carry water along the rows of a vegetable garden or to the roots of a prized rhododendron, it’s important that the water be spread uniformly throughout the irrigated area so root growth will be uniform. For example, if you are irrigating larger plants such as trees and shrubs, place emitters on two or more sides of each plant to encourage roots to grow out in all directions rather than clustering on one side. For the same reason, it’s best to use your system to provide a long, slow watering. If you turn it on for frequent, short waterings, water won’t have a chance to spread far in the soil, and consequently the roots will form a tight, ball-like mass around the emitters.
You can design your own system, but most companies that sell drip irrigation equipment will design systems for you if provided with a scale drawing of your garden, information on what you’re growing, your soil type, and garden topography. Their design will come complete with a list of parts and spacing for emitters. Whatever method you choose, start by making a fairly accurate drawing of your garden to determine how many feet of tubing you’ll need.
If you’re designing your own system, consider asking a few gardening friends to adopt drip irrigation, too. That way you can split the cost of the system components, which have a lower base cost when you buy large quantities such as 500-foot-long rolls of drip tape or sets of 100 emitters.
Kits for beginners. A low-risk way to get started with drip irrigation is to buy a starter kit. Most companies that sell drip irrigation systems also offer kits for both small and large gardens, which come with the essential components necessary to set up the system. Keep in mind that kits often don’t include parts such as pressure regulators, timers, backflow preventers, and line filters. Be sure to buy a kit that can be expanded, so you can add to your system over time.
