Flopping is often frowned upon in the perennial garden (and quickly corrected with bamboo stakes, peasticks, or other mechanisms, if it occurs). Some perennials, however, make a virtue out of laxity, their trailing growth providing the perfect foil to the upright stems of delphiniums, New England asters (Symphyotrichum novae-angliae), and garden phlox (Phlox paniculata). In flower gardens, as in containers, nothing complements a towering thriller better than a contrasting spiller.
Trailing perennials are especially valuable for their ability to knit together other garden elements, upright or otherwise. Mass them at the fringe of a perennial border, and they unify what lies behind them. Position them near a path or patio, and their tumbling stems interrupt and soften the line between hardscape and softscape. And they’re literally made for walls, producing cascades of texture and color that bring the landscape alive.
Margins and walls are not the only places where trailing perennials do their knitting. They excel at covering the voids left by large perennials that go dormant in early summer, such as oriental poppies (Papaver orientale) and bleeding heart (Lamprocapnos spectabilis). Many will thread their stems through upright neighboring perennials, intermingling their contrasting foliage and blooms. Some ground-hugging sprawlers (including creeping thyme, Thymus serpyllum) can even be planted into lawns to form textured, flowering patchworks.
Here’s a sampling of some of the best of these perennial “knitters”.
A native of dry prairies throughout the Central U.S., winecups (Callirhoe involucrata) has just about everything a North American gardener could want, including cold-hardiness (USDA Zones 4-9), drought-tolerance, and a long season of showy blooms. Its lax stems typically form low mats, but will also clamber up neighboring plants or cascade down banks or walls. The bowl-shaped, bright purplish-pink, white-eyed blooms continue for many weeks in summer along new portions of the continually lengthening growth. Several other species of Callirhoe – of various habit – are also well worth growing. All of them prosper in dry habitats.
Moss phlox (Phlox subulata) is so common as to be dismissed by gardeners who should know better. But, just because a plant species is sold at hardware stores and supermarkets (as well as about every other establishment that deals in plants) doesn’t mean that it’s unfit for sophisticated gardens. Hailing from dry slopes and ledges in the East and Central U.S., this needle-leaved evergreen can’t be beat for draping down a wall, or covering a dry slope, or fronting a xeric perennial planting. Its filigreed foliage would be reason enough to grow it, even if it weren’t also a prolific early-spring bloomer. Gardeners who are put off by brassy-flowered forms of this species have any number of subtler cultivars from which to choose. It’s worth considering for any sunny garden within USDA Zones 3 to 9.
Several trailing bellflowers (Campanula spp.) occur on ledges and embankments in European mountains and take well to similar habitats in gardens. Among the most vigorous of the lot is Serbian bellflower (Campanula poscharskyana), which in late spring bears starry blue flowers on low, 3- to 4-foot-wide hummocks. The typically sprawling stems will also clamber or drape, given the opportunity. Plants tolerate a wide range of conditions and may become overly rambunctious in moist, fertile soil. Other bellflowers for edging or walls include Campanula cochlearifolia, C. carpatica, C. garganica, and C. portenschlagiana.
Also from Europe is another trailing perennial that excels on sunny dry slopes: bloody cranesbill (Geranium sanguineum). A variable plant, it typically matures into a sprawling, 6- to 10-inch-tall mound of deeply lobed foliage, decked in late spring and summer with magenta, pink, or white, dark-veined flowers. This hardy (USDA Zones 5 to 9), durable perennial is perhaps at its best in naturalistic plantings, where it can be allowed to seed around into informal colonies.
An excellent geranium for threading through perennials and shrubs is the Geranium ‘Rozanne’, prized for its early-summer-to-frost bounty of purplish-blue flowers. This lanky, 2- to 3-footer will also sprawl obligingly across gaps left by early-dormant perennials.
The legendary garden designer Gertrude Jekyll liked to cover such gaps with the lax, non-climbing growth of , a hybrid between the shrubby Clematis integrifolia and the vining Clematis lanuginosa. Its toppling, 7-foot stems bear a summer-long succession of large starry violet-blue flowers that resemble those of its vining parent. Other clematis for this purpose include Clematis recta, a 5-foot, splaying perennial that envelops itself in summer with small fragrant white flowers; and ‘Mrs. Robert Brydon’, another shrub/vine hybrid whose flopping 8-foot stems carry billowing clusters of pale-blue blooms in August and September.
Hardy perennials for knitting can be planted in fall. Good soil preparation and light mulch will help them become established and protect them through the winter months. Fafard® Premium Natural & Organic Compost should be worked into the soil at planting time and added as a light mulch around newly installed perennials.