Plants for Retaining Walls

Retaining walls are necessary to hold back soil, but you can soften their look with cascades of decorative plants. Built around raised beds or at the bases of slopes, retaining walls are usually made of brick, stone or other tough materials, and create dry, inhospitable growing conditions. Select plants that thrive in poor, very well-drained soil and grow them in the retained earth along the tops of the walls or in soil-filled gaps in old, weathered walls.

Bright, dry spots along the tops of retaining walls in full sun are where pussytoes (Antennaria dioica) and speedwell (Veronica liwanensis) thrive. Hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8, pussytoes grows 3 to 9 inches tall and 9 to 18 inches wide, and bears white to pale pink flowers resembling cats' paws in spring through early summer. Speedwell is hardy in USDA zones 4 through 9 and bears blue spring flowers on mats of glossy green foliage 1 inch tall and 18 to 24 inches wide. Both of these perennials tolerate dry, rocky soil and drought, and speedwell is disliked by deer and rabbits.

Plants that grow at the top edges of shady retaining walls create a rustic, woodland look. Alpine barrenwort (Epimedium alpinum) forms clumps 6 to 9 inches tall and 9 to 12 inches wide. In spring its foliage is tinged pink and decorated with spikes of dull red flowers, and in fall its leaves turn deep, reddish-bronze. Another shade lover for growing on retaining walls is bigroot geranium (Geranium macrorrhizum). Bearing purple-pink flowers in spring through early summer, this perennial grows 12 inches tall and 24 inches wide, and its fall foliage develops red tones. Both plants are hardy in USDA zones 4 through 8.

Sprawling plants cascade down retaining walls. Silver ponysfoot or silver nickel vine (Dichondra argentea 'Silver Falls'), which is hardy in USDA zones 10 through 12, creates an evergreen silver waterfall-like effect when planted at the tops of retaining walls, growing 3 to 6 feet long and 4 inches wide. Thriving in dry soil and full sun, over time the trailing perennial spreads sideways through stem nodes. Rose verbena (Glandularia canadensis) -- also called clump verbena or rose vervain -- grows 6 to 18 inches tall and sprawls 12 to 24 inches wide. Bearing rose-pink to rose-purple blooms in late spring through late summer, rose verbena can self-seed in its preferred full-sun sites and dry soil, and is hardy in USDA zones 5 through 9.

Growing annual plants in retaining walls allows new displays every year. Clean out gaps in the walls, fill them with well-drained potting soil, and sow annual flower seeds after the last average frost date. Moss rose (Portulaca grandiflora) grows 3 to 9 inches tall and 6 to 12 inches wide, and blooms from summer through the first frost in a range of colors including white, yellow, orange and rose. Creeping zinnia (Sanvitalia procumbens) bears purple-brown-centered, yellow daisy flowers summer through fall. Growing 3 to 6 inches tall, creeping zinnia spreads 9 to 18 inches wide or wider. Both plants thrive in full-sun sites.