Choosing plants for a sloping area can test even experienced gardeners. Steep slopes generally experience increased runoff and soil erosion, conditions that make it difficult to establish plants. Slopes often have the added challenge of poor, dry soil. To plant a successful slope garden, choose hardy, low-maintenance plants. Along with the aesthetic value plants provide, their roots also help prevent erosion and runoff. Add a layer of jute netting to help young plants remain in place while they become established.
The University of Minnesota Extension recommends hardy, self-seeding and quick-spreading ornamental grasses for slopes. Choices include little bluestem (Schizachyrium scoparium). This grass grows from 2 to 4 feet tall in an upright, spreading form. Little bluestem has bright blue foliage that turns orange in fall. It is hardy in U. S. Department of Agriculture plant hardiness zones 4 to 10 and prefers sun and dry to well-drained and poor soil.
Switch grass (Panicum virgatum) grows up to 6 feet tall and is hardy in zones 5 to 9. This dense, clumping grass attracts wildlife with its red seeds and produces red to purple flowers in fall. Plant in sun to partial shade and a range of soils, from moist to dry.
Once established, shrubs form the backbone of slope landscaping. The University of Minnesota includes the low-growing creeping juniper (Juniperus horizontalis) and spreading Japanese yew (Taxus cuspidata) among its list of the best shrubs for slopes. The creeping juniper is hardy in USDA zones 5 to 8 and grows to 2 feet tall with an 8- to 10-foot spread. This evergreen has scalelike foliage and tolerates poor soil. Plant in full sun. The Virginia Cooperative Extension also recommends this shrub for slopes.
The Japanese yew, a slow-growing evergreen, reaches heights of 6 feet with a 7-foot spread. Hardy in zones 4 to 8, this shrub tolerates sun to shade and a range of soils. It tolerates drought, cold and urban pollution and has dense, compact foliage.
The University of Minnesota Extension and the Virginia Cooperative Extension recommend hostas (Hosta spp.). These versatile perennials grow from 4 inches to 4 feet tall and are hardy in zones 3 to 8. Hostas tolerate partial to full shade and produce white to purple flowers, though they are primarily grown for their large, variegated foliage.
Other "best" perennials for slopes include the violet (Viola spp.), a 4- to 8-inch-tall plant that flowers with purple, blue and white spring flowers. Violets spread quickly and are hardy in zones 4 to 9. They prefer well-drained soil and sun to full shade.
Vines help to stabilise a slope when grown prostrate as ground covers. The North Carolina State University Cooperative Extension recommends the sweet autumn clematis, which grows quickly to 30 feet long. This deciduous vine prefers sun to partial shade and tolerates a range of soils. Clematis vines are hardy in zones 4 to 9 and bloom with fragrant, white flowers in late summer through early fall. They reseed themselves.
The extension also recommends English ivy for slopes. This evergreen vine spreads to 50 feet and comes in a variety of cultivars. Hardy in zones 6 to 8, English ivy grows well in partial to full shade and tolerates a range of soils. Mature vines produce blue-black berries. Protect from winter sun.
- University of Minnesota Extension; The Best Plants for 30 Tough Sites; Mary Meyer, et al.; 2007
- Virginia Cooperative Extension; Selecting Landscape Plants: Ground Covers; Diane Relf, et al.
- North Carolina Cooperative Extension Service; Plants for Steep Slopes; T.E. Bilderback
- Washington State University; Gardening on Steep Slopes; April 2005
- Carson Clear Water Revival; Stabilize Steep Slopes with Plants and Erosion Control; John Cobourn, et al.
- NC State University; Ornamental Grasses; Erv Evans