Erosion is the gradual wearing away of earth or rock. This is a particular problem on slopes, where water carries bits of earth with it as it runs downhill. Over time, erosion can cause landslides and destruction of property. Plants are a natural way to stabilise slopes and reduce or eliminate erosion. Fast-growing plants with extensive root systems that hold the soil in place are ideal for this purpose. Whenever possible, choose native plants suited for the type of soil and growing conditions on your slope to assure healthy plants and a vigorous root system.
With shallower roots, many perennials stabilise the surface of the soil, keeping topsoil from eroding down the slope. False dragon's head (Physostegia angustifolia) has an extensive root system and spreads rapidly, becoming a groundcover. This herbaceous perennial grows to 5 feet tall. False dragonhead's pink flowers bloom in summer or fall depending on the cultivar. Yarrow (Achillea millefolium) is another herbaceous perennial suitable for stabilising your slope. This hardy plant bears yellow flowers on 3-foot stems, and its extensive, thick root system holds valuable topsoil in place.
Grasses with extensive root systems help stabilise slopes. These grasses also reproduce via their roots and tend to spread rapidly. Sideoats grama (Gouteloua curtipendula) is a warm-season grass that grows to 3 feet tall. Red, orange or yellow flowers bloom from summer into fall, when the foliage turns purple or red. Indiangrass (Sorghastrum nutans) reaches a height of 6 feet. Its green foliage highlights the yellow and purple flowers blooming in late summer.
With deeper roots, many shrubs provide quick slope stabilisation as they grow. California sagebrush (Artemisis californica) has needle-like leaves that release a scent typical of sage. This shrub reaches 5 feet tall and wide, and its white flowers bloom from February to August. Many varieties of sage (Salvia spp.) such as purple sage, black sage and Cleveland sage offer slope stability. These plants have the added benefit of being deer- and rabbit-resistant. Sages grow quickly and bear a wide range of flower colours.
Trees offer the best long-term slope stabilisation because their roots dig deep into the earth to seek water, and smaller rootlets spread throughout shallower ground, preventing runoff. Willows (Salix spp.) such as Scouler, Sitka and Pacific have fibrous, widespread roots and tend to grow quickly. Red alder is another good choice; this tree grows in full sun and prefers moist soil, and reaches at least 80 feet tall.