Gardening on a slope presents challenges, from digging properly aligned holes to plant trees to selecting the best species for the planting site's environmental and cultural conditions. But one of the best ways to control erosion and runoff is by increasing the number of plant roots on a slope; groundcovers such as "Blue Rug" juniper (Juniperus horizontalis "Blue Rug") form spreading mats that keep topsoil in place. Complementary trees also provide protection from wind, water -- or even little feet -- that can damage slopes.
Selecting Companion Trees
When choosing companion trees for your "Blue Rug" juniper, consider varieties that both grow well in hilly conditions and have similar cultural needs. "Blue Rug" is hardy in U.S. Department of Agriculture plant hardiness zones 6 to 8, so select trees that tolerate average annual low temperatures of at least minus 10 degrees Fahrenheit. "Blue Rug" grows best in sunny exposures with well-draining soil; keep tree canopies pruned high so that the juniper can still receive enough sunlight.
For slopes in USDA zones 4 to 7, plant a serviceberry (Amelanchier canadensis). This 15-foot-tall deciduous tree blooms with white and pink flowers in spring, followed by edible black-purple berries. It grows well in sunny, well-draining sites and tolerates a range of soil types. The Japanese yew (Taxus cuspidata) also grows well on slopes. Hardy in USDA zones 5 to 7, this evergreen has dark green needles and grows in sunny sites. It tolerates wet to dry soil and reaches heights of 25 feet.
The red maple (Acer rubrum) also grows well on slopes, according to "Fine Gardening." This 60-foot-tall tree is prized for its fall foliage, which brightens the autumn landscape with shades of red, yellow and orange. Hardy in USDA zones 3 to 9, this adaptable tree thrives in a range of site conditions, from sun to shade and dry to wet soil. Another 60-foot-tall maple, the sycamore maple (Acer pseudo-platanus) also tolerates hilly environments, as well as sandy soil and pollution, making it a good choice for urban sites. This deciduous tree is hardy in USDA zones 4 to 7 and has large, deeply lobed foliage.
White oaks (Quercus alba) grow well on slopes, says the University of Missouri Extension. This deciduous tree is hardy in USDA zones 3 to 8 and grows up to 100 feet tall. It prefers sunny sites with moist, well-draining soil, but tolerates a variety of site conditions. A North American native, the white oak has attractive red fall color and produces nuts that attract wildlife to your yard. The shortleaf pine (Pinus echinata) grows on slopes. This conifer reaches heights to 100 feet with a narrow, 30-foot spread. It's hardy in USDA zones 6 to 9 and grows best in sunny sites. The shortleaf pine has blue-green foliage that complements the blue-green foliage of "Blue Rug."