Planting on a slope can be problematic, depending on how steep it is. A slope of more than 17 degrees is likely to have soil erosion and stability problems, according to the British conservation group BTCV, and will be hard to work. Select shrubs with roots that spread wide and deep. The stronger the root system, the more soil it can grab and stabilise. Plant creeping or smaller shrubs to preserve the view, or taller, spreading varieties to block it. Be sure to choose shrubs that are low-maintenance and won't require heavy cultivation or pruning.
Small evergreens are excellent candidates for planting on slopes. Creeping juniper hugs the ground, spreading blue-green branches over a wide area, reducing weeds and the need for mowing while stabilising the soil. Yews are incredibly hardy, drought-resistant and adaptable to poor soils. Sargent juniper also has a low, mounding habit and survives well without supplemental watering or fertiliser.
Serviceberry, red chokeberry and elderberry have a wilder growing habit, reaching a height and spread of 10 to 15 feet. They also provide an abundance of food for birds and small animals. These shrubs can cover and spread over a hillside in a short time and have extensive root systems. They need no maintenance other than occasional removal of seedlings and new plants.
If you want your slope to be decorative as well as stable, several flowering shrubs will grow well there. Mock-orange has white, extremely fragrant blossoms that pop in early June. Mountain laurel has glossy, green leaves and a less showy flower. Red alder, bush honeysuckle and burning bush round out the summer and fall with colourful foliage. All of these taller shrubs have deep tap roots and are extremely cold and drought-resistant. Burning bush and mock orange may require light pruning for deadwood and to control overcrowding.