Can I plant groundcovers, shrubs, and trees to stabilize a steep slope?
There are several resources which will help you in
selecting plants to prevent erosion and mudslides on
your slope.
Please note that these articles are merely suggestions and should not be construed as advice. We are librarians, not engineers!
None of our standard books on trees mentions the soil binding quality of tree roots. However, the Miller Library does have very good technical books and articles on slope stabilization. (For example, Slope Stabilization and Erosion Control: A Bioengineering Approach, edited by R.P.C. Morgan and R.J. Rickson, 1995.)
I do want to note one thing that many articles mention: no amount of established vegetation will hold a steep slope if other forces are present that would contribute to a landslide.
The Department of Ecology website has a list of appropriate plants.
Additionally, there are a number of books with
information on the subject. Vegetative Contribution
to Slope Stability at Magnolia Park (by Kathy Parker, 1996)
recommends Oregon grape (Mahonia), which she suggests
for gentle slopes.
Other smaller plants she lists are:
Polystichum munitum (native sword fern)
Vaccinium ovatum (evergreen huckleberry)
Symphoricarpos albus (snowberry)
Larger shrubs in her list:
Alnus rubra (red alder)
Philadelphus lewisii (mock orange)
Sambucus racemosa (red elderberry)
Small trees:
Acer circinatum (vine maple)
Amelanchier alnifolia (serviceberry)
Corylus cornuta (hazelnut)
For steeper slopes, Parker says that they may not be
good candidates for vegetative rehabilitation unless
you put in some kind of structure. She says that Jute mats can be used in conjunction with native seed, mulch, and shrubs, if carefully anchored. She also mentions a Weyerhaeuser product called Soil
Guard.
Steep Slope Stabilization Using Woody Vegetation (by
Leslie Hennelly, 1994) has a plant list, as well as a chart which indicates plants used to control erosion, the degree
of the slopes, and the rate of success in resisting
erosion.
Two titles which focus more on the garden design
aspect of planting on a slope are
Hillside Gardening : Evaluating the Site, Designing
Views, Planting Slopes (by William Lake Douglas, 1987) and
Hillside Landscaping (by Susan Lang and the editors
of Sunset Books, 2002).