By Joe Julian, Colorado State University Cooperative Extension Agent, Horticulture and Entomology
Erosion is Mother Nature's challenge to Colorado homeowners. When we alter the landscape, we encourage erosion, which can remove valuable topsoil, pollute water supplies and damage property.
Erosion can be prevented in most situations. Re-vegetation or stabilization with existing plants often is the answer for slopes with a 25 percent or less incline. Steeper slopes may require more sophisticated erosion control methods.
Grass seeding is an inexpensive and relatively quick way to stop erosion on gradual slopes. Consider hiring a re-vegetation specialist or landscape contractor who can seed with a drill. Drilling embeds the seeds into the soil so they don't erode or blow away. Common grasses that will control erosion are smooth brome, Timothy, meadow foxtail, wheatgrass varieties (pubescent, intermediate, slender) and fescue varieties (chewings, red, hard, sheep).
Smooth brome is a good sod-forming grass with exceptional seedling vigor. Timothy is a persistent bunch grass that prefers moist sites. Meadow foxtail, which features an attractive, fluffy seed, grows at higher elevations. Most wheatgrass varieties do well on dry sites, but they are not well adapted above 10,000 feet. Fescues are hardy and adaptable with root systems that hold soil on slopes. A mixture of fescue and crested wheat has proven successful in stopping erosion. In addition, seed companies, nurseries and feed stores sell grass seed mixtures especially developed for erosion control. All of these grasses initially need water -- either natural or supplemental.
Planting time depends on availability of water. Without irrigation, you'll need to plant seeds late in the fall, but before the ground is frozen. If seeds are planted too early in fall, they will germinate and the seedlings could be frost-killed.
April and May planting, following a snow melt, is another option. June is too late. Too little moisture, combined with summer heat, would destroy the growing seedlings. Irrigation gives you more flexibility in planting. You'll need to water 2-3 times per day during germination (approximately 2 weeks). Frequent, light waterings are best until grasses are established. Apply a high phosphorous starter fertilizer before seeding. Use 5 lbs./1000 square feet to establish seedling roots quickly. Don't use more, however, as excessive fertilizer will wash away and can pollute water sources.
Mulching encourages a successful re-vegetation. Mulches can hold seed and fertilizer in place, keep the soil moist and shade seedlings. Straw, wood chips, pine needles and wood fibers are common mulching materials. Apply mulch at 1-2 inches thick so seedlings can penetrate. On steeper slopes, use netting made of jute, excelsior, fiberglass or plastic. Such netting will prevent seeds and soil from washing away during Colorado's heavy rain storms.
You can use certain ground covers to control erosion on steeper slopes. Crown vetch is one of the best options. It is used on dry, infertile soils common to mountain landscapes. Plant crown vetch in the fall, so roots can develop, allowing vegetative parts to grow rapidly the following spring. Crown vetch reaches 12-18 inches tall and features an attractive pink flower from June until fall.
Weeping forsythia is another ground cover for steep banks. This plant spreads densely, grows well in most soils and reaches 3-4 feet high.
Several creeping juniper varieties also are effective on steep slopes. These include Andorra, Bar Harbor, Plumosa and Wilton. Sargent Juniper, although not a creeping variety, also is an option. All of these junipers do well in full sun and all prefer well-drained soils.
Other plant varieties and tactics, such as terracing (shown at right), can help control erosion.
Photo: Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010