Steep slopes present a conflict between erosion control and fire suppression. To control slope failure, plantings need to have deep strong root systems to "key" the soil into the underlying bed rock. Superficial plantings of Ivy, Iceplant or hydroseeded grasses and small perennials will not accomplish this slope stabilization. On the other hand, fire suppression considerations work in the opposite direction. It is desirable to put as little woody plant material on the slope as possible to not provide potential fuel.
Proper choice of plant materials strikes a balance between these two concerns. Woody plant species with deep roots are chosen that have some fire retarding or low fuel / low profile characteristics. The actual plant choice also depends upon thickness and stability of the soil and orientation of the slope to the sun.
Also, besides planting, surficial erosion protection will be needed to stop surface erosion until the new plantings provide soil cover. This can be accomplished by hydroseeding with a glue or with jute meshing. Hydroseeding is cheaper but far less reliable. Intense rains can weaken and erode hydroseeding, if the seed doesn¹t have slow even rainfall to help germinate prior to heavy downpours. Germination can also be spotty and plant selection is limited. Jute mesh and other geotextiles give immediate coverage and will last a year or two before they biodegrade.
Slope plantings for fire and erosion control require maintenance and take some time to establish. Upon planting it will take somewhere between 2-5 years for the root systems of the new plantings to "lock" into the underlying bedrock. Because of this time lag it is usually imperative to leave existing brush in at least until the new plantings mature. They can be cut back but should not be rooted out or killed.
It is important that the homeowner understand that these plantings will require maintenance to maximize the fire preventative nature of the plantings. Annual maintenance must be done to eliminate deadwood, lower profile of planting, and remove weeds. After establishment, plantings should be watered 1-4 times monthly to keep water content in leaves high, to resist burning.
For more information please contact the author at:
Robert Cornell & Associates, Inc.
Landscape Design & Installation
1211 Sinaloa Avenue
Pasadena CA 91104
phone 626.398.5581 fax 626.398.4421