In Puget Sound, we run across so many different landscapes, including a significant amount of steep slopes and bluffs. As an environmental company who is also a general contractor, we perform invasive weed management and native plant restoration, especially on slopes and after landslides. Often times installing traditional erosion control fabric on these steep bluff is very difficult, and can cause further soil loss. Erosion control fabric is really designed for engineered slopes that are a single plane, not undulating like our natural bluffs. Instead, we use hydroseeding to prevent erosion and start an initial seed bank on these steep slopes and landslide areas.
Hydroseeding is especially conducive for steep slopes and landslide areas but is also very effective for erosion control on flat ground and for creating and restoring native lawns.
Photo 1 and Photo 2: Examples of hydroseeding on steep slopes.
Our seed mix includes a combination of native woody, herbaceous, and grass seeds. Our native seed mixes stands us apart from the majority of hydroseeding that sprays non-native grasses. The overall hydroseed application includes four components: native seeds, mulch, water, and mycorrhizae (we use FungiPerfect MycoGrow).
Spring (April through June 30) and fall (from September 1 through October 1) are the ideal times for applications. Seeding that occurs between July 1 and August 30 will require irrigation.
We have approximately 200 feet of hose that can reach the inaccessible and remote slopes. Hydroseed is applied both from the top of the slope and from the bottom, as allowed. Natural rainfall or supplemental irrigation are a necessary for an effective hydroseed application.
On very steep slopes and near-vertical areas, the mulch comes in the form of a bonded fiber matrix (BFM) or hydraulic mulch to stick the hydroseed to the slope and provide a substrate for initial growth. Bonded fiber matrix is an engineered wood fiber mulch with added polacrylamides, guar gums, and synthetic fibers to reinforce the matrix once cured. BFM is generally more effective than rolled fabrics covering a slope, especially natural, non-engineered slopes with uneven surfaces and some remaining vegetation.
Hydroseeding immediately bonds to the soil surface. The spray application allows mulch to fill the gaps and contour to the surface providing natural water breaks to decrease flow and increase water retention on the slope. The rough grading holds the seed and mulch in place so there is more consistent germination.
Additional hydroseeding benefits include:
When hydroseeding on very sandy slopes that are somewhat uniform, another option is to install an engineered, rolled matrix prior to hydroseeding that provides an additional substrate for the hydraulic mulching to bond and adhere to. This matrix remains on the slope and becomes interwoven with roots of native plants.