4Establishment of Vegetation

Most WSDOT projects have 1 to 3 year plant establishment periods. Wetland mitigation projects often include additional years of monitoring to ensure that mitigation standards of success are met. The goal of plant establishment is to promote a healthy, stable plant community.

Soil treatments, such as the use of slow release fertilizer; incorporation of soil amendments such as compost into the soil layer; and surface mulching, may improve the success rate of introduced vegetation. Consult the WSDOT Horticulturist for recommendations. (Check with the local maintenance office or the local jurisdiction's comprehensive plan for any restrictions such as those in well-head protection areas.)

• Use soil amendments based on the soil analysis done for the project. Soil testing is coordinated through the OSC Horticulturist or the Landscape Architect. Soil amendments will enhance the soil's moisture holding capacity.

• Use surface mulches to conserve soil moisture and moderate soil temperatures. Mulches also help keep weeds from competing with desirable plants for water and nutrients, and provide organic matter and nutrients to the soil.

• Use irrigation only when necessary. If irrigation is required, see Chapter 1330 for design guidelines and the Roadside Manual for more detail.

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