Sowing a mix of appropriate seed into well-drained, fertile soil that receives plenty of sun is the best way to ensure the success of your lawn. Western Washington's summers are dry, so take advantage of the winter moisture as soon as the weather warms up.
According to the Washington State Nursery and Landscape Association, early April to late May is the best time to plant grass seeds. This allows the grass to take advantage of spring rains and warmth to become established before the dry season sets in.
The University of Washington's Botanic Gardens recommends a 90 percent mix of tall fescue and perennial rye for the western Washington lawn, and various bentgrasses flourish as well. Avoid bluegrass, Bermuda and Saint Augustine grass. While buffalo grass is common in eastern Washington, it does not do well west of the Cascades.
Tips for Success
Mix organic matter into heavy clay soil to add structure before sowing. Do not spread general pesticides, which kill beneficial insects as well as pests. Perform frequent light waterings instead of infrequent soakings to encourage deep root growth, and use compost or manure instead of chemical fertilizer. Set your mower blade high and leave the grass clippings on the ground to add nitrogen back to the soil.