When to Plant Grass Seed in Washington

Cool-season lawns dominate Washington, and for cool-season seed fall is the better window, with spring the second choice. The dates below are typical crossings from in-state monitoring stations; your city page tracks the live reading.

Best Time to Plant Grass Seed in Washington

Cool-season · fall window

August 24

August 1 (coolest parts) to September 13 (warmest)

For cool-season lawns (fescue, bluegrass, ryegrass), fall is the best time to plant grass seed in Washington, with spring the second choice: fall seedlings face less weed competition and mature before summer heat. The window opens as 2-inch soil falls back through 70°F, and germination slows sharply once soil drops below 50°F, typically around October 19. Fall seeding and fall pre-emergent are an either/or on the same turf; see pre-emergent timing in Washington.

Cool-season · spring window

April 25

April 6 (warmest parts) to May 2 (coolest)

Spring is the second choice: the window opens when soil first holds 50°F and narrows as soil passes 65°F, typically by June 25.

Region	Typical spring window opens	Typical fall window opens	Stations
Eastern Washington	May 2	August 24	2
Central Washington	April 18	—	3

Fall seeding also needs a stop date: new seedlings want about six weeks of growth before frost arrives. Your city page estimates the last safe seeding date from its nearest station: see when to plant in Seattle, when to plant in Tacoma or when to plant in Spokane. Today's statewide reading is on the Washington soil temperature page.

Typical dates are computed from historical 2-inch soil temperature averages at 5 monitoring stations in Washington; your own window depends on your nearest station's readings.

Best Time to Plant Grass Seed in Washington: Month by Month

Typical 2-inch soil temperature by month across Washington, the median of 5 in-state stations with multi-year records, with the seeding verdict for each grass family. Confirm against the current reading on your city page before you put seed down.

Month	Typical 2" soil temp	Cool-season seeding	Warm-season seeding
January	34°F	Dormant	Too cold
February	35°F	Dormant	Too cold
March	40°F	Too cold	Too cold
April	47°F	Too cold	Too cold
May	56°F	Good; fall is better	Too cold
June	63°F	Good; fall is better	Approaching
July	68°F	Risky; heat ahead	Prime window
August	67°F	Soon; still cooling	Too late this year
September	61°F	Prime window	Too cold
October	51°F	Prime window	Too cold
November	39°F	Dormant	Too cold
December	35°F	Dormant	Too cold