Seed Starting Calendar for Washington

Count back from the median last frost where you garden. At Spokane (Spokane Intl Airport) that date is April 26, so for spring 2027 onions start indoors Jan 18 to Feb 1, peppers Mar 1 to Mar 15 and tomatoes Mar 8 to Mar 22. Across Washington's 152 NOAA stations the median last frost runs from Mar 12 to May 22 for the middle 90 percent, so a garden near Davenport starts later than one near Olga 2 SE.

It depends on the station. The earliest median last spring freeze in Washington is February 26 at Olga 2 SE; the latest is June 6 at Davenport. A median is a coin flip: at Spokane the last 32°F freeze comes after April 26 in half of years, and has passed by May 10 in 9 of 10 years (NOAA 1991 to 2020 normals).

UNH Extension sets tomatoes out 1 to 2 weeks after the last frost, which at Spokane is May 3 to May 10 in 2027. Tomatoes are frost tender, so the date to watch is May 10, when 9 of 10 springs at Spokane have had their last 32°F night. Hardening off starts two weeks before setting out (Apr 19 to May 3).

Washington State University Extension publishes planting months by region (Pacific Northwest). For Pacific Northwest, tomatoes go in during June. Seeds for transplants go in 4 to 10 weeks ahead of those months, depending on the crop.

Washington State University Extension's Home Vegetable Gardening in Washington puts it this way: "Determine when to sow each vegetable seed by selecting the date you intend to transplant to your garden; count backwards on your calendar the approximate number of weeks needed to grow that vegetable (see Table 4)." The guide is linked below with the date it was read (September 21, 2026).

UNH Extension gives 8 to 10 weeks from seed to transplant for both, and sets peppers out 2 weeks after the last frost and eggplant 2 to 3 weeks after, so the sowing date is 6 to 8 weeks before the median last frost. At Spokane that is Mar 1 to Mar 15 for peppers.

About two weeks. University of Missouri Extension: "Hardening should be started about two weeks before planting in the garden." University of Minnesota Extension adds that seedlings should go out on a cloudy day or in the late afternoon.

Seattle on Puget Sound reaches its median last frost around Mar 13, Walla Walla and Vancouver in late March, Spokane around Apr 26, and Yakima around May 8, east of the Cascades. Each station carries its own dates: Seattle Mar 13 and Yakima May 8 at the median.