City	Sow outdoors	Last frost
Seattle	Feb 22 to Mar 22	Mar 8
Spokane	Apr 12 to May 10	Apr 26
Tacoma	Feb 22 to Mar 22	Mar 8
Vancouver	Mar 15 to Apr 12	Mar 29
Bellevue	Feb 22 to Mar 22	Mar 8
Kent	Mar 6 to Apr 3	Mar 20
Everett	Mar 10 to Apr 7	Mar 24
Spokane Valley	Apr 12 to May 10	Apr 26
Renton	Feb 27 to Mar 27	Mar 13
Federal Way	Feb 22 to Mar 22	Mar 8
Yakima	Mar 25 to Apr 22	Apr 8
Kirkland	Feb 22 to Mar 22	Mar 8
Bellingham	Mar 18 to Apr 15	Apr 1
Kennewick	Mar 14 to Apr 11	Mar 28
Auburn	Mar 6 to Apr 3	Mar 20
Pasco	Apr 13 to May 11	Apr 27
Redmond	Feb 22 to Mar 22	Mar 8
Marysville	Mar 10 to Apr 7	Mar 24
South Hill	Mar 28 to Apr 25	Apr 11
Shoreline	Feb 22 to Mar 22	Mar 8
Sammamish	Mar 16 to Apr 13	Mar 30
Richland	Mar 23 to Apr 20	Apr 6
Lakewood	Feb 25 to Mar 25	Mar 11
Lacey	Apr 15 to May 13	Apr 29
Olympia	Apr 15 to May 13	Apr 29
Bothell	Feb 22 to Mar 22	Mar 8
Burien	Feb 16 to Mar 16	Mar 2
Bremerton	Mar 15 to Apr 12	Mar 29
Edmonds	Feb 23 to Mar 23	Mar 9
Puyallup	Mar 28 to Apr 25	Apr 11
Lynnwood	Feb 23 to Mar 23	Mar 9
Lake Stevens	Mar 10 to Apr 7	Mar 24
Issaquah	Feb 27 to Mar 27	Mar 13
Parkland	Feb 22 to Mar 22	Mar 8
Longview	Mar 25 to Apr 22	Apr 8
Wenatchee	Mar 21 to Apr 18	Apr 4
University Place	Feb 25 to Mar 25	Mar 11
Mount Vernon	Mar 10 to Apr 7	Mar 24
Graham	Mar 28 to Apr 25	Apr 11
SeaTac	Feb 16 to Mar 16	Mar 2
Spanaway	Mar 28 to Apr 25	Apr 11
Walla Walla	Mar 13 to Apr 10	Mar 27
Pullman	Apr 22 to May 20	May 6
Des Moines	Feb 16 to Mar 16	Mar 2
Orchards	Apr 12 to May 10	Apr 26
Maple Valley	Apr 6 to May 4	Apr 20
Tumwater	Apr 15 to May 13	Apr 29
Camas	Mar 2 to Mar 30	Mar 16
Moses Lake	Apr 13 to May 11	Apr 27
Mill Creek East	Feb 23 to Mar 23	Mar 9
Mountlake Terrace	Feb 22 to Mar 22	Mar 8
Mercer Island	Feb 27 to Mar 27	Mar 13
Bainbridge Island	Mar 15 to Apr 12	Mar 29
Kenmore	Feb 22 to Mar 22	Mar 8
Frederickson	Mar 28 to Apr 25	Apr 11
Oak Harbor	Feb 27 to Mar 27	Mar 13
North Lynnwood	Feb 23 to Mar 23	Mar 9
Battle Ground	Apr 12 to May 10	Apr 26
Eastmont	Feb 23 to Mar 23	Mar 9
Union Hill-Novelty Hill	Feb 22 to Mar 22	Mar 8
Cottage Lake	Apr 3 to May 1	Apr 17
Hazel Dell	Apr 12 to May 10	Apr 26
Martha Lake	Feb 23 to Mar 23	Mar 9
Bonney Lake	Mar 28 to Apr 25	Apr 11
Arlington	Apr 8 to May 6	Apr 22
Tukwila	Feb 16 to Mar 16	Mar 2
Silver Firs	Feb 23 to Mar 23	Mar 9
Covington	Apr 6 to May 4	Apr 20
Five Corners	Apr 12 to May 10	Apr 26
Ellensburg	Apr 24 to May 22	May 8
Mukilteo	Feb 23 to Mar 23	Mar 9
Silverdale	Mar 15 to Apr 12	Mar 29
Bothell West	Feb 23 to Mar 23	Mar 9
Mill Creek	Feb 23 to Mar 23	Mar 9
Port Angeles	Feb 26 to Mar 26	Mar 12
Monroe	Apr 3 to May 1	Apr 17

Questions

When should I plant swiss chard in Washington?

In Seattle, sow outdoors from February 22 to March 22. Across Washington the window opens between February 16 and April 24, depending on the local last frost.

How is this date worked out?

Sow outdoors from 2 weeks before to 2 weeks after the last frost. Frost dates are NOAA 1991–2020 averages for the weather station nearest each city.