The Seattle year in pollen
Pollen seasons in Seattle: tree pollen February to May, grass May to July, and ragweed from mid-August until the first frost, around November 17.
First frost lands around November 17 in Seattle — about 34 days later than Washington overall — which shifts when ragweed season ends here.
When does ragweed season end in Seattle?
Ragweed season in Seattle typically ends with the first frost, around November 17. Some years it comes as early as November 10, some as late as November 24.
A light frost around November 17 knocks the season down; the hard freeze that finishes it usually follows by December 2. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Seattle pollen year
| Allergen | Typical season |
|---|---|
| Alder | February to April |
| Birch | March to May |
| Cottonwood | March to May |
| Oak | April to May |
| Grass | May to July |
Season-by-season detail is on the Washington page.
Nearby calendars
Frost dates for Seattle come from the Seattle Boeing Field weather station's 30-year records. Season windows reviewed August 2026.