The St. Louis year in pollen
Pollen seasons in St. Louis: tree pollen February to May, grass May to July, and ragweed from early August until the first frost, around November 4.
First frost lands around November 4 in St. Louis — about 6 days later than Missouri overall — which shifts when ragweed season ends here.
When does ragweed season end in St. Louis?
Ragweed season in St. Louis typically ends with the first frost, around November 4. Some years it comes as early as October 30, some as late as November 9.
A light frost around November 4 knocks the season down; the hard freeze that finishes it usually follows by November 13. Based on 30 years of NOAA frost records (1991–2020).
The rest of the St. Louis pollen year
| Allergen | Typical season |
|---|---|
| Oak | April to May |
| Maple | March to April |
| Elm | February to April |
| Birch | April to May |
| Ash | April to May |
| Hickory and walnut | April to May |
| Grass | May to July |
Season-by-season detail is on the Missouri page.
Nearby calendars
Frost dates for St. Louis come from the St Louis Lambert International Airport weather station's 30-year records. Season windows reviewed August 2026.