The Sioux City year in pollen
Pollen seasons in Sioux City: tree pollen February to May, grass May to July, and ragweed from early August until the first frost, around October 5.
First frost lands around October 5 in Sioux City — about 6 days earlier than Iowa overall — which shifts when ragweed season ends here.
When does ragweed season end in Sioux City?
Ragweed season in Sioux City typically ends with the first frost, around October 5. Some years it comes as early as September 29, some as late as October 11.
A light frost around October 5 knocks the season down; the hard freeze that finishes it usually follows by October 15. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Sioux City 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 Iowa page.
Nearby calendars
Frost dates for Sioux City come from the Sioux City Gateway Airport weather station's 30-year records. Season windows reviewed August 2026.