The Denver year in pollen
Pollen seasons in Denver: tree pollen March to June, grass May to July, and ragweed from early August until the first frost, around October 8.
Tree pollen
Grass
Ragweed
When does ragweed season end in Denver?
Ragweed season in Denver typically ends with the first frost, around October 8. Some years it comes as early as October 3, some as late as October 14.
A light frost around October 8 knocks the season down; the hard freeze that finishes it usually follows by October 18. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Denver pollen year
| Allergen | Typical season |
|---|---|
| Juniper | March to May |
| Cottonwood and aspen | March to May |
| Maple (boxelder) | March to May |
| Birch and alder | April to May |
| Pine | May to June |
| Grass | May to July |
Season-by-season detail is on the Colorado page.
Nearby calendars
Frost dates for Denver come from the Denver-Stapleton weather station's 30-year records. Season windows reviewed August 2026.