The Casper year in pollen
Pollen seasons in Casper: tree pollen March to June, grass May to July, and ragweed from early August until the first frost, around September 22.
Tree pollen
Grass
Ragweed
When does ragweed season end in Casper?
Ragweed season in Casper typically ends with the first frost, around September 22. Some years it comes as early as September 15, some as late as September 28.
A light frost around September 22 knocks the season down; the hard freeze that finishes it usually follows by October 2. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Casper 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 Wyoming page.
Nearby calendars
Frost dates for Casper come from the Casper Natrona Co Airport weather station's 30-year records. Season windows reviewed August 2026.