The Great Falls year in pollen
Pollen seasons in Great Falls: tree pollen March to June, grass May to July, and ragweed from early August until the first frost, around September 24.
Tree pollen
Grass
Ragweed
When does ragweed season end in Great Falls?
Ragweed season in Great Falls typically ends with the first frost, around September 24. Some years it comes as early as September 19, some as late as September 29.
A light frost around September 24 knocks the season down; the hard freeze that finishes it usually follows by October 3. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Great Falls 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 Montana page.
Nearby calendars
Frost dates for Great Falls come from the Great Falls International Airport weather station's 30-year records. Season windows reviewed August 2026.