The Grand Forks year in pollen
Pollen seasons in Grand Forks: tree pollen February to May, grass May to August, and ragweed from early August until the first frost, around September 27.
Tree pollen
Grass
Ragweed
When does ragweed season end in Grand Forks?
Ragweed season in Grand Forks typically ends with the first frost, around September 27. Some years it comes as early as September 22, some as late as October 1.
A light frost around September 27 knocks the season down; the hard freeze that finishes it usually follows by October 5. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Grand Forks pollen year
| Allergen | Typical season |
|---|---|
| Eastern red cedar | February to April |
| Elm | February to April |
| Maple | March to April |
| Oak | April to May |
| Cottonwood | April to May |
| Grass | May to August |
Season-by-season detail is on the North Dakota page.
Nearby calendars
Frost dates for Grand Forks come from the Grand Forks International Airport weather station's 30-year records. Season windows reviewed August 2026.