The Portland year in pollen
Pollen seasons in Portland: tree pollen March to June, grass May to July, and ragweed from mid-August until the first frost, around October 15.
First frost lands around October 15 in Portland — about 11 days later than Maine overall — which shifts when ragweed season ends here.
When does ragweed season end in Portland?
Ragweed season in Portland typically ends with the first frost, around October 15. Some years it comes as early as October 9, some as late as October 21.
A light frost around October 15 knocks the season down; the hard freeze that finishes it usually follows by October 27. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Portland pollen year
| Allergen | Typical season |
|---|---|
| Maple | March to April |
| Birch | April to May |
| Oak | April to June |
| Ash | April to May |
| Pine | May to June |
| Grass | May to July |
Season-by-season detail is on the Maine page.
Nearby calendars
Frost dates for Portland come from the Portland International Jetport weather station's 30-year records. Season windows reviewed August 2026.