The Modesto year in pollen
Pollen seasons in Modesto: tree pollen January to June, grass March to July, and ragweed from early August until the first frost, around December 5.
First frost lands around December 5 in Modesto — about 10 days earlier than California overall — which shifts when ragweed season ends here.
When does ragweed season end in Modesto?
Ragweed season in Modesto typically ends with the first frost, around December 5. Some years it comes as early as November 29, some as late as December 16.
A light frost around December 5 knocks the season down; the hard freeze that finishes it usually follows by December 21. Based on 30 years of NOAA frost records (1991–2020).
The rest of the Modesto pollen year
| Allergen | Typical season |
|---|---|
| Oak | March to May |
| Cypress and juniper | January to March |
| Alder | January to March |
| Olive | April to June |
| Walnut | April to May |
| Grass | March to July |
Season-by-season detail is on the California page.
Nearby calendars
Frost dates for Modesto come from the Modesto City Co Airport weather station's 30-year records. Season windows reviewed August 2026.