The San Francisco year in pollen
Pollen seasons in San Francisco: tree pollen January to June, grass March to July, and ragweed from early August, fading out by late November.
Unlike most of California, San Francisco rarely sees a real frost, so ragweed fades out rather than stopping cold.
Tree pollen
Grass
Ragweed
When does ragweed season end in San Francisco?
Ragweed around San Francisco winds down on its own through late November — most winters never bring a season-ending freeze.
The rest of the San Francisco 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 San Francisco come from the San Francisco Dwtn weather station's 30-year records. Season windows reviewed August 2026.