The Utah year in pollen
Tree pollen in Utah runs March to June, grass follows May to July, and ragweed starts in early August and holds on until the first frost — typically around October 22.
When does ragweed season end in Utah?
Ragweed season in Utah typically ends with the first frost, around October 22. The coldest corners of the state see frost by late September; the mildest hold out until late October.
Ragweed keeps releasing pollen until a freeze kills the plants, which is why the season has no fixed end date — it ends when the cold arrives. More on how frost ends ragweed season.
Tree pollen in Utah
Tree pollen in Utah starts in early March, and juniper is usually first out. Mild springs pull the start earlier.
| Tree | Typical season | Heaviest weeks |
|---|---|---|
| Juniper | March to May | mid-March to late April |
| Cottonwood and aspen | March to May | — |
| Maple (boxelder) | March to May | — |
| Birch and alder | April to May | — |
| Pine | May to June | — |
Grass season
Grass pollen in Utah runs May to July, heaviest early June to early July. The culprits are cool-season lawn and meadow grasses — timothy, bluegrass, orchard grass — which flower in one early-summer wave. More on grass seasons.
First frost — and ragweed's end — city by city
The first frost sweeps across Utah over several weeks, and ragweed season ends with it. Based on 30 years of NOAA frost records (1991–2020).
| City | Typical first frost |
|---|---|
| Ogden | October 22 |
| Provo | October 31 |
| Salt Lake City | October 31 |
| St. George | September 29 |
Common questions
When does ragweed season end in Utah?
Ragweed season in Utah typically ends with the first frost, around October 22. The coldest corners of the state see frost by late September; the mildest hold out until late October.
When does allergy season end in Utah?
The last big wave of the Utah pollen year is ragweed, so the season ends with the first frost, around October 22. Tree pollen is done by June, grass mostly by July.
When does tree pollen start in Utah?
Tree pollen in Utah starts in early March, and juniper is usually first out. Mild springs pull the start earlier.
Sources: NOAA U.S. Climate Normals (1991–2020 frost records) · Asthma and Allergy Foundation of America — Ragweed Pollen. Season windows reviewed August 2026.