The Michigan year in pollen
Tree pollen in Michigan runs March to June, grass follows May to July, and ragweed starts in mid-August and holds on until the first frost — typically around October 20.
When does ragweed season end in Michigan?
Ragweed season in Michigan typically ends with the first frost, around October 20. The coldest corners of the state see frost by mid-October; 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 Michigan
Tree pollen in Michigan starts in mid-March, and alder is usually first out. Maple — the bigger problem for most people — follows March to May. Mild springs pull the start earlier.
| Tree | Typical season | Heaviest weeks |
|---|---|---|
| Birch | April to May | late April to mid-May |
| Oak | April to June | early May to late May |
| Maple | March to May | — |
| Alder | March to April | — |
| Ash | April to May | — |
| Pine | May to June | — |
Grass season
Grass pollen in Michigan 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 Michigan over several weeks, and ragweed season ends with it. Based on 30 years of NOAA frost records (1991–2020).
| City | Typical first frost |
|---|---|
| Detroit | October 31 |
| Grand Rapids | October 20 |
| Lansing | October 13 |
| Marquette | October 21 |
| Traverse City | October 16 |
Common questions
When does ragweed season end in Michigan?
Ragweed season in Michigan typically ends with the first frost, around October 20. The coldest corners of the state see frost by mid-October; the mildest hold out until late October.
When does allergy season end in Michigan?
The last big wave of the Michigan pollen year is ragweed, so the season ends with the first frost, around October 20. Tree pollen is done by June, grass mostly by July.
When does tree pollen start in Michigan?
Tree pollen in Michigan starts in mid-March, and alder is usually first out. Maple — the bigger problem for most people — follows March to May. 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.