The Wisconsin year in pollen

When does ragweed season end in Wisconsin?

Ragweed season in Wisconsin typically ends with the first frost, around October 10. The coldest corners of the state see frost by early 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 Wisconsin

Tree pollen in Wisconsin starts in mid-March, and alder is usually first out. Birch — the bigger problem for most people — follows April to May. Mild springs pull the start earlier.

Grass season

Grass pollen in Wisconsin 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 Wisconsin over several weeks, and ragweed season ends with it. Based on 30 years of NOAA frost records (1991–2020).

Common questions

When does ragweed season end in Wisconsin?

Ragweed season in Wisconsin typically ends with the first frost, around October 10. The coldest corners of the state see frost by early October; the mildest hold out until late October.

When does allergy season end in Wisconsin?

The last big wave of the Wisconsin pollen year is ragweed, so the season ends with the first frost, around October 10. Tree pollen is done by June, grass mostly by July.

When does tree pollen start in Wisconsin?

Tree pollen in Wisconsin starts in mid-March, and alder is usually first out. Birch — the bigger problem for most people — follows April to May. Mild springs pull the start earlier.