The Minnesota year in pollen

When does ragweed season end in Minnesota?

Ragweed season in Minnesota typically ends with the first frost, around October 1. The coldest corners of the state see frost by late September; the mildest hold out until mid-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 Minnesota

Tree pollen in Minnesota 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 Minnesota 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 Minnesota 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 Minnesota?

Ragweed season in Minnesota typically ends with the first frost, around October 1. The coldest corners of the state see frost by late September; the mildest hold out until mid-October.

When does allergy season end in Minnesota?

The last big wave of the Minnesota pollen year is ragweed, so the season ends with the first frost, around October 1. Tree pollen is done by June, grass mostly by July.

When does tree pollen start in Minnesota?

Tree pollen in Minnesota 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.