The Washington year in pollen

When does ragweed season end in Washington?

Ragweed season in Washington typically ends with the first frost, around October 14. The coldest corners of the state see frost by early October; the mildest hold out until mid-November.

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 Washington

Tree pollen in Washington starts in early February, and alder is usually first out. Mild springs pull the start earlier.

Grass season

Grass pollen in Washington 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 Washington 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 Washington?

Ragweed season in Washington typically ends with the first frost, around October 14. The coldest corners of the state see frost by early October; the mildest hold out until mid-November.

When does allergy season end in Washington?

The last big wave of the Washington pollen year is ragweed, so the season ends with the first frost, around October 14. Tree pollen is done by May, grass mostly by July.

When does tree pollen start in Washington?

Tree pollen in Washington starts in early February, and alder is usually first out. Mild springs pull the start earlier.