The South Dakota year in pollen
Tree pollen in South Dakota runs February to May, grass follows May to August, and ragweed starts in early August and holds on until the first frost — typically around October 1.
When does ragweed season end in South Dakota?
Ragweed season in South Dakota 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 early 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 South Dakota
Tree pollen in South Dakota starts in mid-February, and eastern red cedar is usually first out. Mild springs pull the start earlier.
| Tree | Typical season | Heaviest weeks |
|---|---|---|
| Eastern red cedar | February to April | early March to early April |
| Elm | February to April | — |
| Maple | March to April | — |
| Oak | April to May | mid-April to early May |
| Cottonwood | April to May | — |
Grass season
Grass pollen in South Dakota runs May to August, heaviest mid-May to early July. Cool-season grasses flower in the first wave; warm-season grasses like Bermuda pick up through summer, which stretches the season. More on grass seasons.
First frost — and ragweed's end — city by city
The first frost sweeps across South Dakota over several weeks, and ragweed season ends with it. Based on 30 years of NOAA frost records (1991–2020).
| City | Typical first frost |
|---|---|
| Aberdeen | September 26 |
| Rapid City | October 1 |
| Sioux Falls | October 6 |
Common questions
When does ragweed season end in South Dakota?
Ragweed season in South Dakota 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 early October.
When does allergy season end in South Dakota?
The last big wave of the South Dakota pollen year is ragweed, so the season ends with the first frost, around October 1. Tree pollen is done by May, grass mostly by August.
When does tree pollen start in South Dakota?
Tree pollen in South Dakota starts in mid-February, and eastern red cedar 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.