The Delaware year in pollen
Tree pollen in Delaware runs March to June, grass follows May to July, and ragweed starts in early August and holds on until the first frost — typically around October 23.
When does ragweed season end in Delaware?
Ragweed season in Delaware typically ends with the first frost, around October 23.
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 Delaware
Tree pollen in Delaware starts in early March, and maple is usually first out. Oak — the bigger problem for most people — follows March to May. Mild springs pull the start earlier.
| Tree | Typical season | Heaviest weeks |
|---|---|---|
| Oak | March to May | early April to early May |
| Maple | March to April | — |
| Birch | March to May | early April to late April |
| Ash | March to April | — |
| Pine | April to June | early May to mid-May |
Grass season
Grass pollen in Delaware runs May to July, heaviest mid-May to mid-June. 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 Delaware over several weeks, and ragweed season ends with it. Based on 30 years of NOAA frost records (1991–2020).
| City | Typical first frost |
|---|---|
| Dover | October 23 |
| Wilmington | November 1 |
Common questions
When does ragweed season end in Delaware?
Ragweed season in Delaware typically ends with the first frost, around October 23.
When does allergy season end in Delaware?
The last big wave of the Delaware pollen year is ragweed, so the season ends with the first frost, around October 23. Tree pollen is done by June, grass mostly by July.
When does tree pollen start in Delaware?
Tree pollen in Delaware starts in early March, and maple is usually first out. Oak — 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.