Ragweed season: August to the first frost
A single ragweed plant can release a billion grains of pollen, and it doesn't stop on a schedule — it stops when the first freeze kills it. That makes ragweed season's end a date you can actually look up: your area's typical first frost.
How the season works
Ragweed takes its cue from the length of the night: as soon as nights begin to stretch in late July and August, the plants flower and start shedding pollen. Warm, breezy mornings carry it for miles. The season builds to a peak in September nearly everywhere in the country, then rides on until the weather does what no calendar can — the first frost kills the plants, and the season is simply over.
That's the whole trick of this page: "when does ragweed season end" is really a frost question. The dates below come from 30 years of NOAA frost records. Many people plan ahead of the season; if that includes anything medical, ask your doctor.
When ragweed season ends, state by state
| State | Season starts | Typically ends |
|---|---|---|
| Alabama | early August | first frost, around November 11 |
| Alaska | — | no ragweed |
| Arizona | early August | first frost, around December 9 |
| Arkansas | early August | first frost, around November 6 |
| California | early August | first frost, around December 15 |
| Colorado | early August | first frost, around October 8 |
| Connecticut | mid-August | first frost, around October 27 |
| Delaware | early August | first frost, around October 23 |
| District of Columbia | early August | first frost, around November 18 |
| Florida | mid-July | first frost, around January 10 |
| Georgia | early August | first frost, around November 10 |
| Hawaii | early August | fades by late December |
| Idaho | early August | first frost, around September 20 |
| Illinois | early August | first frost, around October 20 |
| Indiana | early August | first frost, around October 21 |
| Iowa | early August | first frost, around October 11 |
| Kansas | early August | first frost, around October 23 |
| Kentucky | early August | first frost, around October 31 |
| Louisiana | early August | first frost, around November 26 |
| Maine | mid-August | first frost, around October 4 |
| Maryland | early August | first frost, around November 4 |
| Massachusetts | mid-August | first frost, around October 21 |
| Michigan | mid-August | first frost, around October 20 |
| Minnesota | mid-August | first frost, around October 1 |
| Mississippi | early August | first frost, around November 19 |
| Missouri | early August | first frost, around October 29 |
| Montana | early August | first frost, around September 26 |
| Nebraska | early August | first frost, around October 13 |
| Nevada | early August | first frost, around October 23 |
| New Hampshire | mid-August | first frost, around October 3 |
| New Jersey | mid-August | first frost, around November 10 |
| New Mexico | early August | first frost, around October 24 |
| New York | mid-August | first frost, around October 25 |
| North Carolina | early August | first frost, around November 4 |
| North Dakota | early August | first frost, around September 27 |
| Ohio | early August | first frost, around October 27 |
| Oklahoma | early August | first frost, around November 4 |
| Oregon | mid-August | first frost, around October 23 |
| Pennsylvania | mid-August | first frost, around October 28 |
| Rhode Island | mid-August | first frost, around October 30 |
| South Carolina | early August | first frost, around November 19 |
| South Dakota | early August | first frost, around October 1 |
| Tennessee | early August | first frost, around November 3 |
| Texas | early August | first frost, around November 29 |
| Utah | early August | first frost, around October 22 |
| Vermont | mid-August | first frost, around October 3 |
| Virginia | early August | first frost, around November 4 |
| Washington | mid-August | first frost, around October 14 |
| West Virginia | early August | first frost, around October 26 |
| Wisconsin | mid-August | first frost, around October 10 |
| Wyoming | early August | first frost, around September 23 |
Common questions
When does ragweed season end?
Ragweed season ends with the first frost, because a freeze kills the plants. That lands anywhere from late September in the far north to December along the Gulf — pick your state below for the typical date near you.
When does ragweed season start?
Ragweed flowers when nights start growing longer — around the start of August in the South, closer to mid-August up north. September is the peak almost everywhere.
Why does frost matter so much for ragweed?
Unlike tree and grass seasons, which wind down gradually, ragweed keeps releasing pollen until cold kills it outright. One clear night at freezing does what the calendar can't — which is why the typical first-frost date is the best answer to "when does this end."
Sources: Asthma and Allergy Foundation of America · American College of Allergy, Asthma & Immunology · NOAA U.S. Climate Normals (1991–2020 frost records)