Fall Pollen Season: Ragweed, Mold, and What to Expect

Why Ragweed Owns the Fall

One ragweed plant can release a billion pollen grains in a single season. The grains are light and dry, built to ride the wind, and they turn up hundreds of miles from the nearest plant. Ragweed has even been found 400 miles out to sea and two miles up in the atmosphere. You do not need ragweed in your yard to feel it.

There are 17 species of ragweed in North America, and they grow in all 48 contiguous states. That reach is what makes fall allergies so hard to escape. Grass pollen fades after the summer peak, and ragweed steps right in.

Ragweed is not the only offender. Mold spores climb in fall as fallen leaves pile up and stay damp, and other weeds pitch in depending on where you live. But if your worst weeks land in September, ragweed is almost certainly the cause.

The Weeds and Molds Behind Fall Allergies

Ragweed leads, but a handful of other plants and outdoor molds add to the pollen and spore load through fall. Here are the main ones tracked across US regions:

Mold is the one people forget. Raking a pile of wet leaves sends a cloud of spores into the air, and a damp, mild fall keeps outdoor mold high well into November. If your symptoms spike on yard-work days rather than sunny windy ones, mold may be as much to blame as ragweed.

When Fall Pollen Season Starts and Ends

Ragweed takes its cue from shorter days, so it starts within a week or two of mid-August almost everywhere. The end is what shifts by region, because it depends on your first hard frost:

• Northern states (Minnesota, Wisconsin, New England): Ragweed starts mid-August, peaks early September, and usually ends by early to mid-October when frost arrives.
• Midwest and Mid-Atlantic (Illinois, Ohio, Virginia): Peaks in September and often runs through late October. This region has some of the highest ragweed counts in the country.
• Southeast (Georgia, the Carolinas, Tennessee): A long season, mid-August into November, because frost comes late.
• Gulf Coast and Deep South (Texas, Louisiana, Florida): Ragweed can hang on into December where a hard frost may not come at all.

Fall seasons are also getting longer. Warmer temperatures have pushed the first frost later, and a 2021 analysis in the Proceedings of the National Academy of Sciences found North American pollen seasons now start earlier and run about 20 days longer than they did in 1990. For the full end-of-season breakdown, see when does ragweed season end.

Fall Allergy Symptoms vs. a Cold

Fall allergies and the season's first cold feel a lot alike, and they show up at the same time of year. Here is how to tell them apart:

Ragweed pollen brings the whole range of allergy symptoms. For a closer look at specific reactions, see can pollen cause a sore throat, pollen-related coughing, and why pollen makes your skin itch. About one in three ragweed sufferers also reacts to certain raw foods like bananas, melon, and zucchini, a cross-reaction called oral allergy syndrome.

How to Manage Fall Pollen Allergies

You can't wait out ragweed the way you might a short tree-pollen burst. It runs for two to three months. The move is to cut your exposure and treat symptoms before they build.

Start medication in early August

Daily antihistamines like cetirizine (Zyrtec) or loratadine (Claritin) work best when you start before symptoms do. Begin a week or two ahead of your region's mid-August ragweed start. A steroid nasal spray like fluticasone (Flonase) helps with congestion, and it also takes a few days to reach full effect, so start it early too.

Time your outdoor plans

Ragweed pollen peaks from mid-morning to midday. Early morning right after sunrise and the hours after rain are your cleaner windows. If you run or walk, aim for those. See the best time of day to go outside for the full daily curve.

Keep pollen out of the house

• Keep windows closed on High and Very High pollen days
• Shower and change clothes after being outside
• Run a HEPA air purifier in your bedroom
• Wear a mask when raking leaves or mowing, which stirs up both pollen and mold

Ask about allergy shots for the long run

If ragweed wrecks every September and medication isn't enough, allergy shots or under-the-tongue tablets can retrain your immune system over time. That's a conversation for an allergist. You can find an allergist in your state to get started.

What Pollen Levels Mean for Your Symptoms

MyPollenPal rates pollen severity from None to Very High. Here is what each level tends to mean once ragweed is in the air:

Check Fall Pollen Levels in Your City

Ragweed counts swing hard from city to city and day to day. A High day in Kansas City doesn't tell you what's happening in Atlanta. The only way to know what's in your air is to check your local data.

Here are cities where fall ragweed hits hardest:

Browse all cities or search by ZIP code to find your local pollen report.

Want to see which cities are getting hit hardest right now? Check today's worst pollen cities.

Sources

• American College of Allergy, Asthma & Immunology (ACAAI). "Ragweed Allergy." acaai.org
• Asthma and Allergy Foundation of America (AAFA). "Seasonal Allergies (Rhinitis)." aafa.org
• American Academy of Allergy, Asthma & Immunology (AAAAI). "Allergen Immunotherapy." aaaai.org
• Anderegg WRL, Abatzoglou JT, Anderegg LDL, et al. "Anthropogenic climate change is worsening North American pollen seasons." Proc Natl Acad Sci USA. 2021;118(7):e2013284118. doi:10.1073/pnas.2013284118

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