Allergy Season Calendar: When Each Pollen Peaks by Region
The U.S. allergy year plays out as three overlapping pollen waves that tag-team from winter to frost. Trees kick things off, usually between February and early summer. Grass picks up the baton around April and lasts through early June. Weeds—ragweed chief among them—finish the relay from August until the first hard frost, according to ACAAI and AAFA.
Exactly when each wave hits depends on where you live, and every region is sliding earlier on the calendar. Southern states can see tree pollen in mid-winter, and Central Texas even has a mountain-cedar stretch that fires up by mid-December. Northern areas still have the shortest season, yet warming winters are lengthening it faster there than anywhere else.
The allergy-season calendar
When tree, grass, and ragweed pollen peak across a typical U.S. year.
The three pollen seasons, in order
Trees release pollen first, typically February through April and into early summer where it stays cool. Grass follows roughly April through early June, hanging on longer where heat lingers. Ragweed and other weeds own late summer into fall: ragweed runs August to first frost, a 6- to 10-week window that crests around mid-September. Allergists note that symptoms can drag on after the pollen stops, so they urge waiting a few weeks post-frost before quitting meds.
Regional differences
Northeastern yards can light up with tree pollen as early as February, swap to grass in late spring, then hand off to ragweed for fall. Southeastern winters are mild enough for tree pollen to start early and for mold to stay nearly year-round. The Midwest sticks to a textbook spring-tree, early-summer-grass, late-summer-ragweed cadence. Parts of the Southwest see juniper and cedar by December, while the Pacific Northwest’s cool, wet winters let alder and birch drift from February well into spring, per regional allergy guidance.
Mold has its own season
Outdoor mold behaves as its own season, the fourth major trigger. Spores climb in warm, muggy stretches and right after rain, with symptoms most common from July to first hard frost. Mold doesn’t die at frost the way pollen does; most spores simply sleep through winter, so a mild, damp fall can keep counts high long after pollen is gone, AAFA notes.
Seasons are getting longer
The allergy calendar is stretching at both ends. A 2021 PNAS study covering 60 North American stations found pollen seasons now begin roughly 20 days earlier and last about 8 days longer than in 1990, with yearly pollen loads up around 21 %. EPA records show ragweed gaining the most ground in northern cities: the season lengthened 21 days in Fargo and 18 days in Minneapolis as first frosts arrive later. The PNAS team linked roughly half of the shift to human-driven climate change, a sign the schedule above is set to keep extending.
Season windows on one axis
Each allergen's typical U.S. window, plus the overlapping outdoor-mold season.
Seasons are starting earlier and lasting longer
earlier start vs. 1990
Anderegg 2021, PNAS
longer season vs. 1990
Anderegg 2021, PNAS
more pollen in the air vs. 1990
Anderegg 2021, PNAS
Check your local pollen forecast
Pollen seasons vary sharply by region. These metros see some of the worst pollen pressure — check the current forecast for each, or look up any US city on the pollen count hub:
- Atlanta, GA pollen count — Mild winters push the tree season early — oak and pine often start in February.
- Austin, TX pollen count — Runs a winter mountain-cedar season most of the country never sees, on top of spring oak.
- Minneapolis, MN pollen count — A short, intense northern season — and one lengthening fastest under a warming climate.
- Houston, TX pollen count — Gulf warmth means little dormancy, so the allergy calendar barely pauses.
- Denver, CO pollen count — High-and-dry timing differs from the coasts; grass and weeds lead the warm months.
- Scranton, PA pollen count — A Northeast valley that runs the full tree-grass-ragweed relay.
Frequently asked
- When does allergy season start?
- Tree pollen leads, generally from February into early summer — earlier in the South, where it can begin in winter. Central Texas even sees mountain cedar by mid-December.
- When is each pollen worst?
- Tree pollen peaks in spring, grass from about April through early June, and ragweed from August to the first frost, peaking in mid-September. Ragweed's window runs 6 to 10 weeks.
- Which months are worst for allergies?
- Two peaks dominate the year: the spring tree-pollen surge and the early-to-mid-September ragweed peak. Where seasons overlap, symptoms can run for months.
- Does mold have an allergy season?
- Yes. Outdoor mold peaks from July to the first hard frost, rising in warm, humid weather and after rain. Unlike pollen, mold does not die at frost; it goes dormant for winter.
- Is allergy season getting longer?
- Yes. Pollen seasons now start about 20 days earlier and run roughly 8 days longer than in 1990, with annual pollen up about 21 % (PNAS).
- Does allergy timing differ by region?
- Strongly. The South starts months before the North, the Southwest sees winter juniper, and the Pacific Northwest's mild wet winters stretch the tree and grass seasons.
More pollen & allergy guides
- Ragweed Allergy: Season, Symptoms, and Where It's Worst
- Hay Fever (Allergic Rhinitis): Causes, Seasons, and Relief
- Pollen Allergy Relief: What Actually Works
- Grass Pollen Allergy: Season, Triggers, and Relief
- Tree Pollen Allergy: Season by Region and the Worst Trees
- Pollen Count Scale: What Low, Moderate, High, and Very High Mean
- Cedar Fever: Texas Mountain Cedar Season, Symptoms, and Relief
- Thunderstorm Asthma: How Storms Trigger Sudden Allergy Attacks
- Oral Allergy Syndrome: Why Pollen Makes Certain Foods Itch
- Mold Allergy: Outdoor Spore Season, Symptoms, and Relief
- Allergies vs. a Cold: How to Tell the Difference
- Allergy Immunotherapy: Shots, Tablets, and Long-Term Relief
- Allergy Testing: Skin Prick, Blood Tests, and What Results Mean
- Kids' Allergies: When They Start, Symptoms, and Safe Relief
- Winter Allergies: Indoor Triggers, Symptoms, and Relief
- Fall Allergies: What Triggers Them and When They Peak
- Dust Mite Allergy: Symptoms, Triggers, and How to Reduce Exposure
- Pine Pollen: Why the Yellow Dust Isn't Your Real Allergy Trigger
- Pollen Calendar: When Tree, Grass, Weed, and Mold Seasons Start and End
- Pollen count by city