The year-round allergy calendar
Month by month: what's in the air, where the peaks fall, and when you actually get a break. Useful for planning vacations, outdoor events, and knowing when to refill your prescription before you need it.
The short answer
For most of the continental US, the allergy-free window is roughly November through January — the three months when hard frosts have killed the weed pollen and tree pollen hasn't started yet. Everything else is some combination of tree, grass, weed, or mold season. The specific months depend heavily on latitude and climate; the calendar below shows typical ranges for the mid-Atlantic and Midwest, with notes on how it shifts in warmer and cooler regions.
If you want the real-time picture for your location, the home page shows today's reading and a five-day forecast.
Month-by-month calendar
Low One of the quietest months of the year. Most of the country is well below freezing and pollen production is dormant. Exception: southern Texas, Florida, and coastal California, where mountain cedar, juniper, or alder may already be releasing pollen in warm winters. If you live in the Deep South and feel like you have a cold that won't quit in January, it might be cedar.
Tree Tree pollen begins in the South. Cedar fever peaks in central Texas — January through February is the worst window, and it can be debilitating. In the mid-Atlantic and Southeast, elm, alder, and hazel start releasing. Most of the Midwest and Northeast are still dormant, though warm years push the start earlier every decade.
Tree Tree season opens across most of the country. Maple, elm, alder, and ash lead the charge. In the Southeast, oak is already building. This is when many people who "don't have allergies" start noticing symptoms for the first time — the counts climb fast. Mountain cedar continues in the Southwest.
Tree Peak tree season for most of the country. Oak, birch, and pine dominate. The yellow-green film on cars and patio furniture in April is almost always oak pollen — it's produced in enormous quantities and is highly allergenic. This is typically the highest-count month of the year for the Eastern US. Counts are highest on warm, dry, breezy mornings.
TreeGrass The handoff month. Tree pollen begins winding down as grasses start releasing. Timothy and orchard grass begin in the South; Kentucky bluegrass follows in the Midwest and Northeast. For anyone allergic to both trees and grasses, May can feel relentless — the combined load is higher than either season alone.
Grass Peak grass season. Timothy, ryegrass, Kentucky bluegrass, Bermuda, and Johnson grass are all active. Bermuda dominates in the South and Southwest. In humid climates, mold spores also start climbing after wet periods. Daily counts peak between 10 AM and 3 PM on warm, breezy days.
GrassMold Grass counts remain elevated, especially in Southern states where Bermuda grass runs through August. Mold spores spike after summer thunderstorms. In the hottest, driest parts of the country (Southwest, High Plains), both pollen and mold can be suppressed by heat — but a wet July reverses that. Generally a transitional month heading toward weed season.
WeedMold Ragweed begins. The most allergenic weed pollen in North America starts releasing in early August — later in the Upper Midwest and Canada, earlier in the South. Mold also peaks in August after the summer wet season. For the roughly 15–20% of Americans allergic to ragweed, this is the start of eight weeks of misery.
Weed Ragweed peaks. Mid-September is typically the highest ragweed pollen day of the year across the Eastern US. Cool nights and warm days accelerate release. Other weeds — mugwort, pigweed, lamb's quarters, sagebrush in the West — are also active. This is a very bad month for the 1 in 5 Americans allergic to weed pollen.
WeedMold Ragweed continues until the first hard frost — mid-October in the North, late October or early November in the South. Mold spikes again as leaves fall and pile up wet. The mold season after leaf fall can rival the spring grass peak for people with mold allergies. First frost brings sudden relief for ragweed sufferers.
Low After the first frost, outdoor pollen drops to near zero in most of the country. Indoor allergens become the dominant trigger — dust mites, pet dander, and mold in damp basements increase as people close windows and spend more time inside. If your symptoms continue through November, indoor allergens or a cold are more likely than outdoor pollen.
Low The quietest month for outdoor allergens in most of North America. The main exception: Texas and the Southwest, where mountain cedar starts releasing before New Year's if temperatures stay mild. Everywhere else, enjoy the break — tree season will resume in 6–10 weeks depending on winter temperatures.
How climate affects your local calendar
The calendar above is a national average. Your local version shifts based on three variables:
Latitude. Every 100 miles north, allergy seasons run roughly one to two weeks later. Atlanta tree season peaks in late March; Chicago peaks in mid-April; Minneapolis peaks in early May. The same offset applies to the fall — ragweed ends earlier in Minnesota than in Tennessee.
Elevation. Mountain communities above 6,000 feet run four to six weeks behind comparable-latitude low-elevation cities. Breckenridge, Colorado has a shorter, later pollen season than Denver, 60 miles east and 4,000 feet lower.
Winter temperature. Mild winters accelerate the following spring's pollen season. If your region had a warm January and February, expect tree pollen to start two to three weeks earlier than the calendar above. The last decade of data shows measurably earlier starts in most of the country — see our guide on how climate change is extending allergy season.
Planning around peak season
A few practical applications of this calendar:
- Outdoor weddings, graduation parties, yard events: Avoid late April through mid-May (tree peak) and September (ragweed peak) if guests include allergy sufferers. Early June and late October are relatively lower-risk windows in most of the country.
- Travel relief: High-altitude destinations (mountains, high desert) and coastal locations with consistent onshore winds tend to have lower pollen counts. Heading to northern Canada or Scandinavia in April? Significantly less oak pollen than at home.
- Prescription timing: Second-generation antihistamines and steroid nasal sprays work best when started one to two weeks before your peak. If March is your worst month, start Flonase in mid-February — not when you're already suffering.
- Yard work scheduling: Mowing, raking, and gardening during your peak season maximizes your exposure. If you can do it in November or February, do it then. If not, wear an N95 mask and shower immediately after.
Regional exceptions worth knowing
Central Texas (Austin, San Antonio, Hill Country): Mountain cedar dominates December through February in one of the most intense allergy seasons in the country. "Cedar fever" is a local colloquialism that understates it — counts can exceed 20,000 grains per cubic meter, roughly 10× what most regions see at tree peak.
Florida and the Gulf Coast: No meaningful dormant season. Some trees and grasses pollinate year-round. Mold is pervasive due to humidity. Total pollen-free days in Miami are very few.
Pacific Northwest (Seattle, Portland): Alder is the dominant early-spring tree and peaks in February and March — earlier than most of the country. Grass season runs later into summer due to mild temperatures. Ragweed is less prevalent than in the East, but mold from wet winters is significant.
Desert Southwest (Phoenix, Tucson, Las Vegas): Olive trees (heavily planted as landscaping) and mulberry are major spring allergens and largely absent in other regions. Monsoon season in July and August spikes mold dramatically.
Sources
- Asthma and Allergy Foundation of America. Allergy Facts and Figures.
- American Academy of Allergy, Asthma & Immunology. AAAAI Pollen Library.
- National Allergy Bureau. NAB certified pollen counting stations.
- Anderegg, W. R. L., et al. (2021). Anthropogenic climate change is worsening North American pollen seasons. PNAS 118(7).
Check today's pollen reading for your area on the home page, or browse the rest of our reference guides.