Pollen Calendar: When Tree, Grass, Weed, and Mold Seasons Start and End

Two things bend those dates. Latitude and climate move the whole schedule, so the South can start months before the North, which gets a shorter but more compressed season. And the National Allergy Bureau scale means a "High" day is not the same grain count for every pollen, because trees release far more pollen by volume than grass or weeds. Read the calendar below by month to see which allergen is likely driving your symptoms, then check your local count for how heavy it is that day.

Winter: mostly quiet, with two exceptions

For most of the country, January and early February are the low point of the pollen year, because cold air keeps trees dormant and the weeds are long gone. Two exceptions break the calm. In Central Texas and parts of the Southwest, mountain cedar (Ashe juniper) pollinates through the dead of winter, beginning in mid-December and peaking around mid-January, and the reaction it triggers is severe enough to earn the name cedar fever (per Cleveland Clinic). In the mild Southeast, the earliest trees — elm, cedar, and maple — can begin releasing pollen by late February, weeks ahead of the North.

Spring: tree pollen, February through April

Tree pollen is the first major allergen of the year and often the heaviest. Across most of the country it runs from February through April, arriving as early as January in the Deep South and holding off until April or May in the far North. Oak, birch, maple, ash, and juniper do most of the damage. Trees also produce the most pollen by volume, which is why their count thresholds sit so high: on the National Allergy Bureau scale a "High" tree day starts around 90 grains per cubic meter, far above the grass or weed bands (per AAAAI-NAB). A single oak or birch can blanket a neighborhood, so your spring symptoms often track what grows nearby more than what is in your own yard.

Late spring and summer: grass pollen, April into summer

As the trees fade, grass takes over. In northern states the main grasses — Timothy, Kentucky bluegrass, ryegrass, and fescue — pollinate mostly from April through June. In the South, warm-season grasses such as Bermuda and Bahia run far longer, sometimes for much of the year (per AAFA). Grass pollen is more potent per grain than tree pollen, so its scale sits much lower: a "High" grass day begins around 20 grains per cubic meter. That is why a grass count that looks small next to a spring tree number can still flatten a grass-allergic person.

Late summer to fall: weeds and ragweed, August to frost

Weeds close out the pollen year, and ragweed is the one that matters most. It begins releasing pollen in mid-August, peaks in mid-September, and keeps going until the first hard frost, a window of about 6 to 10 weeks in most regions. Day length, not temperature, is the trigger, so ragweed arrives on a dependable late-summer schedule. On the National Allergy Bureau scale a "High" weed day begins around 50 grains per cubic meter. In the South, mild autumns can push the weed season into November, well after northern states have frozen out (per AAFA and EPA).

Mold: July through fall, and it doesn't stop at frost

Outdoor mold is the fourth allergen on the calendar and the one that breaks the pattern. Spore counts climb in warm, humid weather and jump after a rain, and outdoor symptoms tend to run heaviest from July until a hard freeze. What sets mold apart is what comes after: the cold does not kill it. Most spores just go dormant over winter and come back, so a warm, wet autumn can hold mold counts high well past the last ragweed of the year (per AAFA).

How region and a warming climate shift the dates

The calendar above is a national average, and where you live moves it. Mild Southeastern winters pull tree pollen forward and keep outdoor mold active almost year-round. Desert and mountain juniper give the Southwest a tree season that can open in December. Along the Pacific Northwest coast, damp and mild winters bring alder and birch out by February, while the northern Plains and Upper Midwest run a short, intense season packed into a few months. The dates are also drifting: an analysis of dozens of North American monitoring stations found pollen now arrives roughly 20 days sooner and lingers about 8 days later than it did in 1990, with total pollen up around 21 percent (Anderegg 2021, PNAS). Later first frosts are the main reason the fall weed season keeps stretching, especially across the northern states.

How to use the calendar

The point of a pollen calendar is timing. If you know which allergen you react to, start a second-generation antihistamine or an intranasal steroid a week or two before its season opens rather than after symptoms set in, and keep windows shut on warm, dry, breezy days when counts run highest. The calendar tells you which pollen is likely in the air this month; your local daily count tells you how heavy it is right now. If symptoms last for months, or an allergen's season leaves you miserable every year, an allergist can confirm your specific triggers with a skin or blood test (per ACAAI).

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:

• Scranton, PA pollen count — A Northeast valley that runs the full tree-grass-ragweed calendar from February to the first frost.
• Atlanta, GA pollen count — Mild winters open the tree season in February, and oak and pine drive an intense early-spring peak.
• Austin, TX pollen count — Runs a winter mountain-cedar season most of the country never sees, then rolls straight into spring oak.
• Wichita, KS pollen count — Plains grassland stacks a long grass season on top of a heavy late-summer ragweed run.
• Minneapolis, MN pollen count — A short, sharp northern calendar — and the one lengthening fastest as first frosts arrive later.
• New Orleans, LA pollen count — Gulf warmth means little winter pause, so the pollen and mold calendar barely closes.

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
• Allergy Season Calendar: When Each Pollen Peaks by Region
• 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 count by city