Pollen Calendar 2026: What Pollinates When

There are three seasons, not one, and the American College of Allergy, Asthma and Immunology states the order plainly: "Tree pollination begins earliest in the year followed by grass pollination later in the spring and summer and ragweed in the late summer and fall." Where you live decides the months: in the ACAAI's words, "In many areas of the United States, spring allergies begin in February and last until the early summer", while central Texas gets its heaviest tree pollen in winter and the Gulf states barely get a break at all. Each state page on this site carries its own calendar.

At the first fall frost, which is a different date in every state and a genuinely computable one. The US EPA's technical documentation for its ragweed pollen indicator states that the season "ends in response to cold weather in the fall (i.e., first frost)" and that ragweed "will not continue flowering once temperatures dip below freezing". The table on this page derives every state's ragweed end from its median first frost in the NOAA 1991 to 2020 normals, and labels the result as derived.

Texas A&M AgriLife describes it as "an allergic reaction to the pollen released by mountain cedar trees", which in Texas means Ashe juniper. Their timing: "These trees typically begin producing pollen in mid-December, often triggered by colder weather or the passage of a cold front. Pollen production peaks in mid-January before slowly tapering off toward the beginning of March." It is the reason the Texas and Oklahoma calendars open with a winter tree season the rest of the country does not have.

Certified daily counts come from the National Allergy Bureau stations that produce them, at pollen.aaaai.org, linked from every page here, and search engines print a daily pollen card for most locations. What no count answers is the calendar: which species, which months, in which state, and what date frost shuts the weeds down. That is what these pages publish, with a named source on every window.

The windows are climatological typicals and stay put; the year moves around them. ACAAI notes that "Mild winter temperatures can cause plants to pollinate early." The lower 48 state pages therefore show USA-NPN's Spring Index anomaly as a labelled proxy for whether spring tree season is running early or late, and the ragweed ends are tied to frost rather than to a calendar date. EPA's indicator work found ragweed seasons lengthening most in the northern states as first frosts arrive later.

The ones where winter never quite closes the year: the Gulf Coast, where tree seasons start in January, and the Southwest, where juniper pollen can run from fall right through spring before the grasses even start. The shortest calendars belong to the far north: Alaska compresses trees, grasses and weeds into about four months, per the state epidemiology bulletin quoted on its page.

Barely, and that is what its page shows. National Jewish Health puts it plainly: "Southern states have grass pollens 10 to 11 months out of the year, and Hawaii has grass pollen year-round." The Hawaii calendar bar for grasses runs January through December, kiawe flowers mainly in spring and summer per USDA's Hawaii forestry handbook, and there is no first frost, so nothing on the islands gets a derived weed season end.