US Pollen Calendar 2026: Allergy Seasons Month by Month

📅 September at a glance

It's September, and common ragweed, giant ragweed, lamb's quarters and Russian thistle (West) are usually at their peak in the US. Another 2 types are still in the air too, including grass (overall) and Bermuda grass.

These windows are what a typical year looks like; the weather nudges them earlier or later. For what's actually in the air today, check the live pollen count for New York or find your city.

Trees

Tree season opens the year twice. Mountain cedar gives central Texas its winter 'cedar fever' from November through February. The national spring wave follows: elm and maple from February, then oak, the heaviest-volume US tree pollen, from late winter in the South through June in the North, with birch, ash and mulberry in between.

Grasses

Grass season splits by climate. Northern cool-season grasses (timothy, bluegrass, orchard grass) peak May through July; southern warm-season Bermuda grass starts around April and runs into October. On the Gulf Coast grass pollen can linger at low levels nearly year-round.

Species	Apr	May	Jun	Jul	Aug	Sep	Oct
Grass (overall)	in season	peak	peak	peak	in season	in season
Timothy grass		in season	peak	peak	in season
Bermuda grass	in season	in season	peak	peak	peak	in season	in season

Weeds

Fall belongs to ragweed, the cause of roughly three-quarters of US fall hay fever. It starts in mid-August, peaks in mid-September and lasts until the first hard frost. Out West, Russian thistle (tumbleweed) and lamb's quarters drive the summer weed load.

In season Peak Current month

When does pollen season start and end in the US?

Across most of the country the pollen year runs as three waves: trees from late winter (February to March) through June, grasses from April into September, and weeds, above all ragweed, from mid-August until the first hard frost in October or November. Central Texas adds a fourth, upside-down season: mountain cedar (Ashe juniper) sheds from November through February, peaking around the turn of the year, the notorious ‘cedar fever’. The US is continent-sized, so treat these windows as a national envelope. The Deep South and Gulf Coast run roughly four to six weeks earlier (tree season can start in January, and ragweed can outlast November), the northern tier compresses toward the middle months, and the desert Southwest has its own early spring driven by mulberry and olive. For what’s actually in the air today, check the live pollen count for New York or find your city.

What about pecan, juniper in the East, and the yellow pine dust?

A few famous American allergens aren’t separate rows here. Pecan and hickory are top-tier spring tree allergens across the South and lower Midwest in April and May, but aren’t yet tracked individually by our model. Eastern red cedar, the juniper most Americans outside Texas actually meet, sheds in late winter and spring (roughly February to April in the East); the mountain-cedar row above describes the Texas winter species only. Kentucky bluegrass, Johnson grass and Bahia grass are covered within the overall grass row. The yellow pine dust that coats the South every April is the most visible pollen in America but only weakly allergenic; oak, birch and grasses flying at the same time cause most of the symptoms it gets blamed for. Texas also gets a fall elm season (cedar elm, August to October) that the spring elm row doesn’t cover. Where a row uses one species for a wider group (oak, elm, ash, maple), the window shown is for the group.

Frequently asked questions

When does ragweed season end?

Ragweed season in the US starts in mid-August, peaks in mid-September, and ends with the first hard frost: mid-to-late October in the North, lingering into November in the South.

When is cedar fever season in Texas?

Mountain cedar (Ashe juniper) sheds from roughly mid-November through February in central Texas, peaking from December into mid-January. It's the one major US pollen season that happens in winter.

When does tree pollen season start in the US?

In the South, tree pollen (elm, maple, early oak) can start in January–February; across most of the country the main tree wave runs March through May, with oak peaking in April–May and stretching into June in northern states.

Species	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Common ragweed
Giant ragweed
Lamb's quarters
Russian thistle (West)