If you find yourself asking when allergy season starts every year, the honest answer is: it depends on what you're allergic to and where you live. Allergy season isn't a single window — it's three overlapping seasons (trees, grasses, and weeds), each with its own timing, geography, and dominant offenders. Knowing which one is yours is the difference between guessing and actually getting ahead of your symptoms.
Here's a month-by-month look at allergy season in 2026, what's in the air at each point, and how to time your treatment.
The three allergy seasons
Most people lump everything under "allergy season," but they're really three distinct waves:
- Tree pollen season — late winter through late spring (peaks in April–May in most of the U.S.)
- Grass pollen season — late spring through summer (peaks May–July)
- Weed pollen season — late summer through first hard frost (peaks August–October, dominated by ragweed)
Mold spore counts overlay all three seasons and spike whenever there's been recent rain or warm humid weather.
In milder climates (Florida, southern California, the Gulf Coast), seasons start earlier, end later, and overlap more — many southern allergy sufferers have year-round symptoms.
Month by month: what's in the air
January–February
Mostly quiet in northern climates. In the South, juniper, cedar, and elm trees may already be releasing pollen — "cedar fever" in Texas peaks in December–February and can be intense.
In the rest of the country, indoor allergens (dust mites, mold, pet dander) drive most January–February symptoms. (See Can you get allergies in the winter? for the full picture.)
March
Tree pollen season begins in earnest across most of the U.S. Early offenders include maple, elm, birch, alder, and juniper. New York City typically sees tree pollen begin in March, with levels rising sharply through April.
If you usually struggle in spring, start your daily antihistamine and nasal corticosteroid spray now — these medications work best when you've been on them a week before symptoms arrive.
April
Peak tree pollen month for most of the country. Oak, birch, maple, ash, elm, and cottonwood all flood the air. April 2026 is on track to be one of the most aggressive tree pollen seasons New York has recorded, according to NYC Department of Health data.
Pollen counts are typically highest mid-morning, lower in the evening, and lowest right after a rain.
May
Tree pollen tapers but doesn't disappear. Grass pollen begins — Bermuda, timothy, rye, fescue, Kentucky bluegrass, and Johnson grass. The overlap of tree and grass pollen in May is what makes this month miserable for many allergy sufferers.
June
Grass pollen peaks in most of the country. If your worst weeks are typically late spring through early summer, grass is almost certainly your trigger.
July
Grass pollen continues, often peaking in mid-July before tapering. Mold spores spike during humid summer weeks. Some weed pollens (like English plantain) start to emerge.
August
Grass winds down. Ragweed season begins in late August in northern states, earlier in the South. Ragweed is the single biggest fall allergy trigger — a single plant can release a billion pollen grains, and ragweed pollen has been measured 400+ miles offshore.
September
Peak ragweed month in most of the U.S. Other weed pollens — pigweed, lamb's quarter, tumbleweed, sagebrush — add to the load. September is often the most intense allergy month for those with weed allergies, and asthma flares tend to spike.
October
Weed pollen tapers as cooler weather and shorter days slow plant reproduction. The first hard frost is usually the end of weed pollen season. Mold spores can stay high (raked leaves are mold reservoirs).
November–December
Outdoor pollen mostly ends after the first hard frost. Indoor allergies (dust mites, mold, pet dander) take over. Holiday travel often triggers symptoms from unfamiliar homes, pets, or dusty stored decorations.
How to figure out which season is yours
The strongest clue is timing. Track your symptoms across a calendar for one year: worse in March–May (tree pollen), worse in May–July (grass pollen), worse in August–October (weed pollen, usually ragweed), or worse year-round or indoor-flaring (dust mites, mold, or pet dander).
For confirmation — and a precise list of triggers — an allergist can run skin prick or blood (IgE) tests in about 30 minutes.
Regional variation
When allergy season starts depends a lot on where you live:
- Northeast (NYC, Boston, DC): Tree pollen mid-March through May; grass May–July; ragweed mid-August to first frost.
- Southeast (Atlanta, Charlotte): Tree pollen February through April; grass April–August; weed August–November.
- Midwest (Chicago, Minneapolis): Tree pollen April–May; grass May–July; ragweed mid-August through October.
- Mountain West (Denver, SLC): Shorter, more intense seasons concentrated in spring and early fall.
- Pacific Northwest (Seattle, Portland): Long tree pollen season (February–June) driven by alder and birch.
- Southwest (Phoenix, Vegas): Year-round pollen due to extended growing season.
- Florida and Gulf Coast: Effectively year-round; tree pollen starts in December, grass pollen runs much of the year.
National Allergy Bureau (NAB) certified counting stations publish accurate daily counts at pollen.com and aaaai.org.
When to start (and stop) treatment
The single most useful timing tip: start medications one week before your usual symptom season begins. Antihistamines reach steady state quickly, but nasal corticosteroid sprays take 3–7 days to fully kick in. Starting late means you spend the first two weeks playing catch-up.
Continue medication through your typical symptom window, then stop a week after symptoms resolve. For severe sufferers and those with multiple seasons, year-round nasal corticosteroid use is safe and often recommended.
For a deeper look at treatment, see How to treat seasonal allergies and our complete allergy treatment guide.
Is allergy season getting worse?
Yes, by most measurable indicators. Climate change has lengthened the U.S. allergy season — pollen seasons now start about 20 days earlier and last about 8 days longer than in 1990, and pollen concentrations have risen significantly. Warmer winters mean trees release pollen earlier; longer warm seasons mean ragweed lingers later.
This isn't a reason to despair — modern treatment options are dramatically better than they were a generation ago. But it does mean planning ahead matters more than it used to.
This article is for informational purposes only and is not a substitute for professional medical advice.
Frequently asked questions
When does allergy season start?
Tree pollen typically starts in February (South) or March (most of the U.S.) and runs through May. Grass pollen runs May–July. Weed pollen, especially ragweed, runs August through the first hard frost.
What's the worst month for allergies?
For tree allergies, April or May. For grass, June. For ragweed, September. April and September are usually the two worst months overall for combined allergy sufferers.
How long does allergy season last?
That depends on your trigger and region. Individual pollen seasons run 6–10 weeks; total exposure for someone allergic to all three categories can span 6+ months.
Can rain make allergy season better or worse?
Both. Rain clears pollen out of the air briefly and counts drop the day of and after. But heavy rain can rupture pollen grains and release smaller, more irritating fragments.
Why is allergy season getting longer?
Climate change. Warmer temperatures cause earlier spring blooms and later first frosts. Pollen seasons in the U.S. have lengthened by about 3 weeks since 1990.