Tree pollen: oak, birch, maple, and friends

Tree pollen is the opening act — February through May, peaking in April for most of the country. It's the heaviest-hitting season for most allergy sufferers, and it involves dozens of species releasing simultaneously. Here's who the main offenders are, when they run, and how to tell which one is responsible for your particular misery.

The short answer

In North America, the most allergenic trees are oak, birch, cedar/juniper, alder, maple, ash, and elm. Each has a slightly different season window, but they overlap enough that from March through May most allergy sufferers are reacting to a rolling combination rather than a single culprit. Oak is the single biggest offender by volume — one mature tree can release over 100 million pollen grains in a season.

The yellow-green film that coats cars and porch furniture in April? Almost always oak. It's not just visible — it's also highly allergenic. Pine pollen, by contrast, produces the dramatic yellow clouds but is largely hypoallergenic; its grains are too large to reach the lower respiratory tract.

Why trees use wind — and why that's bad for you

About 90% of tree species that cause allergies are wind-pollinated (anemophilous). Wind pollination is evolutionarily cheap: no need to produce nectar, bright colors, or fragrance to attract insects. Instead, trees produce astronomical amounts of tiny, light pollen and let the wind scatter it — hoping a grain lands on another tree of the same species. The collateral damage is your immune system.

Wind-pollinated pollen grains are engineered for travel: 10–40 microns in diameter (small enough to inhale deeply), aerodynamically smooth or structured for lift, and produced in quantities that ensure saturation. Insect-pollinated trees (fruit trees, magnolias) are far less problematic because their pollen is sticky and heavy, designed to cling to bees rather than drift through the air.

This is also why the "hypoallergenic landscaping" advice matters: a neighborhood planted with male ash, male maple, and oak is dramatically worse for allergy sufferers than one with insect-pollinated or female-only specimens of the same species.

The major offenders, one by one

Oak — the biggest volume producer

Season: Late March through May, peaking in April.
Range: Eastern two-thirds of the US; also Southern California live oak.
Allergenicity: Very high.

Oak (Quercus spp.) is arguably the single most consequential allergy tree in North America. A single mature oak drops enough pollen to visibly yellow the ground beneath it. The pollen is small, highly allergenic, and produced so abundantly that it dominates air-quality readings across the entire East Coast during April. The 11 most allergenic oak species are all wind-pollinated, and most suburban and urban tree canopies contain significant oak.

The good news: oak season is relatively predictable. If your worst weeks are the last two of April, oak is the very likely culprit.

Birch — the cross-reactor

Season: Late March through May, peaking mid-April.
Range: Northern US, upper Midwest, Northeast, Pacific Northwest; everywhere with cold winters.
Allergenicity: Very high, with important cross-reactivity.

Birch (Betula spp.) pollen contains a protein called Bet v 1 that cross-reacts with proteins in many raw fruits and vegetables — apples, pears, cherries, peaches, almonds, hazelnuts, carrots, celery. This is oral allergy syndrome (OAS): birch-allergic people often experience tingling or itching in the mouth when eating these foods during pollen season, even if they've eaten the same foods without issue in winter. Cooking usually destroys the cross-reactive protein, which is why the same apple that causes symptoms raw is fine in a pie.

If you're newly noticing mouth tingling when eating fruit in April, and it wasn't there in December, birch pollen cross-reactivity is a likely explanation.

Cedar & juniper — the winter offenders

Season: December through March (Texas: December–February peak).
Range: Central Texas, Oklahoma, Arkansas, Southwest, Pacific Northwest (western red cedar).
Allergenicity: Extremely high in affected regions.

Mountain cedar (Juniperus ashei) is responsible for cedar fever — the phenomenon where central Texans experience debilitating allergy symptoms that mimic the flu in the middle of winter. At peak, cedar counts in the Austin and San Antonio area routinely exceed 10,000–20,000 grains per cubic meter, among the highest pollen readings recorded anywhere in the country. People who move to Texas from low-pollen regions often develop cedar sensitivity within a few seasons.

Elsewhere, Eastern red cedar (J. virginiana) is the main culprit. It's extremely common as a "volunteer" tree in disturbed soils and fence rows throughout the South and Midwest.

Alder — the earliest starter

Season: January through April, depending on region.
Range: Pacific Northwest (dominant), Northeast, upper Midwest.
Allergenicity: High; cross-reacts with birch.

Alder (Alnus spp.) is the first major tree to release pollen in the Pacific Northwest, often starting in late January during mild winters. In Seattle and Portland, alder is the dominant spring allergen — it arrives well before trees like oak or maple are active. Alder and birch belong to the same family (Betulaceae) and share cross-reactive proteins, so if you're sensitized to one, you're likely reactive to the other.

Maple — the overlooked opener

Season: March through April.
Range: Eastern US, upper Midwest; very widespread.
Allergenicity: Moderate to high.

Maple (Acer spp.) is one of the first trees to flower in late winter and early spring, often releasing pollen before its leaves appear. Because maple flowers are small and inconspicuous, many people don't realize their March sneezing is maple-related. Red maple and silver maple are the biggest offenders. Box elder (Acer negundo), technically a maple, is also highly allergenic and extremely common across the Midwest.

Ash & elm — March's quiet contributors

Season: February through April.
Range: Widespread across the Eastern US and Midwest.
Allergenicity: Moderate to high.

Ash (Fraxinus spp.) and elm (Ulmus spp.) release pollen in late February and March, before most trees are active. Elm in particular is one of the earliest-starting trees in the Midwest. Note that white ash has male and female trees — only male trees release pollen — and the widespread loss of ash trees to emerald ash borer has actually reduced ash pollen loads in affected regions.

What does NOT cause allergies (despite appearances)

Pine is the classic example of a visually dramatic but largely harmless pollen. Pine releases clouds of bright yellow powder visible from 50 feet away — and then almost nothing happens to most allergy sufferers. Pine pollen grains are large and buoyant, not optimized for deep inhalation, and the proteins in pine pollen are not particularly reactive in most human immune systems. If your car is coated in yellow but you feel fine, pine is probably the explanation.

Flowering ornamental trees — cherry, apple, magnolia, dogwood, Bradford pear — are insect-pollinated. Their pollen is sticky and heavy, designed to cling to pollinators, not drift through the air. A street lined with blooming cherry trees is beautiful and essentially harmless to allergy sufferers. The birch tree next to it is a problem; the cherry is not.

How to tell which tree is getting you

The most useful diagnostic is timing. Keep a symptom log and match it against local pollen reports (the home page breaks out tree, grass, and weed counts separately). If your symptoms start mid-March and peak the last week of April in the mid-Atlantic, oak is almost certainly the primary driver.

For a definitive answer, a skin-prick test at an allergist's office will tell you exactly which tree proteins your immune system reacts to. A standard panel tests 15–20 tree species individually. Blood tests (specific IgE panels) are an alternative if skin testing isn't available.

Oral allergy syndrome clues are also useful: if eating raw apples, pears, or stone fruits causes mouth tingling during spring but not winter, birch cross-reactivity is very likely even if your main symptom is nasal.

Managing tree pollen exposure

• Start medication early. Steroid nasal sprays like Flonase take 3–5 days of daily use to reach full effect. Start two weeks before your typical symptom onset — not when you're already sneezing.
• Time outdoor activity. Pollen is released in the morning, peaks between 8 AM and noon, and disperses through the afternoon. Exercise outdoors in the late afternoon or after rain.
• Keep windows closed in April. A bedroom window open at 7 AM during oak peak lets in enormous quantities of pollen. HVAC air, filtered, is considerably cleaner.
• Shower and change clothes after outdoor time. Pollen deposits on hair, skin, and clothing — bringing it indoors and onto your pillow.
• HEPA filter in the bedroom. See our guide on HEPA filters for sizing and placement guidance.
• Consider immunotherapy for severe cases. Allergy shots and sublingual tablets (available for birch, grass, and dust mites) can reduce sensitivity over 3–5 years. An allergist can assess whether you're a candidate.

Sources

• American Academy of Allergy, Asthma & Immunology. AAAAI Pollen Library.
• National Allergy Bureau. Certified pollen-counting stations.
• Asthma and Allergy Foundation of America. Pollen allergy overview.
• Ogren, T. L. (2015). The Allergy-Fighting Garden. Ten Speed Press. (Source for OPALS landscaping allergenicity scores.)

Check today's tree pollen reading for your area on the home page, or browse the rest of our reference guides.