April Allergies: The Month the Tree Pollen Crest Arrives
April allergies are the main event of the US pollen year. March opens the season in the South, and May hands the stage to grasses in much of the country, but April is when the tree pollen crest rolls across the largest share of the population at once — the Southeast at full strength, the mid-Atlantic and Midwest climbing to their peaks, and the Northeast and Upper Midwest opening their seasons as the South begins to ease. If one month explains why spring has its reputation, it is this one.
Key takeaways
- April is the peak tree-pollen month for much of the United States, according to the seasonal patterns tracked by the AAAAI National Allergy Bureau's counting-station network.
- The Asthma and Allergy Foundation of America (AAFA) identifies tree pollen as the first and one of the most potent waves of the spring allergy season.
- The April crest moves north week by week: the Gulf Coast and Southeast crest first, the mid-Atlantic and Midwest follow mid-month, and the Northeast crests last.
- Pollen Atlas data shows April producing the year's highest Tree Index readings in more US cities than any other month.
Why april allergies crest in April
April's dominance is a matter of overlap. By April, the southern tree season — which opened in February and March — is at full strength, while the northern tree season is switching on. For a few weeks, both run at once. The American College of Allergy, Asthma and Immunology notes that tree pollen is the leading spring allergen in most of the country, and April is when the largest number of tree species, in the largest number of places, are flowering simultaneously.
The cast of April trees
The month has a recognizable cast. Oaks are the heavyweights across the East, South, and Midwest — whole genera flowering within the same few weeks. Alongside them: hickory and pecan in the South, ash and walnut through the interior, maple and elm early in the month, birch building toward the northern crest late in the month, and juniper and cedar finishing their long western and Texas runs. In Atlanta, April is famous for the yellow-green film that settles on every outdoor surface — a visible marker of just how much tree pollen the air is carrying. Our full tree pollen season guide walks the whole spring sequence from first maple to last birch.
April allergies, week by week
The crest is a moving wave, and a week-by-week read shows it traveling:
| April week | South and Gulf Coast | Mid-Atlantic and Midwest | Northeast and Upper Midwest |
|---|---|---|---|
| Week 1 | At or near crest (oak, hickory) | Climbing fast; maple, elm, early oak | Season opening in mild years |
| Week 2 | Crest continues; grasses start | Crest arrives for many metros | Climbing; maple and ash |
| Week 3 | Tree counts easing; grass building | Crest, then first easing late | Approaching crest; birch starts |
| Week 4 | Grass season taking over | Grass handoff begins | Crest (oak, birch) |
The southern crest comes first
In Dallas and across the Gulf states, the first half of April is the summit of the tree year — post oak and other oaks, pecan, and ash overlapping — and by late April the baton passes to grasses. Southern readers often feel April as two seasons in one month.
The northern crest closes the month
In New York and the Great Lakes cities, April is a ramp rather than a summit: maples and elms early, oaks mid-month, birch gathering strength toward May. Northern April counts can swing wildly with the weather, because a single warm week can pull the whole sequence forward.
Weather writes April's daily story
The AAAAI National Allergy Bureau counts pollen in grains per cubic metre, and April counts at those stations swing with a familiar set of levers. Warm, dry, breezy days produce the spikes, as trees release into moving air that keeps grains aloft. Rain scrubs the air for a day or two — then, as AAFA's pollen education material describes, counts commonly rebound quickly once surfaces dry, because the trees are still flowering and the next release is already staged. A late cold snap can pause flowering and compress the remaining season into fewer, stronger days when warmth returns.
After April: the handoff
One more feature of the month deserves noting: April is when pollen becomes visible to everyone, not just to counting stations. The yellow-green film on cars and porches across the South and mid-Atlantic, the catkins collecting in gutters, the dust rinsed off sidewalks by spring rain — all of it peaks in April, because April is when the largest number of wind-pollinated trees are releasing at once. That visibility is part of why the month anchors the public idea of allergy season, even in northern cities where May's grass-and-birch combination can rival it in the counts.
April does not end the spring; it hands it off. Grasses take the lead in May across most of the country, and the June pollen picture is a grass picture with the last northern trees finishing at its edges. On Pollen Atlas, the handoff is easy to watch: the Tree Index eases down the rankings while the Grass Index climbs, city by city, on the national city rankings.
During April itself, the most useful habit is a daily one — the crest is not a single day but a run of days, and the per-plant detail on each Pollen Atlas city page shows whether oak, birch, or another tree is driving your reading. Anyone wondering which April pollens affect them personally can look through the Find an Allergist directory, which Pollen Atlas maintains as a reference. This article is general information only and is not medical advice.
Frequently Asked Questions
What pollen is out in April?
Tree pollen dominates in April, led by oak across much of the East, South, and Midwest. Hickory, pecan, ash, walnut, maple, and elm also flower during the month, birch builds in the North, and grasses begin in the South by late April.
Why are allergies so bad in April?
Allergies are bad in April because the southern and northern tree seasons overlap. The South is at its crest while the North is switching on, so more tree species are flowering in more places at the same time than in any other spring month.
When in April is pollen highest?
Pollen is highest in April on different dates by region: the first half of the month in the South, mid-April across the mid-Atlantic and Midwest, and late April in the Northeast and Upper Midwest. Warm, dry, windy days produce the sharpest individual spikes within those windows.
Do April allergies end in May?
April allergies ease in May for southern readers as trees finish and grasses take over. Northern readers may find May just as strong, because their tree crest arrives later and grass season overlaps it.
Conclusion
April allergies are the crest of the American pollen year — a northward-moving wave of oak, hickory, birch, and a dozen other trees, peaking in the South as it opens in the North. Know which week of the wave your city is riding, and the month becomes a schedule instead of an ambush. Free counts. Free forecasts. Worldwide. PollenAtlas.com has your day covered
Sources: American Academy of Allergy, Asthma & Immunology, National Allergy Bureau counting-station network and pollen resources; Asthma and Allergy Foundation of America, pollen allergy education material; American College of Allergy, Asthma and Immunology, public pollen education pages; Pollen Atlas city index data for Atlanta, Dallas, and New York.