Hickory Pollen: The Pecan Family's Other Spring Pollen
Hickory pollen is one of spring's quiet heavyweights. It rarely gets top billing — oak owns the headlines in April — yet across the Southeast and Midwest, hickories are among the most abundant forest trees in the landscape, and when their catkins open, they release pollen in serious volume for several weeks. Hickory also carries a distinction most allergy readers never hear: it is a close botanical relative of the pecan, in the same genus, and the two trees flower on a similar spring schedule, which makes hickory season and pecan season near-mirror images of each other.
Key takeaways
- Hickory pollen comes from trees in the genus Carya — the same genus as pecan — and hickories rank among the most common hardwood trees of the eastern United States, per USDA Forest Service species profiles.
- The AAAAI National Allergy Bureau counts hickory among the tree pollens tracked at stations across the Southeast and Midwest during the spring season.
- Hickory flowering generally runs from April into May, later in the North and earlier in the South, overlapping the oak crest in most regions.
- Pollen Atlas data shows hickory as a recurring top contributor to the Tree Index in southern and midwestern cities during the April crest.
Meet the hickories
Hickories are members of the walnut family, Juglandaceae, and the genus Carya includes roughly a dozen species native to North America. Two of the best known are easy to recognize. Shagbark hickory wears long plates of bark that peel away from the trunk at both ends, giving the tree its shaggy outline. Mockernut hickory, named for its thick-shelled nuts, is one of the most widespread hickories of the Southeast and the Ohio Valley. Pignut, bitternut, and water hickory fill in the rest of the range, from bottomlands to dry ridges.
A family tree with famous relatives
The family connections matter for pollen. Pecan is Carya illinoinensis — a hickory by genus, whatever the grocery aisle calls it — and walnuts are close cousins in the same family. Botanists group these trees together because they share flower structure and pollen characteristics, and the Asthma and Allergy Foundation of America counts the walnut family among the tree groups that contribute meaningfully to spring pollen loads. Our companion guide to pecan pollen covers the cultivated southern member of the family in full.
When hickory pollen flies
Hickories flower in spring, as the leaves emerge. Male flowers form in dangling catkins — slim, greenish tassels that hang in clusters — and release pollen to the wind over a window that typically runs two to four weeks for a stand of trees. The USDA Forest Service species profiles for Carya describe flowering in April and May across most of the range, sliding earlier in the Deep South and later toward the Great Lakes.
| Region | Typical hickory flowering | Season character |
|---|---|---|
| Deep South (Gulf states) | Late March–April | Early, overlaps pecan orchards' bloom |
| Southeast and Ohio Valley | April–early May | Core of the season; overlaps oak crest |
| Midwest | April–May | Strong in river-valley forests |
| Northern edge (Great Lakes, New England) | May | Shorter, later, lighter |
In Memphis, the Mississippi River bottomlands and the wooded bluffs around the city hold dense hickory stands, and April readings there regularly blend hickory with oak. In Atlanta, Piedmont oak-hickory forest is the region's signature woodland type — the two trees literally grow up together — so the April crest is a shared production. Further west, Dallas sits at the meeting point of hickory's range and pecan country, where wild hickories and planted pecans flower within weeks of each other.
Why the overlap matters
Because hickory flowers inside the broader tree pollen season, its pollen rarely acts alone. A high Tree Index day in April in the Ohio Valley is usually a blend — oak first, hickory close behind, with ash, walnut, and maple in supporting roles. The per-plant detail matters precisely because the headline number hides which tree is driving a given day.
How hickory pollen behaves
Built for the wind
Hickory pollen grains are built for wind dispersal: produced in volume, released from elevated catkins into spring air, and carried well beyond the woodland edge that made them. The AAAAI's National Allergy Bureau counts Carya pollen at stations across the East and Midwest, and its seasonal records show the pattern clearly — a build through early spring, a crest that tracks oak closely, and a fade as May hands the season to grasses.
Weather modulates the daily numbers in the usual spring pattern. Warm, dry, breezy days in the flowering window produce the spikes. Rain interrupts release and washes the air, but a stand of hickories flowers for weeks, so the season resumes as soon as conditions dry. Elevation and latitude stretch or compress the window: a mountainside stand can flower a week behind the valley floor below it.
Tracking hickory on Pollen Atlas
On Pollen Atlas, hickory is tracked within the daily Tree Index — scored 0 to 100, Low from 0 to 33, Moderate from 34 to 66, and High from 67 to 100 — with per-plant detail on each city page showing when hickory itself is driving the reading. During April, compare your city against the region on the national city rankings: the hickory-oak crest moves north week by week, and the rankings make that migration visible.
Readers who suspect hickory is one of their triggers can browse the Find an Allergist directory to see who practises nearby. The information here is general and is not medical advice.
Frequently Asked Questions
When is hickory pollen season?
Hickory pollen season runs in spring, generally April into May across most of its range. The Deep South can start in late March, while the northern edge of the range, around the Great Lakes and New England, flowers mainly in May.
Is hickory pollen related to pecan pollen?
Yes — hickory and pecan are in the same genus, Carya, and pecan's scientific name is Carya illinoinensis. The two trees share flower structure and a similar spring flowering schedule, which is why their pollen seasons overlap so closely in the South.
Where is hickory pollen worst?
Hickory pollen is strongest where hickories are most abundant: the oak-hickory forests of the Southeast, the Ohio Valley, and the Midwest's river valleys. Cities ringed by those woodlands, such as Memphis and Atlanta, regularly record hickory among their top spring tree pollens.
How is hickory pollen counted?
Hickory pollen is counted in grains per cubic metre of air by certified counting stations in the AAAAI National Allergy Bureau network. On Pollen Atlas, it appears within the daily Tree Index, with per-plant detail showing hickory's own contribution.
Conclusion
Hickory pollen is the spring season's understudy that turns out to be on stage every night: an abundant eastern hardwood, a close relative of pecan and walnut, and a steady contributor to the April crest from the Gulf to the Great Lakes. Learn its window and its family, and a good part of the spring Tree Index starts to make sense. Your city's count today and its 5-day outlook are free at PollenAtlas.com — worth a look before you make plans
Sources: USDA Forest Service, species profiles for Carya (shagbark, mockernut, and related hickories); American Academy of Allergy, Asthma & Immunology, National Allergy Bureau counting-station network; Asthma and Allergy Foundation of America, pollen allergy education material; Pollen Atlas city index data for Memphis, Dallas, and Atlanta.