Oklahoma Allergy Season: Month-by-Month Pollen Guide

Oklahoma allergy season is less a single season than a relay race. Just as one pollen source fades, another takes the baton, which is why many Oklahomans feel like their symptoms barely get a month off all year. Trees open the year in late winter, grasses carry the middle, ragweed owns the fall, and even winter brings a cedar influence up from the south.

Key takeaways

• Oklahoma allergy season is a relay: trees from February to May, grasses from May to August, ragweed from August to the first frost, and a mountain cedar influence in southern Oklahoma in winter.
• Pollen Atlas data shows Tulsa regularly topping the fall rankings when ragweed peaks, with Oklahoma City and Wichita often climbing the same rankings in the same weeks.
• The ACAAI notes that a single ragweed plant can produce up to a billion grains of pollen in a season — grains light enough to travel hundreds of miles on the wind.
• On Pollen Atlas, each allergen group is scored 0 to 100 — Low 0 to 33, Moderate 34 to 66, and High 67 to 100.

The Oklahoma allergy season calendar, season by season

Here is the shape of the year at a glance. Exact start and end dates shift with the weather in any given year, but the sequence itself is remarkably consistent across the state.

The American College of Allergy, Asthma & Immunology (ACAAI, 2024) describes this same hand-off pattern nationally — trees first, then grasses, then ragweed — but Oklahoma runs the sequence with very little breathing room between acts. A warm February can start trees early, a hot June extends grass, and a late first frost stretches ragweed well into the fall. The calendar below is therefore a planning tool, not a promise: your daily number always outranks the month on the wall.

Spring: tree pollen opens the Oklahoma allergy season

Tree pollen is the opening act, typically building from February and running through May. Oklahoma's wind-pollinated trees — oaks are the heavyweight, alongside elm, ash, pecan, and juniper family trees in different parts of the state — release enormous quantities of fine pollen designed to travel on the breeze. Because the trees leaf out and flower before most people are thinking about allergies, the first itchy eyes of the year often get blamed on a late winter cold.

The March and April spring peak

The spring peak usually lands in March and April, when several tree species overlap at once. On Pollen Atlas, this is when the Tree Index does its annual climb: the index runs from 0 to 100, with Low from 0 to 33, Moderate from 34 to 66, and High from 67 to 100. A run of warm, dry, windy days in March can push readings into the High band for days at a time, while a cold snap or a good rain temporarily knocks them back down. If you track Tulsa pollen readings through the spring, you can watch that sawtooth pattern — sharp rises on breezy afternoons, brief dips after rain — play out week after week.

A season that starts in the south

Northern and southern Oklahoma do not start on the same day. Trees in the southern counties, closer to the Red River, generally begin releasing pollen ahead of trees around Tulsa and further north, sometimes by a couple of weeks in a warm year. That northward creep is your first hint that the state's season is a travelling wave rather than a single switch being flipped.

Summer: grass takes the baton

As tree pollen fades in May, grass pollen takes over and carries the state through to August. Oklahoma summers are built for grass: long hot days, pasture and prairie across much of the state, and lawns and roadsides that keep growing — and keep getting mowed — all season long. Bermuda grass and other warm-season grasses are the main contributors in the southern plains, and they pollinate across a broad summer window rather than in one short burst.

Persistence, not a single spike

Grass season rarely produces the single dramatic spike that ragweed does. Instead it produces persistence: week after week of Moderate readings, punctuated by High days when heat and wind line up. Mowing is a real local factor, too. A freshly cut field, park, or roadside throws pollen and plant fragments into the air at ground level, exactly where people are walking, training, and working outdoors. The American Academy of Allergy, Asthma & Immunology (AAAAI, 2023) notes that grass pollen levels tend to be highest on warm, dry, windy days and lower during and just after rain — a pattern Oklahoma summers, with their pop-up storms followed by hot dry stretches, demonstrate constantly.

Fall: ragweed runs the sharpest stretch

If one part of the year defines Oklahoma allergy season, it is ragweed season, running from August until the first frost. Ragweed is a short-day plant: as daylight shrinks after midsummer, the plants flower and begin releasing pollen, usually from mid-August in Oklahoma, building to a peak in September. The Asthma and Allergy Foundation of America (AAFA, 2024) identifies ragweed as the leading trigger of fall allergy symptoms nationally in its ragweed pollen allergy page, and the ACAAI (2024) notes in its ragweed allergy guide that a single ragweed plant can produce up to a billion grains of pollen in a season — grains light enough to travel hundreds of miles on the wind.

Why the plains suffer so much in fall

That travel is why the plains suffer so much. Oklahoma's open country offers pollen an unobstructed runway, and on a dry, breezy September day a meaningful share of what you breathe may have started its journey in a field counties away. Pollen Atlas data shows Tulsa regularly topping the fall rankings when ragweed peaks, a pattern that repeats across the southern plains — Oklahoma City and, just over the state line, Wichita, Kansas often climb the same rankings in the same weeks. For the full national picture of this season, see our dedicated guide to ragweed season.

Frost ends the ragweed season

The end, at least, is decisive: ragweed plants cannot survive a hard frost, so the season stops when freezing weather arrives — typically October in northern Oklahoma and later further south. Until then, the daily Weeds Index is the number to watch.

Winter: the mountain cedar footnote

Winter is the quietest stretch, but it is not entirely pollen-free, especially in the south of the state. Mountain cedar — Ashe juniper — pollinates in midwinter, roughly December through February, across central Texas, and its pollen travels. Southern Oklahoma counties can catch the northern edge of that season on southerly winds, producing itchy, watery symptoms in the middle of what should be the off-season. The effect is strongest near the Texas border and fades as you move north, but it explains why some southern Oklahomans never quite get a clean break. Oklahoma State University Extension research on eastern redcedar and Ashe juniper documents how spreading juniper populations have increased pollen levels across the state. Our guide to Texas allergy season covers the cedar season in full, since the same air mass links the two states.

For most of Oklahoma, though, December and January are the closest thing to a rest the year offers — a good window to note which season hit you hardest, while the pattern is fresh in your mind.

Reading your Oklahoma pollen count

A calendar tells you which pollen should be around; a daily count tells you what is actually in the air. The AAAAI's explanation of what pollen counts measure draws the same line between measured counts and forecasts, and describes the National Allergy Bureau counting network behind many U.S. measurements. Pollen Atlas scores each allergen group on a 0 to 100 scale — the Total Pollen Index plus separate Tree, Grass, and Weeds indexes, each banded Low (0–33), Moderate (34–66), and High (67–100). In February, the Tree Index is the one that matters; by September, you are watching Weeds. Checking the band, not just the headline number, tells you which of your personal triggers is active today.

Context helps, too. The daily city rankings show whether a rough day in Tulsa is a local spike or part of a regional ragweed wave rolling across the plains — the two call for different levels of concern about tomorrow. And if the same season flattens you year after year, a specialist can help identify exactly which pollens you react to; you can find an allergist near you through the Pollen Atlas directory. This article is general information only and is not medical advice.

Frequently Asked Questions

When is Oklahoma allergy season?

Oklahoma allergy season lasts most of the year, running as a relay from one source to the next. Trees run February to May, grasses May to August, and ragweed August to the first frost, with a winter cedar influence in the south.

When does ragweed peak in Oklahoma?

Ragweed usually begins releasing pollen from mid-August in Oklahoma and builds to a peak in September. The season stops when a hard frost arrives, typically in October in northern Oklahoma and later further south.

Why is Tulsa pollen often high in fall?

Pollen Atlas data shows Tulsa regularly topping the fall rankings when ragweed peaks. Oklahoma's open country lets light ragweed grains travel long distances, so a share of what Tulsa breathes can start counties away.

How can I check the Oklahoma pollen count for my city?

You can check your Oklahoma pollen count on PollenAtlas.com, where the Total, Tree, Grass and Weeds indexes are each scored 0 to 100. In February the Tree Index matters most; by September, watch the Weeds Index.

Conclusion: planning around Oklahoma allergy season

Oklahoma allergy season rewards people who think in seasons rather than days. Trees from February, grass through the summer, ragweed from August to the first frost, and a cedar footnote in the southern winter: once you know which act of the year you are in, the daily numbers start to make sense, and the worst stretches stop arriving as surprises. Wherever in Oklahoma you are, check your city before you plan the week — PollenAtlas.com offers free pollen counts and forecasts for cities in Oklahoma and worldwide, so the season works around you for a change.