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Oklahoma Pollen Calendar: Season by Species

Eastern red cedar runs December 15 to March 31. Below: every tracked species, its months, and who published them.

Eastern red cedar pollen typically runs December 15 to March 31 here. In October, the calendar has Grasses, Ragweed in season.
Eastern red cedar season
Dec 15 to Mar 31
In season this October
2
Sourced windows
3

Where the Oklahoma pollen year stands

Climatological windows, resolved against today
Grass + Weed
groups in season, mid October
Grasses, Ragweed
Dec 15 to Mar 31
eastern red cedar season
per Texas A&M AgriLife Today
November 1
median first frost
the date that ends ragweed season here (derived)

The Oklahoma City pollen count station notes a separate fall mountain cedar season, with pollen from the Arbuckle Mountains beginning in mid September, so juniper family pollen can appear in Oklahoma air from fall through early May (Oklahoma Allergy and Asthma Clinic, https://oklahomaallergy.com/educational-materials-pollen-seasons/, fetched 2026-08-27).

The calendar

What pollinates when in Oklahoma

Every bar is a sourced season window; the institution and sentence behind each one are printed in the species cards below. Bars marked ❄ end at Oklahoma’s median first frost, a date we compute from NOAA normals rather than copy from a source, because frost is what physically stops frost-tender weeds like ragweed.

Eastern red cedarTreeDecember 15 to March 31
GrassesGrassMarch 1 to October 31
RagweedWeedAugust 15 to November 1 ❄ derived
trees grasses weeds today❄ end derived from median first frost

Windows are climatological typicals for Oklahoma as published by the sources on this page. They say when a season normally runs, not how strong any given day is.

Ashe juniper foliage densely covered in amber pollen cones
Juniper pollen cones. In cedar country the heaviest tree pollen of the year arrives in winter, which is why a calendar beats a spring-only rule of thumb. “Juniperus ashei pollencones” by micklpickl at Flickr, CC BY-SA 2.0
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Species by species

The windows, with their sources

Each card shows the months, the institution that published them, and the verbatim sentence the window came from. Where a date is computed by us rather than published, the card says so in as many words.

Eastern red cedarTree

Juniperus virginiana

December 15 to March 31

The source puts the peak around January 15.

“These trees typically begin producing pollen in mid-December, often triggered by colder weather or the passage of a cold front. Pollen production peaks in mid-January before slowly tapering off toward the beginning of March. In more eastern parts of the state, eastern red cedars pollinate around the same time and can induce a similar response from people's autoimmune systems.”

Texas A&M AgriLife Today

Neighboring-state source: published by Texas A&M for Texas; the quote itself states eastern red cedars pollinate on the same winter schedule, and the species blankets central and western Oklahoma. OSU Extension redcedar pages could not be cited because extension.okstate.edu blocks automated fetching (HTTP 403). USDA NRCS gives the range wide flowering as "Juniperus virginiana flowers from March to May." (NRCS Plant Guide, https://plants.sc.egov.usda.gov/DocumentLibrary/plantguide/pdf/pg_juvi.pdf, fetched 2026-08-27), supporting an early spring tail; end mapped to Mar 31.

GrassesGrass

Poaceae (bermudagrass, johnsongrass; cool season grasses earlier)

March 1 to October 31 (in season now)

“The warm season grasses such as Bermuda, Bahia, crabgrass, and Johnson begin when the weather becomes warm and do not always stop until a good hard freeze in November.”

Oklahoma Allergy and Asthma Clinic (Pollen Seasons)

FLAGGED private clinic source, used as a last resort because it is Oklahoma specific and OSU Extension pages block automated fetching; the clinic runs the Oklahoma City pollen count. Window is the combined grass envelope: the same page says cool season grasses "can begin as early as late February or March but after a month or two they stop", and warm season grasses run until the November freeze; mapped Mar 1 through Oct 31.

RagweedWeed

Ambrosia spp. (incl. western ragweed)

August 15 to November 1 ❄ end derived from median first frost (in season now)

“almost always begin when the days shorten around the middle of August”

Oklahoma Allergy and Asthma Clinic (Pollen Seasons) · end date computed by us from NOAA 1991 to 2020 frost normals, not published by the source

FLAGGED private clinic source, used as a last resort because it is Oklahoma specific (see grasses entry). The quote is about Oklahoma fall weeds, of which ragweed is the leading member; the same page says the weeds "often continue to pollinate until there is a hard freeze, often in late November". Season end computed from first frost. K-State Research and Extension in adjacent Kansas confirms ragweed as the late summer hay fever culprit: "If you have been suffering from hay fever this fall, a common weed is your culprit rather than the often-blamed goldenrod." (https://www.butler.k-state.edu/horticulture/agent-articles/weeds/common-ragweed/, fetched 2026-08-27).

What the allergy bodies say, in their words. AAAAI: “Seasonal allergic rhinitis is often caused by tree pollen in the early spring. During the late spring and early summer, grass pollen often cause symptoms. Late summer and fall hay fever is caused by weed pollen.” ACAAI: “Tree pollination begins earliest in the year followed by grass pollination later in the spring and summer and ragweed in the late summer and fall.” For anything about symptoms or treatment, see a clinician.

The frost connection

Why ragweed season in Oklahoma ends on a frost date

Ragweed is a short-day annual: it starts shedding pollen as days shorten in late summer and keeps going until cold kills it. The US EPA’s technical documentation for its ragweed pollen indicator puts it plainly: the season “ends in response to cold weather in the fall (i.e., first frost)”, and ragweed “will not continue flowering once temperatures dip below freezing.” EPA’s own analysis truncates every station’s ragweed season at the first fall frost.

This page derives the end date from that rule: Oklahoma's median first fall frost is November 1 (NOAA 1991 to 2020 normals, the same number our first frost pages publish), and that is the derived end date on the ragweed bar above. It is a median: about half of years frost earlier, half later, and EPA's indicator work shows fall frosts arriving later than they used to across the northern states, which is exactly why ragweed seasons have been getting longer.

Common ragweed flower spike held upright against a clear blue sky
Common ragweed in flower. Each spike sheds wind-borne pollen from late summer until the plant is killed by freezing temperatures, which is why the end of its season is a frost statistic rather than a botany fact. “Ambrosia artemisiifolia flowerhead7” by Harry Rose, CC BY 2.0
Live proxy · USA-NPN

Is tree season running early or late in Oklahoma?

USA-NPN’s Extended Spring Indices measure how early or late spring leaf-out and bloom are running against the 1991 to 2020 normal. The index knows nothing about pollen; it tracks cloned lilacs and honeysuckles. But wind-pollinated trees flower in the same early-spring window it measures, so it is a usable, clearly labelled proxy for whether Oklahoma’s tree pollen season is ahead of or behind schedule this year.

First Leaf Index
…
Leaf-out of lilacs and honeysuckles, the earliest woody plants to break bud.
First Bloom Index
…
Flowering of lilacs and honeysuckles, which USA-NPN associates with blooming of early-spring shrubs and leaf out of deciduous trees.
What this is
A proxy, stated as one. The index tracks lilac and honeysuckle leaf-out and bloom, not pollen. Wind-pollinated trees flower in the same early-spring window, so an early index spring usually means an early tree pollen season. It says nothing about grass or ragweed.

The live grid currently holds the finished spring of 2026, shown as history. Tree windows above are not shifted by it; readings for the coming spring start filling in from late January.

Pine branch with yellow pollen cones releasing a visible cloud of pollen into the wind
A pine shedding pollen into the wind. Wind-pollinated trees release enormous quantities because almost none of it lands on another flower, which is also why it lands on everything else. “Pine releasing pollen into the wind in Tuntorp 1” by W.carter, CC BY-SA 4.0
How this page is built

A calendar, not a count

Sourced windows

Every season window names the extension service, agency or university that published it, with the sentence quoted on the card. Where nobody publishes a window, the page says so instead of inventing one.

Derived ragweed ends

Weed bars marked with the frost symbol end on the state’s median first frost, computed from NOAA 1991 to 2020 normals and labelled as derived, on the strength of EPA’s ragweed indicator documentation.

A labelled proxy, not a forecast

The Spring Index anomaly is a measurement of the spring that has already run. It shifts nothing except spring tree windows, and only while the year’s spring is actually in progress.

No counts, by design

Daily counts belong to the certified counting stations of the National Allergy Bureau, and search engines already print them. This site publishes the part nobody prints: the calendar.

Common questions

Oklahoma pollen season FAQ

Orchard grass flower heads with pink anthers spread for wind pollination
Orchard grass in flower, anthers out. Grass pollen is the midsummer act of the calendar almost everywhere, and a lawn kept mowed never reaches this stage, which is the whole connection to the mowing schedule. “Dactylis glomerata - Pink with pollen” by Bob Harvey, CC BY-SA 2.0
The rest of the Oklahoma calendar

Plan around the Oklahoma seasons

Oklahoma frost datesThe median first frost is the date that ends ragweed season here. Same number, two pages.Oklahoma spring bloomThe same Spring Index that flags an early tree pollen year also moves the wildflower calendar.Oklahoma lawn calendarGrass pollen comes from grass allowed to flower. The mowing calendar is the other half of that story.

More Southwest pollen calendars

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Season windows are climatological typicals, each attributed on its card to the institution that published it, with the supporting sentence quoted. Frost-derived weed season ends are computed by us from NOAA 1991 to 2020 median first frost dates and labelled as derived wherever they appear; the frost link is documented by the US EPA’s ragweed pollen indicator technical documentation. Spring Index anomalies are read live in your browser from the USA National Phenology Network (www.usanpn.org, CC BY 4.0) and shown as a labelled proxy for spring tree pollen timing. National picture: every state’s pollen calendar →
Hero image: “Juniperus ashei pollencones” by micklpickl at Flickr, CC BY-SA 2.0