Oklahoma Nature Guide: September 2026
Data updated: August 2026Sources & method · Corrections
September turns Oklahoma toward fall — the monarch migration streams south across the prairies, hawks ride the thermals, and the tallgrass golds with sunflowers and goldenrod. The brutal heat finally begins to ease.
Week by week in September
September 3–9
- Scissor-tailed Flycatchers gather in their largest pre-migration roosts and begin streaming south.
- The southbound monarch migration builds across the prairies, nectaring on goldenrod and Maximilian sunflower.
- Goldenrod and aster open together, the signature gold-and-purple look of the Oklahoma fall prairie.
- Plant garlic and multiplying onions for next year as tomatoes and peppers set a strong second crop.
September 10–16
- Songbird migration peaks in the eastern woods with waves of warblers, vireos, and thrushes on cool mornings.
- Maximilian sunflower lines roadsides in spires of yellow as New England and aromatic asters peak in purple.
- The Great Square of Pegasus climbs in the east, leading to the naked-eye Andromeda Galaxy from a dark site.
- Winter squash, pumpkins, and freshly dug sweet potatoes join the last heat crops at the markets.
September 17–23
- The monarch migration nears its peak; on clear days after a north wind they stream past in directional flight.
- Common nighthawks drift south in loose evening flights and the first winter sparrows arrive in the brush.
- The autumn equinox brings nights and days into balance and full dark earlier each evening.
- Black walnuts and green ash go yellow and bottomland sumacs flame scarlet as fall color begins.
September 24–30
- Monarch migration peaks across the Cross Timbers and prairies, with cloudless sulphurs drifting through.
- The first big flights of sandhill cranes arrive, bugling over the western and central plains.
- Pecan husks begin to split in the bottomland groves and the first acorns drop, drawing deer and turkey.
- Harvest the renewed fall tomatoes and abundant greens as the cooler nights bring crops back into production.
Birds This Month
September is a month of departures and arrivals in Oklahoma. The Scissor-tailed Flycatchers gather in their largest pre-migration roosts and stream south through the month, most gone by early October — their leaving is the close of the prairie summer. Mississippi kites, orchard orioles, chimney swifts, and nighthawks also pour south, the nighthawks in loose evening flights over the towns.
Songbird migration peaks in the eastern woods, with waves of warblers — yellow, Wilson's, Nashville, American redstart, and many more — plus vireos, thrushes, tanagers, and grosbeaks moving on cool-front mornings. Shorebirds continue at Salt Plains and Hackberry Flat, and the first Franklin's gulls stream across in their famous prairie migration. Broad-winged hawks and other raptors ride south on the thermals.
The earliest winter sparrows and ruby-crowned kinglets arrive late in the month, and the first returning ducks appear on the reservoirs as the season turns.
This month's tip: September rewards watching the sky — gathering scissor-tails and kites by day, nighthawks at dusk, and warbler waves after a cool front. Catch the last great scissor-tail roosts before the state bird leaves for the winter.
What's Blooming
September is the gold-and-purple climax of the Oklahoma prairie year. Maximilian sunflower — the tall, native, late-season giant — lines roadsides and field edges in spires of yellow, joined by sheets of common sunflower, the deep purple of New England and aromatic asters, and a flush of goldenrods. The combination of goldenrod and aster is the signature look of the Oklahoma fall prairie.
The tallgrass prairie blazes with broomweed's yellow, blue sage (pitcher sage), snow-on-the-mountain, and the last blazing star and ironweed, while the big bluestem and Indian grass turn copper and wine-red around them. Eastern seeps still show scarlet cardinal flower, and pastures gild with broomweed and late partridge pea.
Where to see it: the Tallgrass Prairie Preserve is at one of its most beautiful moments, gold with Maximilian sunflower and purple with aster against reddening grass. Roadsides across central and eastern Oklahoma carry the goldenrod-and-aster show, the nectar engine fueling the monarch migration now streaming through.
Garden This Month
September is a rewarding month in the Oklahoma garden as the heat finally breaks and the fall crops surge. The cool-season planting continues at full pace: direct-sow spinach, lettuce, arugula, radishes, turnips, kale, mustard, and carrots early in the month, and transplant broccoli, cabbage, cauliflower, and collards for a fall and early-winter harvest. The summer garden often rallies, too — tomatoes and peppers that sulked in the July heat set a strong second crop as the nights cool.
This is also the prime month to plant garlic and multiplying onions for next year, and to start strawberry beds and cool-season cover crops. Keep the fall seedlings watered through any lingering warm, dry spells, and watch for fall armyworms and grasshoppers, which can strip a young fall planting fast. As the first cool fronts arrive, note your average first-frost date — late October to mid-November across most of the state — and plan to harvest or cover the tender summer crops before it comes. September's mild weather makes it one of the most pleasant working months of the Oklahoma gardening year.
Zone 7a (central and northeastern Oklahoma): the fall garden grows fast as the heat breaks. Keep planting cool-season crops early in the month — spinach, lettuce, radishes, turnips, and greens — set out garlic late in the month, and harvest the fall tomatoes, beans, and squash as they ripen.
Zone 7b (south-central and southeastern Oklahoma): a long, generous fall season lies ahead. Continue sowing greens, roots, and lettuce, transplant broccoli and cabbage, and enjoy a renewed flush of tomatoes and peppers as the cooler nights bring them back into production.
What's at the Farmers Market
September markets straddle summer and fall in Oklahoma. The last of the heat crops — tomatoes, okra, peppers, eggplant, southern peas, and the final melons and sweet corn — share the tables with the first true fall produce: winter squash like butternut and acorn, the first pumpkins, freshly dug sweet potatoes, and cool-season greens returning sweet from the field.
Orchards bring apples, pears, and grapes, and the first new-crop pecans appear by late month from the bottomland groves. Tables fill with onions, garlic, fall beans, and bright autumn cut flowers — sunflowers, dahlias, and celosia. Farm eggs and local honey, freshly extracted from the late-summer flow, remain steady.
For selection and storage: choose winter squash and pumpkins that are firm, fully colored, with a hard dry stem, and cure and store them in a cool, dry, airy spot rather than the refrigerator. Keep sweet potatoes warm and ventilated, not chilled; hold the last tomatoes at room temperature; refrigerate greens and beans crisp and dry; and keep new pecans cold and sealed so the oils stay fresh.
Night Sky This Month
September's cooling, clearing nights and the autumn equinox make for excellent Oklahoma stargazing. The remote Black Mesa country and Black Mesa State Park in the panhandle remain the darkest skies in the state, and the open Wichita Mountains near Lawton give central Oklahoma a fine, accessible dark site; clubs around Tulsa and Oklahoma City run star parties as the crisp post-front air settles in.
The summer sky still dominates early — the Milky Way arches overhead from Sagittarius through the Summer Triangle — but the autumn constellations are rising in the east. The Great Square of Pegasus climbs after dark, leading the chain of stars to Andromeda and the faint smudge of the Andromeda Galaxy, the most distant object visible to the naked eye, beautifully placed from a dark Oklahoma site. The W of Cassiopeia rides high in the northeast.
The autumn equinox brings nights and days into balance and full dark earlier each evening. There is no major meteor shower this month, but the rising Andromeda Galaxy and the still-glorious Milky Way reward binoculars from a dark prairie horizon. For this year's exact equinox timing and planet positions from your Oklahoma latitude, see the printable Oklahoma night-sky guide.
Butterflies & Pollinators
September is the great monarch month in Oklahoma. The state sits squarely in the central flyway, and through September the southbound monarch migration funnels across the prairies and Cross Timbers — peaking in late September into early October — with adults nectaring heavily on goldenrod, aster, and Maximilian sunflower to fuel the journey to the Mexican overwintering forests. On a good day after a cool front, monarchs stream past in a steady directional flight, one of Oklahoma's finest wildlife spectacles.
Other migrants and late broods abound: the queen (the monarch's southern relative), common buckeyes staging a strong southbound push, painted and American ladies, variegated and Gulf fritillaries, sulphurs, and many skippers crowd the fall flowers. Cloudless sulphurs, big and lemon-yellow, drift north and through as a southern migrant.
To make the most of the season: September is the month to witness and support the monarch migration — keep goldenrod, aster, sunflower, and zinnia blooming as fuel stops, and visit a prairie or roadside on a clear day after a north wind to see the monarchs streaming through. Reporting monarch numbers to community-science projects helps track this iconic passage.
What to plant for them is in the Oklahoma native plants guide
Trees This Month
September begins the slow turn of the Oklahoma tree year. The earliest fall color shows in the bottomlands and on stressed trees — the black walnuts and green ash go yellow, the sumacs flame scarlet along fencerows and woodland edges, and the cottonwoods along the rivers begin dropping yellowing leaves. The persimmons in the southeast ripen their fruit to soft orange.
The nut harvest is the season's main event. The pecans — a signature Oklahoma crop — finish filling, and their husks begin to split late in the month in the river-bottom groves; the oaks drop the first acorns, drawing deer, turkey, and squirrels; and the black walnuts let go their green husks. The eastern red cedars are heavy with ripening blue cones. The Cross Timbers post oaks and blackjack oaks still hold their summer green, among the last to turn, while the eastern hills begin to show the first patches of yellow and red that will spread into October's full color.
The Oklahoma native plants guide covers what grows with them
Weather & Daylight
Across Oklahoma, a typical September day averages a high near 85°F and a low near 61°F, with about 3.3 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
Heat finally breaks toward the mid-80s, nights cooling into the 60s, though rain stays steady through the shift.
| Average high | 85°F |
|---|---|
| Average low | 61°F |
| Precipitation | 3.3 in |
| Sunrise (mid-month) | 7:10 CT |
| Sunset (mid-month) | 19:36 CT |
Figures are statewide averages over the 1991–2020 U.S. climate normals; local conditions vary with elevation and distance from the coast. Sunrise and sunset are computed for a midstate point on the 15th (CT).
Next month's version of this page, by email
One short note when Oklahoma's next month turns — what's arriving, blooming, and worth a night outside.
Go deeper with the Oklahoma guides
The complete Oklahoma birding, native-plant, and night-sky references — or the whole year, week by week, in one book.
Same month elsewhere: September in Oregon · September in Pennsylvania · September in Rhode Island