September turns Indiana toward fall — the goldenrod and asters at their height, the fall bird migration in full flow, the monarchs streaming south along Lake Michigan, and the first touches of color in the trees. The heat breaks into crisp mornings, and the harvest shifts from summer fruit to apples, pumpkins, and the last of the melons.
Week by week in September
September 3–9
- Broad-winged hawks stream past Indiana Dunes in big kettles as the hawk migration peaks along the lakeshore.
- Goldenrods and asters reach their fall climax, painting every old field and roadside gold and purple.
- Plant garlic and spring bulbs, divide perennials, and seed or overseed cool-season lawns while the soil is still warm.
September 10–16
- The monarch migration funnels along the Lake Michigan shore at Indiana Dunes — hundreds may drift past on a north wind.
- Warblers, vireos, and thrushes pour south through the woods, best seen where Lake Michigan concentrates them at the Dunes.
- Indiana apples come into full season with fresh-pressed cider and the start of pumpkin season.
September 17–23
- The autumn equinox passes and the Harvest Moon rises large and golden in the eastern evening sky.
- Black gum, sumac, and Virginia creeper flame red as fall color begins in earnest across the woods.
- The earliest sandhill cranes return as white-throated and white-crowned sparrows arrive in the brushy edges.
September 24–30
- Bottle gentian deep-blues the wet prairies and the bronzing big bluestem and Indian grass dominate the grassland color.
- The southern hills around Brown County clearly tip toward their famous autumn blaze as walnut and ash drop early.
- Pumpkins and gourds pile up at the stands and the orchards reach their busy fall peak.
Birds This Month
September is a peak month for fall migration in Indiana. The warblers pour south through the woods again — confusing in their drab fall plumage, but in great numbers — best seen at Indiana Dunes National Park, where Lake Michigan concentrates migrants. Along with them move vireos, thrushes, flycatchers, rose-breasted grosbeaks, and scarlet tanagers. The Dunes are also a renowned hawk migration watch site, with broad-winged hawks streaming past in big kettles mid-month, plus sharp-shinned hawks, ospreys, bald eagles, and the first peregrine falcons.
Ruby-throated hummingbirds pass through in good numbers early in the month before departing — keep feeders up for stragglers. Common nighthawks stream over in evening flocks, nighthawk and swift numbers dwindle, and shorebirds continue at Goose Pond. By late September the first sparrows — white-throated, white-crowned, and others — and the earliest sandhill cranes begin to return, the leading edge of the great fall staging that builds at Jasper-Pulaski through autumn.
What's Blooming
September is the climax of Indiana's fall wildflower display, the prairies and roadsides ablaze in gold and purple. Goldenrods of many kinds — tall, Canada, stiff, and showy — dominate every old field and grassland, paired with the purples and whites of the asters: New England aster in deep violet, smooth, heath, and aromatic asters, and the lavender sky-blue aster. At Goose Pond the prairie glows with these plus tall ironweed, sneezeweed, bottle gentian, and the bronzing grasses.
The wet margins hold the last cardinal flower, great blue lobelia, and joe-pye weed, and the woodland edges show the orange of jewelweed still drawing the last hummingbirds. These late bloomers are the critical final nectar source of the year, fueling the southbound monarchs and migrating insects. In gardens, the asters, mums, sedums, dahlias, and Japanese anemones carry the color into fall, and the goldenrod-and-aster combination of the wild edges is the signature look of an Indiana September.
Garden This Month
September is the pivot from harvest to autumn work. The summer garden winds down — the last tomatoes, peppers, beans, and melons ripen before the first frost, which arrives in October — while the fall crops come into their own: broccoli, cabbage, kale, collards, lettuce, spinach, radishes, beets, turnips, and carrots all thrive and sweeten in the cooling weather. Keep harvesting, and watch the forecast for the first frost date so you can pick or cover tender crops in time.
This is a key planting month for next year. Plant garlic toward month's end for a summer harvest, set out spring-flowering bulbs (daffodils, tulips, crocus) as the soil cools, divide and transplant overcrowded perennials, and plant new trees and shrubs while the warm soil and cool air favor root growth. Early-to-mid September is also the prime window to seed or overseed cool-season lawns. Begin a tidy fall cleanup, but leave seed heads and some standing stems for the birds and overwintering insects.
Zone 5b (northern Indiana & the lake region): the first frost can arrive by early-to-mid October, so harvest tender crops before it and keep row cover ready. Plant garlic and spring bulbs late in the month, sow a quick crop of spinach and lettuce, and start fall cleanup.
Zone 6a (central Indiana): the first frost usually comes mid-to-late October. Harvest fall greens and root crops, plant garlic and spring bulbs, divide perennials, and seed or overseed cool-season lawns now while the soil is still warm.
Zone 6b (the southern Ohio River counties): frost may hold off into late October or November, leaving a long, productive fall. Keep harvesting and even sow a last fast crop of greens and radishes; plant garlic and cover crops, and start fall bulb planting late in the month.
What's at the Farmers Market
September markets bridge summer and fall, and the variety is at its widest. The last summer crops linger — tomatoes, peppers, eggplant, sweet corn, melons, okra, and green beans — while the fall harvest arrives in force: winter squash, pumpkins, sweet potatoes, broccoli, cabbage, kale, leeks, and the first fall greens. Indiana apples come into full season, with early and mid-season varieties filling the orchard stands, and the last peaches finish.
This is the start of pumpkin and gourd season, the stands piling up with jack-o'-lantern pumpkins, decorative gourds, and ornamental corn. Concord and other grapes ripen, and the first wild and orchard pears appear. Cut flowers turn to sunflowers, dahlias, and mums. Choose pumpkins and winter squash with hard rinds and dry, intact stems and cure them in a warm spot before storing cool and dry; pick firm, unblemished apples and store them cold for keeping.
Night Sky This Month
September brings the autumn equinox, the return of earlier darkness, and a transition in the sky. The Summer Triangle of Vega, Deneb, and Altair still rides high overhead in the early evening, with the summer Milky Way arching through Cygnus the Swan — still well worth tracing with binoculars from a dark site before it slides west. In the east the autumn constellations climb: the Great Square of Pegasus, the W of Cassiopeia, and the chained figure of Andromeda, which carries the faint smudge of the Andromeda Galaxy — the most distant object visible to the naked eye, easiest to find on these dark fall nights.
There is no major meteor shower in September, so it is a month for the Milky Way, the equinox, and the rising autumn sky. The crisp, drier nights of late September often bring excellent transparency. Watch the eastern evening sky for the Harvest Moon near the equinox, rising large and golden. The printable Indiana night-sky guide gives this year's planet positions and equinox details for your part of the state.
Butterflies & Pollinators
September is the month of the monarch migration in Indiana, the season's great butterfly event. Streams of southbound monarchs move through the state all month, funneling along the Lake Michigan shore at Indiana Dunes, where on a good day with a north wind hundreds drift past, pausing to nectar on goldenrod and aster before continuing toward Mexico. Watch them gather at blooming fields and roost in clusters in sheltered trees on cool evenings.
The resident butterflies are still numerous on warm days: painted ladies, American ladies, red admirals, and common buckeyes can be abundant in a big migration year, along with the last tiger and black swallowtails, great spangled fritillaries, orange and clouded sulphurs, and clouds of skippers. The goldenrod and asters are the indispensable late-season fuel for all of them — leave them standing. A sunny patch of fall flowers can be alive with butterflies right up until the first hard frost.
What to plant for them is in the Indiana native plants guide
Trees This Month
September is when Indiana's fall color begins in earnest, building from scattered early turners toward the October peak. The earliest and most reliable is black gum (tupelo), which flames deep crimson in the wet woods, joined by the red of sumac and Virginia creeper climbing the trunks and fences, the burgundy of flowering dogwood, and the first yellow of walnut, hickory, and ash — the ashes often dropping early. The sassafras begins its mix of orange, red, and gold.
This is peak mast season: the oaks drop acorns, the hickories and black walnuts rain down nuts, and the beeches drop their three-sided nuts, feeding the deer, turkeys, squirrels, and blue jays caching for winter. The pawpaws finish ripening and fall, and the persimmons of the southern hills soften toward edibility after the first frosts. The walnut leaves yellow and drop first, opening the canopy, and by late September the southern hills around Brown County are clearly tipping toward their famous autumn blaze.
Weather & Daylight
Across Indiana, a typical September day averages a high near 78°F and a low near 54°F, with about 3.3 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
Cooling gently to 78 by day and 54 at night, air turning crisper as the last humid stretches give way to early fall.
| Average high | 78°F |
|---|---|
| Average low | 54°F |
| Precipitation | 3.3 in |
| Sunrise (mid-month) | 7:25 ET |
| Sunset (mid-month) | 19:55 ET |
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 (ET).
Next month's version of this page, by email
One short note when Indiana's next month turns — what's arriving, blooming, and worth a night outside.
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Same month elsewhere: September in Iowa · September in Kansas · September in Kentucky