Delaware Nature Guide: September 2026
Data updated: August 2026Sources & method · Corrections
September is the great turn toward fall in Delaware — the monarchs and songbirds stream south along the coast, the first cool fronts trigger the autumn raptor flights at Cape Henlopen, and the markets carry the last of summer into the first of fall. The marshes blaze with goldenrod and asters.
Week by week in September
September 3–9
- The monarch migration streams south along the coast, concentrating at Cape Henlopen to nectar on seaside goldenrod after each front.
- Peak songbird migration pours through the woods — blackpoll, Cape May, and many warblers with tanagers and grosbeaks.
- The autumn equinox nears; Pegasus, Andromeda, and Cassiopeia climb the eastern sky as the Summer Triangle still rides high.
September 10–16
- Cold fronts send sharp-shinned hawks, kestrels, merlins, and peregrines streaming down the coast past Cape Henlopen.
- New England aster deepens purple as the goldenrod-and-aster bloom peaks across the meadows and marshes.
- Plant garlic toward month's end and sow cover crops on emptying beds while the soil stays warm.
September 17–23
- The first returning ducks and green-winged teal arrive in the impoundments as the early waterfowl trickle back.
- Apples, pears, winter squash, pumpkins, and sweet potatoes fill the stands as fall arrives in force.
- Black gum blazes scarlet and dogwoods deepen to maroon, hung with red fruit for the migrating thrushes.
September 24–30
- On good mornings after a northwest wind, hundreds of monarchs drift past Cape Henlopen — a moving river of orange.
- Sparrow diversity peaks in the brushy fields as white-throated and white-crowned sparrows and juncos arrive for winter.
- The Andromeda Galaxy, the most distant naked-eye object, can be glimpsed from a dark Cape Henlopen sky in the crisp fall air.
Birds This Month
September is one of Delaware's premier birding months, the heart of fall migration. Songbird migration peaks: waves of warblers — blackpoll, black-throated blue, magnolia, American redstart, Cape May, and many more — pour through the woods, along with vireos, flycatchers, thrushes, tanagers, and rose-breasted grosbeaks, concentrating at coastal migrant traps. Cape Henlopen becomes a funnel as birds pile up at the point before crossing the bay.
Each cold front triggers the autumn raptor flight: sharp-shinned and Cooper's hawks, American kestrels, merlins, peregrine falcons, ospreys, broad-winged hawks, and bald eagles stream down the coast. Shorebird migration continues at Bombay Hook and Prime Hook, with juveniles now dominating, and the first returning ducks and green-winged teal arrive in the impoundments. Chimney swifts and nighthawks stream south at dusk.
This month's tip: bird Cape Henlopen State Park the morning after a northwest cold front, when migrant songbirds, monarchs, and raptors concentrate at the point — one of the most exciting migration spectacles on the Delaware coast.
What's Blooming
September is the peak of Delaware's fall wildflower bloom, a blaze of gold and purple. The goldenrods reach their full flood across every field, roadside, and dune — seaside goldenrod brilliant along the coast at Cape Henlopen — joined by the asters coming into their own: New England aster deep purple, New York, calico, and heath asters, and the white frost aster. Ironweed, joe-pye weed, and boneset finish in the wet meadows.
The tall sunflowers and their kin shine — Jerusalem artichoke, tickseed sunflower, and wingstem — and in the tidal marshes the groundsel tree and marsh elder whiten the edges while the saltmarsh asters bloom. This goldenrod-and-aster surge is the critical nectar fuel for the migrating monarchs staging at the coast and the late pollinators. It is one of the most beautiful and ecologically important flowerings of the Delaware year, the meadows humming right up to the first frost.
Garden This Month
September is the harvest-and-transition month in the Delaware garden. The summer crops finish their run — gather the last tomatoes, peppers, eggplant, beans, melons, and winter squash as they ripen — while the fall garden sown in August comes into its prime: spinach, lettuce, arugula, radishes, turnips, kale, collards, broccoli, and cabbage thrive in the cooling weather, the brassicas and greens actually sweetening as nights cool. There is still time in the lower counties to sow quick crops like spinach, radishes, and lettuce.
This is the month to plant garlic toward its end for next summer's crop, and to sow cover crops like winter rye and crimson clover on emptying beds to protect and build the soil. Divide and plant perennials while the soil is still warm and the rains return, and set out spring-flowering bulbs late in the month. Keep watering as needed, pull spent plants, and start a fall cleanup, though leaving seed heads and some leaf litter benefits the overwintering insects and birds. The cooler, easier gardening weather is a welcome relief after the humid summer.
Zone 7a (northern New Castle County): the first frost can arrive in mid-to-late October here, so harvest the last tomatoes and peppers ahead of it, keep fall greens and brassicas going, and plant garlic and spring bulbs late in the month.
Zone 7b (Kent, Sussex, and the coast): the mild lower counties hold a long fall — keep sowing quick fall greens like spinach, lettuce, and radishes, harvest summer crops, and plant garlic and cover crops as beds open up.
What's at the Farmers Market
September markets in Delaware bridge summer and fall. The last of summer lingers — vine-ripe tomatoes, peppers, eggplant, sweet corn, melons, okra, and the final peaches — while autumn arrives in force: apples, Asian and European pears, winter squash, pumpkins, sweet potatoes, broccoli, cauliflower, cabbage, and fresh greens fill the stands. The grape harvest and the first cider appear.
From the Delaware Bay, blue crabs remain in good fall season — choose live, lively, heavy crabs, keep them cold and damp, and cook them the day you buy. Choose apples that are firm and heavy and store them cold and separate from other produce, and pick winter squash and pumpkins with hard, unblemished rinds and an inch of dry stem for long keeping. Choose the last tomatoes heavy and fragrant and use them quickly, and pick greens with crisp leaves. The Delaware market is at its most abundant and varied of the whole year, two seasons' harvests overlapping on the table.
Night Sky This Month
September brings the autumn equinox and a transitional sky. The Summer Triangle of Vega, Deneb, and Altair still rides high in the early evening, with the Milky Way arching overhead, while the autumn constellations climb in the east: the Great Square of Pegasus, the chained figure of Andromeda, and the W of Cassiopeia. From a truly dark Delaware sky, the Andromeda Galaxy — the most distant object visible to the unaided eye — can be glimpsed as a faint smudge near Cassiopeia.
The cooler, drier air of early fall brings excellent transparency, and around the equinox day and night reach balance. There is no major meteor shower this month, so September favors the deep-sky objects of the overhead Milky Way and the rising autumn galaxies. The shorter nights of summer give way to lengthening dark. Seek the darkest skies at Cape Henlopen and the lower Sussex coast, away from the Wilmington and Dover light.
Exact planet positions vary year to year — the printable Delaware night-sky guide carries the current planet and Moon details for your part of the state.
Butterflies & Pollinators
September is the month of the monarch migration in Delaware, the cluster's signature autumn spectacle. As cold fronts push through, the season's final super-generation streams south along the Atlantic coast, and they concentrate at Cape Henlopen and along the Delaware Bay shore, nectaring heavily on seaside goldenrod and asters in the dunes before crossing or following the coastline toward Mexico. On a good morning after a northwest wind, dozens to hundreds drift past the point — a moving, fragile river of orange.
Other migrants move with them: common buckeyes, painted and American ladies, cloudless and sleepy sulphurs, and red admirals stream down the coast, and the late skippers work the goldenrod. The resident eastern tiger and spicebush swallowtails wind down their final brood. Keep nectar flowers — goldenrod, asters, zinnias, and lantana — blooming to fuel the migrants, and watch the coast after each front for the peak monarch flights of the First State year.
What to plant for them is in the Delaware native plants guide
Trees This Month
September is when Delaware's trees begin their turn toward fall color. The earliest species lead: black gum blazes scarlet, the most brilliant early color in the state, and sassafras turns orange, red, and gold while sumac reddens the roadsides. The flowering dogwoods deepen to maroon and hang heavy with red fruit, feeding the migrating thrushes and robins, and the red maples in the wet woods show their first early flares.
The mast harvest peaks: the oaks drop acorns, the hickories and black walnuts shed nuts, and the beech sets its triangular nuts — a feast for jays, squirrels, and deer. American holly, the state tree, carries its berries toward full red. The bulk of the canopy — the oaks, tulip trees, sweetgums, and hickories — is still green or just beginning to fade, holding its color for October's full display. The shortening days and cool nights are setting the chemistry of the autumn change in motion across the low coastal-plain woods.
The Delaware native plants guide covers what grows with them
Weather & Daylight
Across Delaware, a typical September day averages a high near 79°F and a low near 59°F, with about 4.2 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
Summer eases into early fall, warm 79-degree days and comfortable upper-50s nights, with rain still frequent but the air less oppressive.
| Average high | 79°F |
|---|---|
| Average low | 59°F |
| Precipitation | 4.2 in |
| Sunrise (mid-month) | 6:43 ET |
| Sunset (mid-month) | 19:12 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).
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One short note when Delaware's next month turns — what's arriving, blooming, and worth a night outside.
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Same month elsewhere: September in Washington, D.C. · September in Florida · September in Georgia