Pennsylvania Nature Guide: September 2026
Data updated: August 2026Sources & method · Corrections
September is the great turn into autumn in Pennsylvania — the world-famous raptor migration peaks over Hawk Mountain, the monarchs stream south, the warblers pour back through, and the first brilliant fall color flushes the Allegheny and Pocono highlands.
Week by week in September
September 3–9
- The raptor migration over Hawk Mountain builds — the world's first refuge for birds of prey lights up on every cold front.
- Goldenrod and the full glory of the asters peak — brilliant purple New England aster and tall ironweed across the meadows.
- Harvest winter squash and potatoes, plant garlic toward week's end, and sow cover crops in cleared beds.
September 10–16
- Broad-winged hawks pour over Hawk Mountain in spectacular 'kettles,' sometimes thousands in a single day — the autumn raptor climax.
- The monarch migration streams south along the ridges and Lake Erie shore, nectaring in waves on goldenrod and aster.
- Apples pour in from Adams County orchards alongside the last peaches and the first Concord grapes from the Lake Erie belt.
September 17–23
- Warbler migration is at full flood in fall plumage, and Presque Isle on Lake Erie concentrates migrants spectacularly.
- The autumn equinox near the 22nd returns long nights, with the Andromeda Galaxy now well placed for binoculars.
- Fall color flushes into the high Allegheny and Pocono country — the leading edge of the spectacular October show.
September 24–30
- White-throated sparrows and dark-eyed juncos arrive for the winter as the first big goose and tundra swan flocks move down the flyways.
- The first mountain frost arrives — harvest tender crops, plant garlic, and divide perennials while the soil holds warmth.
- The monarch migration climaxes — dozens drift through after a cold front, all bound for central Mexico.
Birds This Month
September is Pennsylvania's autumn birding spectacle, and the headline is the raptor migration over Hawk Mountain Sanctuary — the world's first refuge for birds of prey, perched on a Kittatinny Ridge lookout where thousands of hawks stream past on northwest winds. Mid-September brings the great rivers of broad-winged hawks, sometimes thousands in a single day boiling up in 'kettles,' joined by ospreys, bald eagles, American kestrels, sharp-shinned hawks, and peregrine falcons. Ridge hawk-watches statewide light up on every cold front.
The songbird migration is also at full flood. The warbler migration reverses, drabber now in fall plumage, and Presque Isle State Park on Lake Erie concentrates migrants spectacularly. Ruby-throated hummingbirds pass through and depart, common nighthawks stream south in evening flocks, and sparrows, thrushes, and the first white-throated sparrows and juncos arrive. Shorebirds continue on the mudflats. Watch the ridges on the day after a cold front for the heaviest raptor flights of the year.
What's Blooming
September is the peak of Pennsylvania's fall meadow bloom, the fields a sea of gold and purple. Goldenrod of many species blankets the meadows and roadsides, joined by the full glory of the asters — brilliant purple New England aster, blue smooth and heart-leaved asters, and white heath and calico asters — along with tall ironweed, joe-pye weed, boneset, sneezeweed, and great blue lobelia in the wet meadows.
The wet edges hold the last cardinal flower and abundant orange jewelweed, while the roadsides keep Queen Anne's lace, chicory, and the climbing white flowers of virgin's bower (wild clematis). In gardens, asters, sedum, sunflowers, zinnias, dahlias, and ornamental grasses peak. This goldenrod-and-aster bloom is the year's last great nectar feast, critical fuel for the migrating monarchs and for bees building their winter stores. The display fades through the month as the first frosts arrive in the mountains, but the lowland meadows hold their color into October.
Garden This Month
September is the harvest-and-transition month in Pennsylvania gardens. The summer crops wind down — pick the last tomatoes, peppers, eggplant, beans, cucumbers, summer squash, and melons — and the fall harvest comes in: winter squash, pumpkins, potatoes, the first frost-sweetened greens, broccoli, cabbage, kale, carrots, beets, and apples. In the mountains, the first frost can strike by late month, so watch the forecast and harvest or cover tender crops on cold nights.
This is the prime time to plant for next year and protect the soil. Sow cover crops (winter rye, oats, or clover) in cleared beds to build and hold the soil over winter, and sow a final round of fast cool-season greens and radishes. Toward month's end, begin planting garlic for next summer's crop, and divide and transplant perennials while the soil is still warm. Pull and compost spent summer plants, clean up diseased debris, and start the slow shift from harvest to autumn cleanup and planning.
Zone 5b (Allegheny & northern uplands): the first frost typically arrives in late September. Harvest tender crops ahead of frost or be ready to cover them, bring in winter squash and the last tomatoes, and plant garlic and cover crops.
Zone 6a (ridge-and-valley & central uplands): frost nears by late September to early October. Keep harvesting and have row cover ready for the first cold nights; sow a final round of fast greens and plant garlic toward month's end.
Zone 7a (southeastern Piedmont): still frost-free most of the month. Keep the fall garden growing, sow spinach and lettuce, harvest the warm-season crops, and prepare beds for garlic planting in October.
What's at the Farmers Market
September markets bridge summer and fall, holding the last of the warm-season crops while the autumn harvest arrives. The first apples pour in from Adams County and orchards statewide, alongside the last peaches, the first pears, and the year's fall raspberries and Concord grapes from the Lake Erie grape belt. The vegetable tables still carry tomatoes, peppers, eggplant, sweet corn, and melons, now joined by winter squash, pumpkins, potatoes, cabbage, broccoli, cauliflower, and greens.
Pennsylvania's Kennett Square mushrooms stay abundant, and fresh cider, honey, and cut flowers brighten the stands. Choose apples that are firm and heavy with good color and store them cold, away from other produce; pick winter squash with hard, unblemished rinds and an intact stem for long keeping; and select Concord grapes that are deep purple, fragrant, and firmly attached to the stem. This is the richest, most varied moment of the market year, with both summer and fall on the tables at once.
Night Sky This Month
September's autumn equinox near the 22nd brings the return of long, comfortable nights, and the sky shifts toward fall. The Summer Triangle of Vega, Deneb, and Altair still rides high after dusk, but the autumn constellations climb in the east — the Great Square of Pegasus, the W-shaped Cassiopeia overhead, and the Andromeda Galaxy (M31), the farthest object visible to the naked eye, faintly visible from a dark site and lovely in binoculars.
There is no major meteor shower peaking this month, so September favors deep-sky observing under the lengthening nights, with the late-summer Milky Way still arching overhead. The mild evenings and clearer autumn air make for excellent viewing at dark sites like Cherry Springs State Park. Watch the eastern horizon late at night for the first winter stars beginning to rise. The printable Pennsylvania night-sky guide lists this year's exact planet positions, conjunctions, and the dark-sky sites best for your region as the autumn observing season opens.
Butterflies & Pollinators
September is the climax of the monarch migration in Pennsylvania. The migratory generation streams south, following the ridges and the Lake Erie shore, pausing to nectar in waves on the blooming goldenrod, asters, and ironweed. On a good day after a cold front, dozens or hundreds may drift through, all heading for the overwintering forests of central Mexico — one of the great spectacles of the insect world, visible from any goldenrod field or ridgetop hawk-watch.
Other migrants and late-season butterflies fill the warm afternoons: common buckeyes are abundant now, painted ladies, red admirals, and cloudless sulphurs drift through, and the orange and clouded sulphurs, cabbage whites, pearl crescents, and skippers still work the flowers. The last great spangled fritillaries and swallowtails fade. The goldenrod-and-aster bloom is the season's final great nectar source — the best thing a gardener can do for the migrating monarchs is to keep native asters and goldenrod blooming through the month.
What to plant for them is in the Pennsylvania native plants guide
Trees This Month
September begins Pennsylvania's celebrated fall color, the change starting in the cool, high country and creeping down and south. The early-turning trees lead: black gum (tupelo) and sourwood flush deep scarlet, the sassafras turns orange and red, the sumacs blaze crimson along the roadsides, and the first red and sugar maples color up in the wet spots and the Allegheny highlands. Black walnut, birch, and ash begin to yellow.
The autumn mast drop is underway — the oaks rain down acorns, the hickories and black walnuts drop their nuts, and the beech sheds its three-sided nuts — a crucial harvest for deer, bears, turkeys, and squirrels. The conifers stay green: the eastern hemlock, the state tree, and the eastern white pine anchor the darkening woods. By late September the Pocono and Allegheny highlands are flushing into color, the leading edge of the spectacular October show that will sweep the whole state.
The Pennsylvania native plants guide covers what grows with them
Weather & Daylight
Across Pennsylvania, a typical September day averages a high near 74°F and a low near 52°F, with about 4.3 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
A gradual easing from summer's grip, warm days and cooling nights arrive alongside steady, lingering rain showers.
| Average high | 74°F |
|---|---|
| Average low | 52°F |
| Precipitation | 4.3 in |
| Sunrise (mid-month) | 6:51 ET |
| Sunset (mid-month) | 19:21 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 Pennsylvania's next month turns — what's arriving, blooming, and worth a night outside.
Go deeper with the Pennsylvania guides
The complete Pennsylvania birding, native-plant, and night-sky references — or the whole year, week by week, in one book.
Same month elsewhere: September in Rhode Island · September in South Carolina · September in South Dakota