An Incomplete Wildflower Calendar for September

September 1 Small White Aster
September 2 Short’s Aster
September 3 Heart-Leaved Aster
September 4 New England Aster
September 5 Forsythia—Autumn Bloom
September 6 Autumn Crocus
September 7 Zigzag Goldenrod
September 9 Panicled Aster
September 22 Violet—Autumn Bloom
Late September to Late October: Witch Hazel

When-Then Phenology

When asters bloom in the waysides and bur marigolds flower in the swamps, then start cutting corn for silage.
When zigzag goldenrod blossoms in the woods, then the rose of Sharon shrubs will drop most of its flowers and the great decline of summer wildflowers begins in the fields.
When you see fallen leaves starting to accumulate in the backwaters and farm ponds, then the grapes on your grape arbor should be getting ripe, and half of your tomatoes and potatoes should be harvested.
When the first black walnut trees are almost bare, then the third cut of alfalfa is typically complete and farmers are preparing the soil for planting canola, grasses and small grains.
When bright patches of scarlet sumac and Virginia creeper mark the fencerows, and streaks of gold have appeared on the silver olive bushes, then kingbirds, finches, ruddy ducks, herring gulls and yellow-bellied sapsuckers move south. The last young grackles and hummingbirds leave their nests. Cedar waxwings fly south. Bobolinks and woodcocks follow.
When katydids refuse to chant and crickets songs are slow, then check for forecast and be ready to cover your tender flowers and vegetables: frost could be on the way that night.
When squirrels scatter buckeye hulls along the trails and locust pods fall beside them, then the first soybeans will be ready to harvest.
When you see farmers planting wheat in northern fields, know that throughout the South, cotton growers are defoliating their cotton plants, a process that increases fiber quality.
When doves stop calling in the mornings, then Fletcher scale
attacks arborvitae. Locust borers assault the locusts. Pine root collar weevils move to the pine trees.
When cobwebs are all over in the woods and butterflies multiply in the garden, that’s the time to plant your last lettuce and radishes of the year, complete the harvest of summer apples and start to pick the fall apples.
When you see red berries on the silver olives, orange berries on the American mountain ash, and purple berries on the pokeweed, then violet autumn crocuses blossom in town, and sandhill cranes have started their migration to the Gulf coast.
When you see young toads in the garden on the cooler evenings, then ragweed season will be at an end.
When the autumn leafturn starts along the 40th parallel, the deciduous trees are bare in northern Canada. In New England and in the Rocky Mountains, foliage colors are approaching their best.
When the huge pink mallows of the wetlands have died back, then the juniper tip midge appears on junipers, and gall adelgids attack the spruce threes.
When milkweed pods open, then late hosta bloom comes to a close in town. In the woods, middle spring’s sedum is growing stronger. Henbit, mint and catchweed revive as the canopy thins. Waterleaf has fresh shoots. Snow-on-the-mountain has recovered from its mid-summer slump and can be as thick and as beautiful as in early spring.
When most of the black walnuts have fallen and wood nettle seeds are black and brittle, then begin your autumn bulb planting and transplanting of perennials in the garden.
When the ash trees turn red and gold, then the season of killing frosts has arrived.
When the day’s length falls below 12 hours, then the sugar beet, pear, cabbage and cauliflower harvests commence in the Great Lakes region. In Wisconsin, Massachusetts, New Jersey, Oregon and Washington State, the cranberry harvest begins as berries darken in the cooler weather.
When goldenrod flowers are tufted and gray, then daddy longlegs disappear from the undergrowth and bird migrations reach their peak.

The Weeks of September

The Week the Last Wildflowers Bloom
In the last week of late summer, the final tier of wildflowers starts to open. White and violet asters, orange beggarticks, burr marigolds, tall goldenrod, zigzag goldenrod and Japanese knotweed come into bloom, blending with the brightest of the purple ironweed, yellow sundrops, blue chicory, golden touch-me-nots, showy coneflowers and great blue lobelia.
Deep in the woods, the late wildflowers of this year coincide with the first growth of second spring, actually the first days of next spring. March’s henbit comes up in the garden. The garlic mustard that will flower two Aprils from now sprouts in the rain. Wood mint puts out new stalks. Watercress revives in the sloughs. Next May's sweet rockets and next July’s avens send up fresh basal leaves. Scattered violets flower. Sweet Cicely sends out its foliage again. Sedum reappears, lanky from its canopied summer.
On the farm, pickle season is usually over, and peaches can be done for the year. Grapes are about to come in, and elderberries are deep purple and sweet for picking. Nearly half of the tobacco has usually been cut, half the commercial tomatoes have been picked, about a fourth of the potatoes dug.
Hickory nutting season opens as sweet-corn time winds down. Burrs from tick trefoil stick to your stockings when you wander off the trail. Lizard's tail drops its leaves into the creeks and sloughs. Beside the deer paths of the forests, the undergrowth is tattered and cluttered with the remnants of the year.
The last fireflies are flickering. Red-headed woodpeckers, red-winged blackbirds, house wrens, scarlet tanagers, indigo buntings, eastern bluebirds and black ducks migrate.

The Week of the Puffball Mushrooms
One of the first signs of early fall is the appearance of giant white puffball mushrooms in the woods. As the sun moves to within a few degrees of equinox, other creatures tell the time as well as puffballs. Sycamores, locust, elms, box elders, chinquapin oaks, lindens and redbuds show their autumn colors. Leaves gather in the backwaters and on sidewalks and paths. Sycamores are changing to a golden green, dogwoods to pink. Bright patches of scarlet sumac and Virginia creeper mark the fencerows. Some ash and cottonwoods are almost bare. Slippery elms are turning yellow-brown, and poplars fade.
The rich scent of late summer pollen is almost gone by end of the week, replaced by the pungent odor of fallen apples and leaves. Cicadas are dying. Bees are awkward and stiff in the cool mornings. Sometimes on sunny days, woolly bear caterpillars swarm across the roads. Kingbirds, finches, ruddy ducks, herring gulls and yellow-bellied sapsuckers move south.
Most berries are gone from the wild cherry trees when puffball mushrooms grow in the dark. The fat osage fruits are falling. Berries are red on the silver olives, orange on the American mountain ash, purple on the pokeweed. The domestic plants of local ponds are shriveling: the water lettuce, hyacinth and pickerel. The green frogs are finally silent.

The Time of Leafturn
When autumn leafturn starts near equinox in the Midwest, the deciduous trees are bare in northern Canada. In Oregon and Maine, foliage colors are approaching their best. In the Rocky Mountains, bull elks are mustering their harems, and snow is falling. Along the 40th parallel, the smoky tint of last week’s canopy quickly becomes clear and bright.
Now the soybean fields are yellow. Touch-me-nots are popping. Wood nettle seeds are black. Wingstem, clearweed and ironweed complete their cycle. Buckeyes are starting to burst from their hulls. More black walnuts, more hickory nuts, more acorns come down. The huge pink mallows of the wetlands have died, heads dark, leaves disintegrating. Scattered in the pastures, the milkweed pods are full, straining, ready to open. Mullein stalks stand bare like withered cacti. In the perennial garden, varieties of late hostas, like the August Moon and the Royal Standard, discard their petals.
Robin migration calls complement the chatter of the crows and jays and squirrels in the early mornings. Grackles are flocking in the fields. Cicada holidays become more frequent in the cooler afternoons. Sometimes katydids keep silence after dark, leaving the whole night to the great chorus of crickets.

The Week the Milkweeds Open
When the milkweed pods come open, then frost season is on the way, and Canadian geese, great-crested flycatchers, blue-gray gnatcatchers, ruby-throated hummingbirds, eastern wood peewees and bank swallows move down their flyways toward the Gulf of Mexico. Buzzards gather at their roosts. Crows are the only birds to call before dawn. Monarch butterflies become more numerous, still visit the late phlox and the zinnias in the afternoon sun; other insects, however, become less common in the field and garden as the number of pollen-bearing flowers dwindles. Spiders understand; they weave fewer webs. Bees compete for the remaining nectar. Winter’s craneflies swarm, a fraction of their December size.
When milkweed pods open, peak leaf coloration starts in northern New England. In the Mid-Atlantic States, fallen leaves begin to cover the undergrowth, and the canopy is visibly thinning. Honey locusts are half yellow, buckeyes in the middle of full leafdrop. Hickories are gold, like the ashes. The first white mulberry, sycamore and cottonwood leaves have come down in the wind.
Barberies are red, and rose hips have turned alongside them. Touch-me-nots are still blooming, but their foliage deteriorates. Late summer’s clearweed has green seeds. Older wingstem and ironweed are done blossoming. Wild lettuce leaves are stained with decay. Queen Anne's lace and bright blue chicory die back suddenly. The first goldenrod is brown. White vervain is gray, streaked with maroon, tattered, laced from insects. Boneset is rusting. Beggarticks are ready to stick to your clothing. Roadside sunflowers and Jerusalem artichokes enter their final week.