May is the explosive heart of Wisconsin spring — the peak of warbler migration, the height of the woodland wildflower bloom, and the moment the whole state finally turns green. Door County orchards blossom, the marshes teem with nesting birds, and warm-season planting begins after the last frost passes.
Week by week in May
April 30 – May 6
- Warbler migration peaks — a warm south wind can deliver twenty species in a single morning before the leaves fully close the canopy.
- Sheets of large-flowered trillium turn the maple-basswood woods and Kettle Moraine white at the height of the woodland bloom.
- Outdoor markets reopen statewide; asparagus, rhubarb, and the first tender spring greens arrive alongside seedlings and bedding plants.
May 7–13
- Horicon Marsh rings with yellow-headed blackbirds, marsh wrens, rails, American bitterns, and black terns at the height of the nesting season.
- Door County's cherry and apple orchards burst into blossom, a signature mid-May Wisconsin sight.
- Eastern tiger and black swallowtails take wing, and the first monarchs arrive from the south to lay eggs on emerging milkweed.
May 14–20
- Wild lupine colors the central sand-county oak barrens blue — the host plant of the endangered Karner blue butterfly.
- At Necedah NWR the reintroduced whooping cranes are nesting, while scarlet tanagers and orioles sing on territory in the leafing woods.
- The traditional safe date for tomatoes, peppers, and beans is near — set tender crops out around Memorial Day once frost danger passes.
May 21–27
- Leaf-out completes as the late oaks unfurl, and in the bogs the tamaracks finally break bud, flushing soft new needles.
- Prairie smoke, shooting star, and golden Alexanders open in dry prairies and on the Driftless ridgetops as the bloom shifts to sun.
- The endangered Karner blue begins its first flight in the central barrens, tied tightly to the blooming wild lupine.
May 28 – June 3
- Grassland birds sing on territory in the prairies — bobolinks, meadowlarks, dickcissels, and grasshopper sparrows over the Driftless grasslands.
- With frost finally past even up north, set out the last tomatoes, peppers, and squash, and direct-sow warm-season crops.
- Asparagus is at its peak alongside rhubarb, spinach, and the first pea shoots; the Dane County market rings Madison's Capitol Square.
Birds This Month
May is the grand crescendo of Wisconsin birding, when warbler migration peaks and the woods fill with color and song. Dozens of warbler species — blackburnian, magnolia, chestnut-sided, black-throated green, American redstart, and many more — pour through the treetops, joined by scarlet tanagers, rose-breasted grosbeaks, Baltimore orioles, indigo buntings, and great crested flycatchers. The lakeshore migrant traps, including Wisconsin Point in Superior and Lake Michigan's wooded parks, can be spectacular after a south wind.
The marshes are at their fullest now: Horicon Marsh rings with yellow-headed and red-winged blackbirds, marsh wrens, sora and Virginia rails, American bitterns, and black terns, while sandhill cranes and trumpeter swans tend young. At Necedah NWR, the reintroduced whooping cranes are nesting amid the wetlands.
This month's tip: bird the first two weeks of May at dawn after a warm southerly flow — the warbler wave can deliver twenty species in a single morning before the leaves fully close the canopy.
What's Blooming
May is the richest wildflower month in Wisconsin. The woodland floor reaches its peak just before full canopy: sheets of large-flowered trillium turn the maple-basswood forests and the Kettle Moraine white, joined by wild geranium, Jacob's ladder, Virginia bluebells in the Driftless river bottoms, wild columbine on rocky bluffs, jack-in-the-pulpit, mayapple, and the late ephemerals. In the central sand counties, the blue spikes of wild lupine color the oak barrens — the host plant of the endangered Karner blue.
As the woods leaf out, the bloom shifts to edges and openings: shooting star, golden Alexanders, and prairie smoke open in dry prairies and on the Driftless ridgetops. Door County's cherry and apple orchards burst into blossom mid-month, a signature Wisconsin sight, and gardens fill with tulips, lilac, and creeping phlox.
Garden This Month
May is the big planting month across Wisconsin, but timing hinges on frost. In the southern half, the last frost typically passes in early-to-mid May; in the north it can hold off until late May or even early June. The traditional safe date for setting out tender crops — tomatoes, peppers, beans, squash, cucumbers, and basil — is around Memorial Day for most of the state. Until then, keep planting and succession-sowing the cool-season crops: lettuce, spinach, peas, carrots, beets, and brassicas.
Harden off all indoor-started seedlings before they go in the ground, mulch beds to hold moisture, and watch the forecast — a late frost can still strike in mid-May. This is also the month to plant perennials, divide spring bloomers after they finish, and set out summer-blooming bulbs like gladiolus and dahlias once the soil warms. Keep an eye out for emerging pests as everything greens up at once.
Zone 4a (northern Wisconsin): the last frost often falls in late May or early June here, so hold tender crops until month's end. Keep planting cool-season greens, peas, and root crops, and harden off tomatoes and peppers for a Memorial Day or June planting.
Zone 5a (south-central & Madison): after mid-month, once frost danger passes, set out tomatoes, peppers, beans, squash, and cucumbers. Keep succession-sowing greens and carrots, and stay ready to cover for a late cold snap.
Zone 5b (Milwaukee & lakeshore): the lake-warmed southeast can plant warm-season crops by mid-to-late month — tomatoes, peppers, basil, and beans — though the lake also keeps spring cool, so watch soil temperatures before sowing heat-lovers.
What's at the Farmers Market
May markets surge back to life as the outdoor season opens statewide, including the famous Dane County Farmers' Market ringing Madison's Capitol Square. The defining spring crops arrive in volume: asparagus at its peak, rhubarb, tender spinach and lettuces, green onions, radishes, and the first spring greens and pea shoots. Wild ramps (wild leeks) and other spring specialties appear at some Driftless-area stands.
Bedding plants, vegetable seedlings, herb starts, and hanging baskets dominate the market for home gardeners now. Wisconsin cheese, eggs, honey, and the last of the maple syrup round things out. Choose asparagus with firm, tight tips and snap-fresh stalks; pick rhubarb with crisp, brightly colored stems and use both quickly, as the season's first produce is most tender and best within a day or two of the market.
Night Sky This Month
May's mild, comfortable nights make for easy stargazing, though the shortening darkness signals the approach of summer. Orange Arcturus in Boötes stands high overhead, and blue-white Spica in Virgo shines to the south. The Big Dipper rides high in the north, and the curved keystone of Hercules climbs in the east, carrying the great globular cluster M13, a fine binocular and telescope target from dark skies.
The Eta Aquariid meteor shower, debris from Halley's Comet, peaks in early May, though its low radiant favors the pre-dawn hours and southern horizon. Late in the night, the bright summer triangle of Vega, Deneb, and Altair begins to rise in the east, a preview of the season ahead. The dark northwoods skies remain excellent, with aurora possible on active nights.
For exact planet positions and the best viewing windows this month, see the printable Wisconsin night-sky guide for your part of the state.
Butterflies & Pollinators
May brings a strong butterfly season to Wisconsin as warmth becomes reliable and nectar floods the landscape. The big, conspicuous swallowtails take wing: the yellow-and-black eastern tiger swallowtail patrols river corridors and gardens, the black swallowtail works prairies and roadsides, and the giant swallowtail ranges north into the southern counties. Cabbage whites, orange sulphurs, spring azures, pearl crescents, and red admirals are common, and the first great spangled fritillaries emerge late in the month. The endangered Karner blue begins its first flight in the central sand-county oak barrens, tied tightly to the blooming wild lupine its caterpillars require. The first monarchs arrive from the south by mid-to-late May, the females laying eggs on the newly emerging milkweed that will fuel the summer's home-grown generations — a key reason to leave milkweed standing in gardens and roadsides.
What to plant for them is in the Wisconsin native plants guide
Trees This Month
May completes the leaf-out across Wisconsin, and the forest reaches full, fresh green. The sugar maples, basswoods, aspens, and birches are fully leafed, and the late-leafing oaks — bur, white, and red — finally unfurl and shed their catkins of pollen. Flowering trees crowd the calendar: black cherry, hawthorn, crabapple, and the white plumes of black locust, while Door County's orchard cherries and apples blossom in their famous mid-May display.
The conifers push new growth — white and red pines raise their pale "candles" of soft new needles, and spruces tip out in bright lime green. In the bogs, the tamaracks finally break bud, flushing their delicate soft needles, the last of Wisconsin's trees to fully leaf and a sign that spring has reached even the coldest ground.
The Wisconsin native plants guide covers what grows with them
Weather & Daylight
Across Wisconsin, a typical May day averages a high near 67°F and a low near 44°F, with about 3.9 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
Pleasant and blooming, warm 67F days give way to cool 44F evenings, with the wettest stretch of spring soaking the landscape.
| Average high | 67°F |
|---|---|
| Average low | 44°F |
| Precipitation | 3.9 in |
| Sunrise (mid-month) | 5:32 CT |
| Sunset (mid-month) | 20:17 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 Wisconsin's next month turns — what's arriving, blooming, and worth a night outside.
Go deeper with the Wisconsin guides
The complete Wisconsin birding, native-plant, and night-sky references — or the whole year, week by week, in one book.
Same month elsewhere: May in Wyoming · May in Alabama · May in Arizona