May is the explosion of Wyoming spring — arrowleaf balsamroot and lupine sweeping the foothills gold and blue, the full surge of migrant songbirds through the river corridors, and newborn pronghorn and bison calves on the range. It is one of the state's two finest birding months, though snow can still fall in the mountains.
Week by week in May
April 30 – May 6
- Balsamroot and silvery lupine paint the Jackson Hole hills gold and blue, the signature color combination of the Wyoming spring.
- The warbler and tanager wave peaks in the river cottonwoods — yellow warblers, western tanagers, black-headed grosbeaks, and lazuli buntings.
- The minor Eta Aquariid meteor shower, debris of Halley's Comet, peaks around May 6 low in the predawn southern sky.
May 7–13
- Bullock's orioles, warbling vireos, and broad-tailed hummingbirds trill through the leafing cottonwoods and aspen as breeding gets underway.
- Scarlet gilia, the first Indian paintbrush, sticky geranium, and larkspur open across the foothills as the wildflower season accelerates.
- In the warmer basins set out tomatoes and squash under walls-of-water after mid-month, but hold everything tender in the high valleys.
May 14–20
- Wetlands teem with avocets, black-necked stilts, white-faced ibis, and Forster's and black terns as the mountain canyons begin to wake.
- Big western tiger swallowtails begin patrolling the cottonwood and willow river corridors as the foothill butterfly diversity swells.
- Serviceberry, chokecherry, and wild plum fill the draws and canyon mouths with white and pink bloom as the aspens flush green upslope.
May 21–27
- The foothills are at full glory — balsamroot, lupine, paintbrush, geranium, and scarlet gilia woven across the sagebrush slopes.
- Newborn pronghorn and bison calves appear on the range as Sandhill Cranes settle on eggs in the wet meadows of Jackson Hole.
- Outdoor markets open in the larger towns with rhubarb at its peak, the first asparagus, and a wave of hoop-house greens.
May 28 – June 3
- The frost-free window opens in the basins — set out the last tomatoes, peppers, and squash and direct-sow beans, corn, and cucumbers.
- The subalpine forests wake as snow recedes, filling with dusky flycatchers, green-tailed towhees, and breeding montane songbirds.
- Glacier lily and spring beauty open at the very edge of the melt in the Tetons and Wind Rivers, the first wave of the alpine bloom.
Birds This Month
May is the peak of Wyoming's spring migration and breeding song, the second of the two best birding months. The riparian cottonwood corridors of the Green, Snake, and North Platte fill with migrants — yellow warblers, Wilson's, MacGillivray's, yellow-rumped, and Townsend's warblers, western tanagers, black-headed grosbeaks, lazuli buntings, bullock's orioles, and warbling vireos — pouring through and settling to nest. The sagebrush sea is in full song with Sage Thrasher, Brewer's and sagebrush sparrow, and vesper sparrow, while the last Greater Sage-Grouse leks wind down.
Wetlands and meadows teem: American avocets, black-necked stilts, Wilson's phalaropes, willets, marbled godwits, white-faced ibis, Forster's and black terns, and broods of early ducks at Seedskadee NWR and Ocean Lake. Sandhill Cranes are on eggs in the wet meadows of Jackson Hole, mountain bluebirds feed nestlings, and the high country wakes as snow recedes — green-tailed and spotted towhees, dusky flycatchers, and broad-tailed hummingbirds trilling through the aspen.
This month's tip: work the river cottonwoods at dawn for the warbler and tanager wave, and don't overlook the mountain canyons as they open — the aspen and willow zones come alive with breeding birds the moment the snow lets go.
What's Blooming
May is when Wyoming's foothills truly ignite. The bright yellow arrowleaf balsamroot sweeps across sagebrush slopes and benches statewide, most famously painting the hills of Jackson Hole and the Wind River and Bighorn fronts gold, mixing with the deepening blue of silvery lupine for the signature combination of the Wyoming spring. With them open scarlet gilia, the first Indian paintbrush in reds and oranges, sticky geranium, larkspur, death camas, and the white plates of serviceberry and chokecherry blossom in the draws. On the dry prairie and benches biscuitroot, prairie smoke, milkvetch, and the cushions of phlox and cushion buckwheat bloom in profusion. The high mountains begin to wake at their lowest edges as snow recedes, but the true alpine bloom is still weeks off in the Tetons and Wind Rivers.
Garden This Month
May is the busiest planting month across most of Wyoming, but it is a month that demands caution about frost. In the warmer basins the last frost passes mid-to-late May, opening the door to set out tomatoes, peppers, eggplant, and squash and direct-sow beans, corn, and cucumbers — but in the high valleys and on cold nights statewide, frost and even snow can strike right through the month, so keep row cover, cold frames, and walls-of-water at hand. Finish the cool-season garden of peas, lettuce, spinach, carrots, beets, and onions early so it matures before summer heat.
Harden off transplants gradually to Wyoming's intense high-altitude sun and drying wind, which can scorch tender seedlings in a day. Mulch to hold the moisture that the wind steals from new beds, water deeply, and plant on the calendar's late side rather than gambling on an early warm spell — the cold usually comes back. Keep an eye out for cutworms and flea beetles as the soil warms.
Zone 3b (Jackson Hole, high valleys): the cool-season garden goes in now — sow peas, spinach, lettuce, radishes, and carrots and set out hardened brassicas, but hold every warm-season crop until June; frost and even snow remain routine here all month. Keep walls-of-water and row cover ready.
Zone 4a (high basins, Lander, Cody): finish the cool-season planting and, near month's end after the frost date passes, begin setting out tomatoes, peppers, and squash under protection. Harden everything off slowly to the wind and sun.
Zone 4b (warmer basin towns, Torrington area): the main planting month — set out tomatoes, peppers, and squash after mid-May once frost risk fades, direct-sow beans and corn, and keep the cool-season succession going.
What's at the Farmers Market
Wyoming's outdoor farmers markets begin opening in May in the larger towns, and the tables show the first real spring abundance. Expect rhubarb at its peak, the first cuttings of asparagus from established beds, and a wave of cool-weather greens — spinach, lettuce, arugula, kale, salad mix, radishes, green onions, and salad turnips — from hoop houses and early gardens. The state's grass-fed beef, lamb, and bison remain mainstays from local ranches.
This is also bedding-plant and seedling season; markets fill with vegetable starts, herbs, and flower transplants for gardeners racing the short season. Look for Wyoming honey, eggs, and last summer's jarred preserves and chokecherry jelly. Eat the asparagus and rhubarb within a day or two and refrigerate them, and keep tender greens crisp and cold for quick use.
Night Sky This Month
May nights are comfortable and still long enough for good observing under Wyoming's dark skies before the short summer nights arrive. The Red Desert and southwest basins, and the backcountry of Yellowstone and Grand Teton, remain premier dark-sky destinations, with town-edge sites near Lander, Pinedale, and Saratoga easily showing the Milky Way. Spring star parties begin to gather under these skies as the nights warm.
Spring fills the sky: Leo rides high in the west, the Big Dipper stands overhead, and its handle arcs to brilliant orange Arcturus in Boötes and on to blue-white Spica in Virgo. The faint spring galaxy field through Virgo and Coma is at its best, and by late evening the Summer Triangle of Vega, Deneb, and Altair climbs in the east, heralding the season ahead. The minor Eta Aquariid meteor shower, debris of Halley's Comet, peaks around May 6, low in the predawn south.
Exact planet positions shift year to year — the printable Wyoming night-sky guide lists this season's planet visibility and the darkest viewing sites near you.
Butterflies & Pollinators
May builds Wyoming's butterfly fauna rapidly as warmth climbs the foothills. The big western tiger swallowtails begin patrolling the cottonwood and willow river corridors, and the first two-tailed and pale swallowtails appear in the canyons. Over the balsamroot and lupine slopes the diversity swells — western whites, Sara orangetips, clouded and orange sulphurs, a growing roll of blues (Melissa, silvery, boisduval's), spring azures, and the first small coppers and hairstreaks. Painted ladies stream north in migration years, and the overwintered mourning cloaks are now worn and fading. On the warm sage flats watch for checkered skippers and the first grass skippers. The high-country specialties — the Rocky Mountain parnassian and the alpine fritillaries and blues — are still locked under snowpack in the Tetons and Wind Rivers, weeks from their brief summer flight. Plant and watch the early nectar — balsamroot, biscuitroot, and the first paintbrush draw the season's growing crowd.
What to plant for them is in the Wyoming native plants guide
Trees This Month
May leafs out Wyoming's mountains as well as its valleys. The plains cottonwoods finish leafing in full along the river bottoms, casting fresh green shade over the Green, Snake, and North Platte, and the quaking aspens flush their hillsides bright translucent green as the snowline retreats up the Tetons, Snowies, and Bighorns. The flowering shrubs peak: white plates of serviceberry and chokecherry and the white-pink of wild plum fill the draws and canyon mouths, and the willows and alders green the stream edges.
The conifers push new growth. Douglas-fir, Engelmann spruce, subalpine fir, and lodgepole pine flush soft new needles on the montane slopes, and the high limber pines green at the snow's edge on the ridges. Watch the flowering chokecherry and serviceberry for nectaring butterflies and for cedar waxwings, and the leafing aspens for nesting warbling vireos, house wrens, and red-naped sapsuckers drilling their neat sap wells.
Weather & Daylight
Across Wyoming, a typical May day averages a high near 62°F and a low near 36°F, with about 2.4 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
Warm afternoons in the low 60s meet cool nights, with the year's wettest stretch bringing frequent showers and soggy soil.
| Average high | 62°F |
|---|---|
| Average low | 36°F |
| Precipitation | 2.4 in |
| Sunrise (mid-month) | 5:47 MT |
| Sunset (mid-month) | 20:24 MT |
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 (MT).
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One short note when Wyoming's next month turns — what's arriving, blooming, and worth a night outside.
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Same month elsewhere: May in Alabama · May in Arizona · May in Arkansas