May is Idaho's wildflower climax in the low and mid country — the Camas Prairie turns lake-blue with camas, the foothills peak in balsamroot and lupine, and migration brings the last songbirds north. It is one of the very best months to be outdoors anywhere in the state below the high snowline.
Week by week in May
April 30 – May 6
- Migration peaks as Yellow, Wilson's, and MacGillivray's Warblers fill the riparian corridors and Western Kingbirds arrive on the open country.
- The Eta Aquariid meteors, debris from Halley's Comet, peak low in the predawn east around May 5–6.
- Arrowleaf balsamroot and silvery lupine blanket the Boise Front in gold and blue at the foothills' wildflower peak.
- Direct-sow beans and squash and set out tomatoes with protection as the Treasure Valley frost date approaches.
May 7–13
- Camas begins turning the Centennial Marsh and Camas Prairie lake-blue, one of the Intermountain West's great bloom spectacles.
- American Avocets, Black-necked Stilts, and Wilson's Phalaropes nest in the wetlands as Western Meadowlarks sing across the sagebrush.
- Set out tomatoes, peppers, and squash after mid-month once frost has passed in the warm Treasure Valley.
- The first strawberries arrive from southwestern Idaho alongside abundant rhubarb, spinach, and green onions.
May 14–20
- The Camas Prairie hits its blue peak near Fairfield as bitterroot and death camas bloom on the foothill slopes.
- Western Tailed-Blues, checkerspots, and the year's first fritillaries nectar on the blooming camas and lupine across the low country.
- Calliope and Black-chinned Hummingbirds work the foothill bloom, and Bullock's Orioles weave hanging nests in the cottonwoods.
- Direct-sow sweet corn and beans and mulch the potatoes and onions as the dry summer approaches.
May 21–27
- Camas finishes on the prairie as scarlet gilia, penstemons, and the first mid-elevation meadow flowers open up the mountainsides.
- Sandhill Cranes tend colts in the eastern Idaho meadows, and the high meadows fill with Mountain Bluebirds feeding fledglings.
- Asparagus, salad greens, peas, and the first greenhouse tomatoes crowd the markets as bedding plants sell fast.
- Ponderosa pine and the state tree western white pine push soft new candles as the conifers flush spring growth.
May 28 – June 3
- Syringa, the white state flower, begins its sweet-scented bloom along the Clearwater, Salmon, and Snake canyon slopes.
- Common Nighthawks boom at dusk and Lazuli Buntings sing from the foothill brush as breeding hits full stride.
- Plant the warm-season garden in the cooler high valleys now that frost has passed, using quick-maturing varieties.
- Western Tiger Swallowtails float the willow-lined river bottoms as the lowland butterfly flight grows varied and abundant.
Birds This Month
May is peak migration and the height of breeding song in Idaho. The riverside cottonwoods and foothill brush fill with Bullock's Orioles, Black-headed Grosbeaks, Lazuli Buntings, Yellow, Yellow-rumped, Wilson's, and MacGillivray's Warblers, Western Tanagers, Western Kingbirds, and Vaux's Swifts. Calliope, Rufous, Black-chinned, and Broad-tailed Hummingbirds work the foothill bloom, and the sagebrush sings with Sage Thrasher, Brewer's Sparrow, and Western Meadowlark.
The Snake River Birds of Prey NCA nestlings are growing under the cliffs, and wetlands brim with American White Pelicans, Western and Clark's Grebes in their rushing courtship runs, White-faced Ibis, Black-necked Stilts, American Avocets, and Wilson's Phalaropes. Long-billed Curlews display over the Camas Prairie, Sandhill Cranes tend colts in the eastern valleys, and shorebirds stop on the mudflats during the heart of spring passage.
What's Blooming
May is the great wildflower month across Idaho's low and mid elevations. The headline is the Camas Prairie near Fairfield and the Centennial Marsh, where camas (Camassia quamash) turns the wet prairie sheets of lake-blue in late May — one of the most famous bloom spectacles in the Intermountain West. The foothills peak too: arrowleaf balsamroot and silvery lupine blanket the Boise Front and canyon slopes in gold and blue, with paintbrush, larkspur, bitterroot, and death camas woven through.
The canyon grasslands of the Salmon, Snake, and Clearwater are at their fullest, and the mid-elevation meadows green and bloom as the snowline climbs. Wild blue flax, scarlet gilia, penstemons, and mariposa lilies open on the warming slopes. The high Sawtooth and Lost River basins are still melting out, their alpine display a month or two away, so May's glory is the prairie and the foothills.
Garden This Month
May is planting-out month for the warm-season garden across most of Idaho. In the Treasure Valley and southwestern valleys, the frost date passes mid-month and the big crops go in: set out tomatoes, peppers, and eggplant, and direct-sow sweet corn, beans, squash, cucumbers, and melons — the famous Idaho sweet corn and potatoes thrive on the long, hot days ahead. Keep succession-sowing lettuce, carrots, and beets, and harvest the spring peas, radishes, and greens.
Timing is everything in this clear-sky state: hold tender transplants until nights reliably warm and frost has passed, using row cover or walls-of-water against late cold snaps, which strike the eastern plain and mountain valleys well into the month. Mulch the potatoes and onions, water consistently as the dry summer approaches, and stake tomatoes early. In the high valleys, the season is only now cracking open, so lean on the hardiest, quickest-maturing varieties to fit Idaho's short mountain summer.
Zone 4b (eastern Snake River Plain & mountain valleys): the short season finally opens. Sow hardy greens, peas, and potatoes, but hold tomatoes and squash under cover until very late May or June — frost can still strike the high valleys deep into the month.
Zone 5b (Boise foothills & Magic Valley): plant warm-season crops toward the end of May once nights warm and frost is safely past. Direct-sow beans and squash, set out tomatoes with protection early on, and keep the cool-season harvest going.
Zone 6a (warmest Treasure Valley & lower Snake River): set out tomatoes, peppers, squash, beans, and sweet corn after mid-month once frost has passed. Keep succession-sowing greens and carrots, harvest spring radishes and lettuce, and water in the new transplants.
What's at the Farmers Market
May markets across Idaho fill out as the spring season hits stride and outdoor farmers markets open in earnest. The first true field crops arrive: asparagus from the warm river valleys, tender spinach, lettuce, arugula, radishes, salad turnips, and green onions, abundant rhubarb, and the first strawberries from southwestern Idaho late in the month. Greenhouse tomatoes and cucumbers appear early at some stands.
Stored Idaho potatoes and Treasure Valley onions still hold the table, and dried Palouse lentils and peas remain a staple. Bedding plants, herb starts, and tomato and pepper transplants crowd the market tables for home gardeners. Idaho value-added goods — honey, fresh-milled flour, hard cider, and wine — fill out the stand. Choose asparagus with firm, tight tips and snap it fresh, pick dry, fully red strawberries and refrigerate them unwashed in a single layer, and keep cutting greens cold and crisp.
Night Sky This Month
May offers warm, comfortable nights for Idaho stargazing, though the darkness shortens toward summer. The Central Idaho Dark Sky Reserve — the Sawtooths, Stanley Basin, and Sun Valley, the first such reserve in the U.S. — is fully accessible now, and Bruneau Dunes State Park south of the Snake runs its busy spring-into-summer observatory programs. The high desert of the Snake River Plain and the wide Lost River and Pahsimeroi valleys give dark, transparent skies well away from the city glow.
The sky pivots toward summer: Leo sinks into the west, Boötes with brilliant Arcturus and the keystone of Hercules ride high, and the first stars of the Summer Triangle — Vega, then Deneb and Altair — climb the eastern sky late in the night. The Eta Aquariid meteor shower, debris from Halley's Comet, peaks around May 5–6 low in the predawn east. For this year's exact planet positions and meteor timing, see the printable Idaho night-sky guide.
Butterflies & Pollinators
May is a strong butterfly month across Idaho's low and mid country. The foothills, canyon grasslands, and river bottoms host Western Tiger and Anise Swallowtails, Sara Orangetips finishing their flight, Western Tailed-Blues and a parade of other blues, Spring and Becker's Whites, coppers, checkerspots, and the year's first fritillaries nectaring on the balsamroot, lupine, and blooming camas.
The sagebrush steppe and the Camas Prairie come alive with butterflies tracking the peak bloom, and Milbert's Tortoiseshells work the streamside nettle of the foothills. As the mid-elevation snow clears, the first mountain-meadow species emerge on the lower forest slopes. The high Sawtooth and Lost River basins are still melting and their alpine butterfly flight — parnassians, alpines, and high-country fritillaries — is a month or two off, but Idaho's lower elevations are now in full, varied flight.
Trees This Month
May puts Idaho's trees in full spring growth. The riverside black cottonwood begins to release its drifting cotton along the Snake, Boise, and Clearwater, the quaking aspen groves leaf fully across the foothills and mountain draws, and the native chokecherry, serviceberry, hawthorn, and Rocky Mountain maple flower and set fruit along the canyon edges. The state's syringa (Lewis's mock-orange) puts on buds for its June bloom.
In the forests the conifers flush bright new growth: ponderosa pine and Douglas-fir push soft candles and shed pollen on the lower slopes, the state tree western white pine candles in the north-Idaho panhandle, and the western larch wears its full soft-green spring needles among the dark redcedar and hemlock of the Clearwater and St. Joe country. Higher up, the Sawtooth and Lost River forests are only now greening as the snowline climbs toward the peaks.
Weather & Daylight
Across Idaho, a typical May day averages a high near 63°F and a low near 37°F, with about 2.3 inches of precipitation — statewide averages from the 1991–2020 U.S. climate normals.
Warmth builds fast into the 60s, mornings still crisp near 40, and rain showers freshen the air between sunny stretches.
| Average high | 63°F |
|---|---|
| Average low | 37°F |
| Precipitation | 2.3 in |
| Sunrise (mid-month) | 6:11 MT |
| Sunset (mid-month) | 20:59 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 Idaho's next month turns — what's arriving, blooming, and worth a night outside.
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Same month elsewhere: May in Illinois · May in Indiana · May in Iowa