Iowa Nature Guide: May 2026
May is peak migration and peak greening in Iowa — the warbler waves crest, grassland birds return to sing over the prairie, the woodland canopy closes, and the frost-free date finally arrives so the warm-season garden can go in. It is one of the richest and busiest months of the Iowa nature year.
What to look for this week
- Feeders are at their winter peak — chickadees, nuthatches, and cardinals work the seed, while wintering bald eagles already crowd the open water below the Mississippi dams at Keokuk and Le Claire.
- The Quadrantid meteor shower peaks in a short, sharp burst around January 3; watch the northeast after midnight from a dark site like the Loess Hills ridges.
- A planning week — order seeds early and favor the short-season varieties that finish reliably in northern Iowa's cold.
Birds This Month
May is the climax of spring migration and the best month for songbirds in Iowa. The warbler waves crest in the first half of the month, when wooded river corridors and parks fill with yellow, chestnut-sided, magnolia, blackburnian, and a dozen more species moving through the fresh canopy. Baltimore and orchard orioles, rose-breasted grosbeaks, indigo buntings, scarlet tanagers, and ruby-throated hummingbirds all arrive to nest, and the dawn chorus reaches its fullest pitch.
On the prairie and in the hayfields, the grassland breeders return and set up: bobolinks bubbling over the meadows, dickcissels buzzing from fence wires, eastern and western meadowlarks singing, grasshopper and Henslow's sparrows, and sedge wrens. Neal Smith NWR and the Loess Hills prairies are alive with song.
This month's tip: early to mid-May at first light in a riverside woodland is the single best birding of the Iowa year — a strong overnight flight can drop dozens of warbler species into the new leaves.
What's Blooming
May moves Iowa's bloom from the woodland to the prairie. As the canopy closes, the last spring ephemerals — large-flowered trillium, wild geranium, jack-in-the-pulpit, mayapple, and Solomon's seal — finish on the forest floor. Out on the grassland, the prairie's spring flowers take over: the rose-pink nodding shooting star, golden hoary puccoon and golden Alexanders, blue prairie spiderwort, wild lupine, and creamy wild indigo color the Loess Hills and prairie remnants.
The state flower, the wild prairie rose, begins its long bloom along roadsides and prairie edges late in the month. In yards and parks, lilacs, peonies, flowering crabapples, and the white drifts of wild plum and hawthorn fill the air with scent — the lushest, most flower-filled weeks of the Iowa year.
Garden This Month
May is when the warm-season Iowa garden finally goes in. Once the frost-free date passes — early May in the south, mid-May in the north — set out the heat-lovers: tomatoes, peppers, eggplant, squash, cucumbers, melons, and basil, and direct-sow beans, sweet corn, and more squash into warm soil. It is the great planting month, and a good week of work now sets up the whole summer harvest.
Keep the cool-season crops productive too: harvest spinach, lettuce, radishes, and the first peas, and succession-sow more lettuce in a shadier spot before summer heat makes it bolt. Mulch newly set transplants to hold moisture and suppress weeds, watch for cutworms and flea beetles on tender seedlings, and stay alert to the forecast — Iowa can still throw a frost into the second week of May, especially in low spots, so keep the row cover within reach.
Zone 4b (far north Iowa): wait for the frost to clear — the average last freeze comes in mid-May here. Harden off and set out tomatoes, peppers, and squash only after about the 15th, and keep cover handy for a late cold snap.
Zone 5a (central Iowa): the frost-free date arrives early in the month; after roughly May 5–10, plant tomatoes, peppers, beans, squash, cucumbers, and sweet corn, and keep succession-sowing greens before the heat builds.
Zone 5b (southern Iowa): safe to plant all warm-season crops early in May — get tomatoes, peppers, melons, sweet corn, and beans in, and begin harvesting spring lettuce, radishes, and the first peas.
What's at the Farmers Market
May fills out the Iowa market with the full spring harvest. Asparagus is at its peak and most abundant now, and rhubarb is in full supply. The leafy crops surge — spinach, leaf lettuce, arugula, mustard and other greens, green onions, radishes, and the first head lettuce — all crisp and tender from the cool weather. Fresh herbs like chives, cilantro, and dill appear.
This is also the big season for vegetable and flower transplants and bedding plants, as growers bring tomato, pepper, and herb starts and hanging baskets to market for home gardeners. Look for fresh eggs, honey, and morel-season foraged goods at some stands. Choose asparagus with tight tips, keep greens cold and use them within a few days, and trim and refrigerate rhubarb stalks, discarding the leaves.
Night Sky This Month
May's evening sky over Iowa is fully a spring one, with the winter stars gone and summer's not yet risen. Leo still rides high in the west, Virgo with blue-white Spica spans the south, and orange Arcturus in Boötes blazes nearly overhead — the brightest star of the spring sky. The Big Dipper rides high, and following its handle's arc leads down to these spring beacons.
Late in the evening, the keystone of Hercules climbs in the east, carrying the magnificent Great Globular Cluster (M13) — a faint fuzzy ball to the naked eye from dark skies and a glittering swarm of stars in a telescope. The shorter, warmer nights of late May make for comfortable observing from a dark prairie site like the Loess Hills ridges.
Exact planet positions change from year to year — the printable Iowa night-sky guide lists what's visible this month from your part of the state.
Butterflies & Pollinators
May brings Iowa's butterfly season into full swing. The first locally bred monarchs hatch from eggs laid on emerging milkweed by the females that arrived in late April, beginning the season's chain of summer generations. The big swallowtails are on the wing now — eastern tiger swallowtails sailing along timber edges and black swallowtails over prairie and garden — alongside cabbage whites, orange sulphurs, and spring azures. Pearl crescents and silvery checkerspots appear in sunny openings, and the first red admirals and painted ladies of the resident broods take over from the spring migrants. On high-quality prairie remnants in the Loess Hills and at Neal Smith NWR, the prairie specialists begin to emerge. Warm, sunny afternoons are best for watching, when butterflies nectar at wild geranium, golden Alexanders, and the first prairie blooms, and males patrol hilltops and sunlit clearings in search of mates.
Trees This Month
By May, Iowa's woodlands are fully leafed out and the canopy has closed, casting the spring-ephemeral floor into shade. The late-leafing trees finish last: the bur oak, black walnut, and shagbark hickory push out their new leaves and drooping flower catkins, completing the green. Eastern cottonwoods release their drifting cottony seed on the late-month wind along every river and ditch — the 'cotton' that gives the tree its name.
Flowering trees peak: the white drifts of wild plum, chokecherry, and hawthorn scent the timber edges, and ornamental crabapples color the towns. The black locust hangs heavy with fragrant white flower clusters late in the month, drawing bees. With the leaves fully out, the timber shifts into its summer rhythm of growth and shade.
Go deeper with the Iowa guides
The complete Iowa birding, native-plant, wildflower, and night-sky guides — or the whole year in one bundle.
Same month elsewhere: May in Kansas · May in Kentucky · May in Louisiana