Early Spring flowers include Hepatica (look for it around April 15)
Followed by Dutchman's Breeches, Trout Lily, Spring Beauty (roughly the
third week in April)
then come Marsh Marigold and Trillium (around May 1)
followed closely by Mayapple and Dogwood.
Ladyslipper orchids bloom later (end of May) and, typically, in much wetter environments.
June brings Blue Flag (wild iris) and water lilies.
In late summer, prairie flowers bloom. Typical blooms in mid-July: Compass Plant, Bergamot, Black-eyed Susan, Purple Coneflower, Butterfly Milkweed.
Fringed Orchids bloom in late July.
August flowers include: Cardinal Flower, Woodland Sunflower, Goldenrod,
and New England Aster.
Wildflower Association of Michigan
The Virtual Herbarium
Michigan Nature Association
Michigan Botanical Club
Establishing and Maintaining a Prairie Garden (from U of Minnesota's Extension Service)
Planting Native Wildflowers
from Michigan's DNR
Sources for seeds and plants
Kalamazoo Nature Center holds a Native Plant Sale each Spring and Fall.
Grand Prairie Friends has a list of nurseries selling prairie plants and seeds.
Great Lakes Nursery
Other gardening Websites
Renegade Gardener : advice for the Northern Midwest