Native Plants for Illinois

Roughly sixty percent of this state was tallgrass prairie when settlers arrived, something on the order of twenty-two million acres. What survives today is a fraction of one percent. It is one of the most complete conversions of a landscape anywhere in North America, and it happened because the same deep, black soil that grew big bluestem eight feet tall grows corn better than almost any ground on earth.

The practical consequence for a gardener is that the plants of this place are mostly gone from the places you can see them. Most Illinois residents have never stood in tallgrass prairie. Planting a few square yards of it is a small act of restoration in a way that is not true in states where the habitat still exists somewhere down the road.

Where the remnants survived, and what they teach

The surviving scraps are informative about siting. Prairie persisted in two unlikely places: old railroad rights-of-way, which were never plowed and were periodically burned by sparks, and pioneer cemeteries, which were fenced and left alone. If you want to know what belongs in your county, those two kinds of places are where to look, and many are now protected preserves.

The state is not uniform. North of a line roughly through Peoria, glacial till left the flat, rich, poorly drained ground of the Grand Prairie. The far northwest corner escaped the last glaciation and is hillier, with thinner soil. The southern tip, below the glacial limit, runs into the Shawnee Hills and a forest flora with southern affinities, including species that reach their northern edge there. Sand deposits along the Illinois and Kankakee rivers support a completely different, drought-adapted community.

Planting into black soil

Rich prairie soil is a mixed blessing in a garden. It grows everything well, including the weeds and the aggressive natives, so a small bed of prairie species in good ground needs more editing than the same bed in lean soil. Species like cup plant and Canada goldenrod will take over a tidy border. Choose the better-behaved prairie plants for small spaces, and save the vigorous colonizers for a large area you are happy to let fill in.

Drainage is the other consideration. Much of the flat till plain was wet prairie before it was tiled, and low spots in yards still hold water in spring. That is an opportunity rather than a defect, because wet-prairie species are some of the best plants in the regional flora.

Confirming what is native to your county

The Illinois Native Plant Society has chapters across the state, and the Illinois Nature Preserves Commission protects remnants in most counties. In the Chicago region, a long-running coalition of conservation organizations maintains extensive guidance on locally native species and where to buy them.

Sources: Illinois Department of Natural Resources (natural divisions and prairie remnants); Illinois Natural History Survey, University of Illinois (vegetation and species distribution); USDA PLANTS Database (native status by state).