Talk to your state's DNR, and find out what grasses are native to the area you're dealing with. You're at least on the edge of the prairie, so there are classic prairie genera and species which will take care of themselves. If you live in an area which allows it, an occasional burn-off..every few years, will help maintain the health of the patch, but you can get along without it.

The state may even have a restoration program which could provide you with seedlings of native grasses.

to add to what donn said..I would recommend this website...Grow Native, a joint program of the Missouri Depratments of Conservation and Agriculture...

Here is a link that might be useful: Grow Native