I don't have clay soil, but I did stay in a Holiday Inn Express last night.

Most of the big beautiful graceful, warm-season deciduous grasses you covet don't care much about the quality of the soil, but they do care about drainage.

You'll either have to pre-prepare large planting areas/beds, or use pocket planting techniques. Both methods are the same, and differ only in scale.

Dig out a hole, at least twice as wide and deep as the rootball of the plant you are installing. Mix the clay in thirds, with coarse sand and organic material. Fill the bottom with the mix, and install the plant, backfilling with the mix.

There is actually a good deal of difference between widespread amending of clay soil and preparing individual planting holes. Regardless of the size of the planting hole, if working with heavy clay soil, amending and loosening the soil within the planting hole simply creates an area of loose, perhaps well-draining soil within the confines of the poorly draining clay soil. In effect you have created a bucket or bathtub that will hold the water and not provide drainage.

If amending and loosening the soil over a widespread area is not possible or convenient, create a very shallow, wide hole in the clay - very dish-shaped - plant high and mound better soil upto the root crown. This will still allow adequate drainage and give the plant roots sufficient anchor. Plant roots are very tenacious and they will penetrate into the clay. Actually, the work of plant roots breaking up clay soil is a rather efficient way of loosening heavy soils but it is a slow process.

I live near a wetlands with clay soil and have been using specially prepared planting holes. Since everything drains toward the wetlands, I have no standing water over my ornamental grass beds during heavy rains. All of my ornamental grasses are thriving. I typically dig a hole 18" to 30" in diameter and 14" to 24" deep. I mix peat moss and composted manure with the native soil to make a loose organically nuturing planting hole. Regarding fertilizer, I like to add a little triple phosphate and slow release 12-12-12 capsules to the bottom and outer walls of the planting hole to encourage the roots to stretch deep and outward. The ornamental grasses send roots throughout these planting holes much faster than through the native soil, although the roots will spread through the surrounding clay soil in time. Clay has slow drainage, but holds nutrients well. I can go farther between occasional waterings. I can not use raised mounds without creating a lump of dirt that drys up without consistent watering and kills surface layer roots. I would suggest preparing the proverbial $10 hole for a $1 pot of ornamental grass this summer and see for yourself that ornamental grasses are far easier to grow than one might suppose. Be sure to pick a spot with lots of sunlight! Also remember if getting small pots of ornamental grass that the perennial saying applies in regards to each of three years growth in "One to sleep, One to creep, and One to leap!" This basically means that you will enjoy your grasses with the plants gaining maturity each year. Some grasses will grow slower or faster. With the amount of ground you seem to have, you should have plenty of room to play!

sounds like you're in michigan, although i didn't know that MI was clayish.

Anyway, Miscanthus grows well in solid clay--maybe too well! many are invasive, get too big and are hard to eradicate. you might try a smaller cultivar like 'yakushima dwarf' or 'little kitten', or a less invasive species of miscanthus. If you like tall, miscanthus giganteum(?) is reported to be non-invasive.

Pennisetums also do well. As for native grasses, Panicum does very well in clay, and is available in dozens of cultivars for varieties sake. i've tried Sporobolus, and it does tolerably well.

You might contact a mail-order company called 'Prairie Nursery' in WI. They sell a wide variety of prairie perennials as well as grasses, and have special blends specifically for busting clay soil. i'm sure they would be glad to help you. their website has detailed info on starting a prairie.

for more info on grasses, rick darke has a great book out now. you can probably get it for $30 or so on web. good luck.