I hope it goes well, but would encourage you to add organic matter to the surface of your soil, never sand under the surface. Digging a bowl-shape in clay & filling with sand is a method for drowning roots, not improving drainage. And clay + sand = concrete. Over time, adding organic matter to the surface will support microbial life which will "do their thing" to dramatically improve drainage, fertility, tilth, all of the aspects of healthy, easy-to-work-with soil.

http://permaculturenews.org/2013/09/20/soil-not-dirt-dr-elaine-ingham-talks-soil-microbiology/

Thank you. I've read that before, but it doesn't seem to apply in the case of prairie soil. I've had good luck with the sand method and so far and the gaura looks great. For some reason, when I've done this in the past, the sand will incorporate with the clay and you won't even be able to tell sand was added in a few years. I guess the worms and ants do their thing to mix them together. I do mulch all of my flower beds with pine straw. I've been in the house for 15 years now and I've been able to get hydrangeas to grow in this clay. Right now, my biggest obstacle is keeping everything watered. We aren't getting much rain right now. The big test will be to see if the gaura survives the winter. Oddly, the prunella, which was suppose to be easier to grow, is struggling in the pot I put it in with Miracle Grow moisture retentive potting soil (blue bag). Go figure. Still, they were both cheap experiments and I love a bargain.