I picked up a job doing a reinstall on some beds. While I was ripping all the old stuff out, I noticed the ground is rock solid, clay. There were a lot of lilies, a few cottoneasters, potentilla, and some perennials. I have to install: Sweetspire Phlox Rhododendron Hydrangea Spirea gold thread cypress euonymus Columbine Lamium Aubertia Delosperma Im just trying to figure out what I need to add to the soil to make it workable. I was going to attempt to till it up, the top layer anyway, then add maybe some coarse sand, and some bagged compost mix. Any suggestions what to do with this? thanks.