I have a 6' X 70' slope made up entirely of red clay. I am looking for a perennial groundcover that spreads quick, but also flowers ( the longer the better) and looks good in winter (coldest is 30 degrees). Also, where would I plant: near the top of the hill so it spreads downward or in the middle to spread both ways. We had thought about wintercreeper and carpet phlox, but have heard mixed reviews. Any tips or ideas would be greatly appreciated!