Hello, I am not totally new to this site, I have been reading and leaning alot from this website for over a year now. But I am new to asking questions. I have a man made hill facing the East covered with Ajuga. I put it mainly there to keep the hill from washing away. I put in 21 flats two years ago, it was spreading very well, even through the woodchips I had to put down. There is no shade, except on 1/4 of it, up near the garage at the later part of the day. But I do have undergrownd sprinkling on it. The problem is, it is not returning this year. It is very sparse. I put Preen down last year, did I kill it with that? Or is it short lived? Or is it to hot? I live in Northern Michigan, so not likely!