...Yarrow? I have four plants of it and they are very tall, not what I would call great low cover and they do not spread very much at all. I am wondering if you know of some kind of yarrow I am not aware of?...

Kat, I'm sure that there are low growing varieties that you can buy. We have some wild stuff that is growing in Ma in Law's garden It is very low and would be perfect. I can send you some if you like. or you can wait until it seeds and I could send seeds.

But I think most varieties would spread if they were mowed.