I got a few arbor vitae trees at Home Depot, and they seem to be struggling. The foliage closest to the ground is dying and turning brown. Are they just too dry? What could be the problem? I actually planted two in the middle of August, when we were having a big dry spell. One did ok, but one came from the store with some brown on the bottom already, and within a month it was totally and completely dead and brown. I tried to keep it watered, but I know it was dry a fair amount of the time. So, I replaced that one with a new healthy looking one in the middle of September, and now the new one is starting to get brown on the bottom, too. It hasn't been too hot or dry, and all of my other plants are plenty healthy, including some young hostas I planted that same day in September, and they aren't getting any more water than the tree. Any ideas?