I have two Sourwood trees growing. They are about 20 ft. high. Should I skirt them as they grow to the ground and I have noticed moss under them. I think they would look better trimmed. If so when should I prune the lower branches. I am in RI and above their natural habitat but they are doing great except for the base of the tree being full. They kind of look like Christmas trees now.
It is okay to remove the lowest branches. Keep it to less than 25% of the foliage, don't strip them up too high. You can do that at any time.
Here's an article with some more information on sourwood trees: