I have a 100 + foot hedge of arborvitae across the back of my yard, a privacy hedge. The plants are about 20 years old and 15 feet high. I have noticed that the lower sections are starting to get male pattern baldness of a sort, they are getting thin. I need the botanical equivalent of a comb-over. Will they bush out in the lower sections if I top them? I had them pruned once where the person hedge trimmed the front of the lower section and it took some time for it to recover and did not improve them.