I have three Stephenson Hollies, of the tree shaped variety, planted a couple of years ago for privacy. I have never trimmed them. The branches are getting long and and the ends full of berries - and weighing the branches down. I want to trim it without hurting the trees. There's virtually no growth on the branches past the loaded down ends. . . and they produce beautiful red berries. Help!!! PS - nearby is a male, very tall compact tree holly, and on the other side are six treeform hollies.
Hollies can be pruned back by a third of their growth. Any more than that will likely harm the plants. This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm