How do I know what month to prune my Rose of Sharon?

Barb
by Barb

my rose of Sharon is about 5 yrs old and growing more into a tree than a bush. Is it ok to prune it back, and in upstate New York what time of year do I do this? How far back can I prune it so it will sprout into a more bush-like plant rather than now more of a trunk with branches and a few flowers when it blooms. Thanks!