If they have boxwood blight, root rot, mineral deficiency or another health issue cutting them back isn't going to accomplish anything. Otherwise any printed pruning manual or comparable web pages will suggest optimal pruning times for this and other kinds of cultivated trees and shrubs - if you are estate gardening you should become familiar with such resources.

Here is a link that might be useful: About Boxwood

This post was edited by bboy on Sat, Jan 17, 15 at 13:34