The best time to prune all evergreens is in the spring as they develop new growth. Be aware, though, that if you prune too far back on the branch, evergreens won't regrow. Unlike deciduous plants that will resprout behind your cut, an evergreen will not develop new growth. If the area has no growth now, it never will. That's why it's important to prune evergreens as they grow, not after they get too big. If you cut back to an area with no growth, you'll just create a big dead spot on the tree.