The most universal answer is late winter, around February or March. This obviously doesn’t hold true for EVERYTHING, but it works as a general rule.

Why is now a good time to prune? All plants store starches in their tissues to survive the winter and begin growing again in the spring. Trimming excess limbs off in the fall would deprive the plant of some of its “back-up power.” Plants also start growing around this time. This will help hide any unsightly nubs that remain.