Early spring is the time to prune shrubs that don't flower in the spring, or ones with insignificant blooms that you don't mind pruning off. Spring blooming shrubs such as forsythia and lilac should be pruned after they bloom. Diseased, damaged or dead branches are the first to go no matter what time of year. Plants such as dogwoods here in Colorado thrive on the rejuvenation pruning gives them because it stimulates new branch growth and the new red, or yellow depending on the variety, branches are what gives the shrub its interest and beauty. Pruning is also used in thinning and shaping a shrub or containing it in size. There are right and wrong ways to prune so if you're in doubt, get advice from an expert.
Recently I got to hear from an expert plantsman, Tom Throgmorton of Throgmorton Plant Management about these and other pruning tips. His excellent talk at Fort Collins Nursery was very informative and accessible. You can catch him again April 10 at the Shrub Pruning Workshop at the Gardens on Spring Creek, Fort Collins, Colorado www.fcgov.com/gardens. Go and learn!