When should I prune spring-flowering shrubs like lilacs and azaleas?

Prune them right after they finish flowering. Spring-flowering shrubs set next year’s flower buds almost immediately after blooming, so waiting until summer or fall cuts off next spring’s display. For lilacs, cut out dead wood and suckers, thin old stems at ground level, and optionally deadhead. For azaleas, snip dead flowers and remove dead or crossed branches, shaping only now. Don’t prune these in fall—that’s for summer-bloomers.