When should you prune lilacs?

A mature lilac plant should be pruned just after the flowers fade to avoid cutting off next season's buds, which bloom on the current stems, referred to as old wood. Avoid pruning new lilac plants until the bushes are 6 to 8 feet tall.

To prune a lilac bush, cut off dead wood, sucker shoots, the oldest canes and any canes that are thicker than 2 inches. Also, remove canes that cross one another to improve air flow around the bush, and trim remaining canes to eye-level. After pruning, a healthy lilac bush has eight to 12 canes that are 1 to 2 inches wide.