Lilacs need to be pruned within two weeks of the flowers fading. If you prune them in the summer or the fall or early spring, you are cutting the flower buds off for next year. You also want to continually rejuvenate your lilac by cutting the oldest thickest stems back to the ground. We don’t ever want to remove more than a third of the entire plants live wood or else the plant will not produce flowers for three more years. Many lilac shrubs have 30 or 40 stems, which is way too many. Each plant