Pruning Common Lilac

Prune common lilac in June, immediately after flowering finishes. Lilacs bloom on the previous year's wood, so pruning later in summer or in winter will remove next spring's flower buds. The main goal is to maintain an open, balanced framework and encourage vigorous new growth that will carry next year's flowers. Use clean, sharp secateurs for stems up to pencil thickness and loppers or a pruning saw for older, thicker branches. Start by removing all spent flower heads just above the first pair of strong buds or shoots below the faded truss; this prevents the plant wasting energy on seed production. Next, cut out any dead, damaged, or crossing branches to improve air circulation and reduce disease pressure. Every few years, remove one or two of the oldest stems at ground level to rejuvenate the shrub and prevent it becoming congested and leggy. Aim to take out no more than a quarter of the total growth in any one year. If your lilac has become overgrown or neglected, you can renovate it more drastically by cutting the entire plant back to 50–60 cm above ground in June, though this means sacrificing flowers for a season or two while it regrows. Lilacs often produce suckers from the base, especially if grafted. Remove these promptly by tracing them back to the root and pulling or cutting them off cleanly; if left, they can overtake the named variety. Avoid shearing or formal clipping, which spoils the natural habit and reduces flowering.