Apr 02, Most lilacs don’t require pruning until they reach about 6 to 8 feet ( m.) tall. The best time for pruning lilac bushes is right after their flowering has ceased. This allows new shoots plenty of time to develop the next season of blooms. Pruning lilacs too late can kill young developing buds.
If you are pruning lilac trees or shrubs entirely to within inches of the ground, it is best to do so in early spring. Jul 08, When to Prune Lilac Bushes. Many of the newer lilac varieties grow quickly and might need pruning starting in their second or third year.
In general, by the time a stem reaches more than 2 inches in diameter, it should be pruned. If you are diligent with annual pruning of your lilac, the shrub will grow to about 8 feet tall with flowers throughout the branches. A lilac bush does best when it is trimmed every year. Doing so helps to maintain the plant's shape and to minimize the number of old, damaged branches, which are vulnerable to disease.