As soon as the lilac bush's flowers are dead, trim each flower stem back to the leaves, removing all trace of the flowers. This step stops the lilac from using its energy to make seeds. May 20, When to Prune Lilacs.
New lilac bushes don't require maintenance pruning until they are about 6 - 8' tall. The time to prune mature lilac plants is just after the flowers have faded. They set the next season's flower buds almost immediately, so late pruning will mean sacrificing next year's flowers. Jul 08, The time to prune mature lilac plants is just after the flowers have faded in the spring. Lilacs set next season's flower buds almost immediately, so late pruning will mean sacrificing the next year's flowers.
Pruning early also gives new shoots more time and energy to develop, ensuring plenty of blooms for the following spring.
Nov 03, When is the best time to prune my lilac bush and how do I do it? Answer this question + 3. Answered 5 answers Janice Hale on Nov 03, What I have been told is they should be trimmed within two weeks after they stop blooming. They may not. Timing is the Decisive Factor in Pruning Lilacs If you want to have your blooms next year, it is crucial to prune in those first few weeks after blooming ends. Ideally, this is when you would do maintenance pruning each year.