Fall Blooming.
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.
Check the pH of your soil.
Furthermore, is it OK to trim bushes in the fall? Do not prune by cutting those stems to the outside of the shape of the shrub. Jul 14, If you put off pruning until later in the season, you risk removing the developing buds.
This is equally true for lilacs such as Bloomerang Purple that bloom twice a year.
Prune as far back as you want right above the first leaf joints.
By pruning the bush after its initial bloom, you encourage new growth and more flowers in its second bloom in early fall. Why is it important to prune lilacs annually?Estimated Reading Time: 2 mins.