Always prune lilacs after they are finished blooming, never before, for best blooms next year.
The best time to prune lilacs is right after they finish blooming in late spring or early summer, usually in June in our area. Prune annually to maintain a good shape, support good health, and facilitate abundant blooms next year
Warning: if you wait until late summer or fall to cut spent blooms or cut back the plant, you'll remove the buds for next season's flowers, which is why this time of year is crucial for pruning lilacs.
Why?
Lilacs form next year’s flower buds shortly after blooming, so pruning too early or late in the season can remove those buds and reduce blooms for the following year.
Quick Tips
- Remove spent blooms to encourage more energy into growth.
- Cut back up to 1/3 of old stems to maintain shape and air flow.
- Avoid heavy pruning in fall or early spring—it can limit flowering.
- Cut out suckers before they take over the main plant. This more vigorous pruning helps to rejuvenate the plant overall.