May 20, 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. Jun 19, Knowing when to trim older lilac bushes is important. Most lilacs don’t require pruning until they reach about 6 to 8 feet tall.
The best time for pruning older lilac bushes is right after their flowering has ceased. This allows new shoots time to develop the next season of blooms. Pruning too late can kill young developing treeleaning.buzzted Reading Time: 3 mins.
If you trim a lilac bush too late in the year, then you’ll cut off unwanted branches and next year’s blossoms. The ideal time to prune is just after the bush finishes blooming for the year.