What month do you prune lilac bushes? 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.
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. Jul 08, Start by taking out the thickest stems first. Although you'll be losing some flowers for the current year, pruning overgrown lilacs is easiest early in the spring before the branches leaf out.
After three consecutive years of pruning your overgrown lilac.