Fortunately, rejuvenation pruning can revive an old lilac in about three years'.

Jun 17, The lilac may benefit from pruning using the"1/3 method". which is to remove one third of the mature stems to their point of origination each year for the next three years (thereby rejuvenating the entire plant). Afterwards you remove one or two mature stems each season to maintain size and shape. 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.