Apr 02, Most lilacs don’t require pruning until they reach about 6 to 8 feet ( m.) tall. The best time for pruning lilac bushes is right after their flowering has ceased. This allows new shoots plenty of time to develop the next season of blooms. Pruning lilacs too late can kill young developing buds. 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, In general, by the time a stem reaches more than 2 inches in diameter, it should be pruned.
If you are diligent with annual pruning of your lilac, the shrub will grow to about 8 feet tall with flowers throughout the branches. The time to prune mature lilac plants is just after the flowers have faded in the spring. The best time to prune lilac bushes is after they bloom. They flower on last years growth. Wait for others to chime in, but i would pick out a third of the trunks and, after the flowers are spent, cut them to the ground.
The next year do the same with half of the remaining old trunks and take out the remaining trunks in three years. It is also a cultivar of Manchurian lilac, which is significantly different in form, habit and flowering than the common lilac.
jea32, I'd wait until after flowering in spring. While I'd not hesitate to do rejuvenation pruning on a typical common lilac now, one that is grown in a tree form (single trunk rather than multiple stems/canes from the ground) should be treated a bit differently.
Aug 27, Pruning off damaged branches could prevent further damage. Monitor next spring as lilac starts blooming for the adults and set traps using pheromones (see Lilac borer). Sprays can be applied.
Contact a certified arborist for treatment. If you believe the damage is likely caused by a pathogen, submit a sample to the UMN Plant Disease Clinic.