Trimming Lilac bush

Asked November 2, 2016, 2:28 PM EDT

We recently moved into an older home that has a lilac (tree) bush that is over 7 feet tall and at this time only has leaves at the top of the tree. Do I need to cut this back to bring blooms closer to the ground and if so how tall should it be? I am also unsure if it bloomed this past season. Thank you

Freeborn County Minnesota

1 Response

Congratulations on your new home! As you likely know, lilacs are early spring blooming shrubs - a favorite in MN. They develop the flower buds for next year soon after blooming, so pruning should take place within 2 weeks after blooming. Because the shrub is so large and you have not yet seen how it performs, you have some options:

- Leave it as-is, see how it blooms in 2017, and then prune it after it blooms.

- Remove about 1/3 of the largest branches / trunks now (called renewal pruning) with the understanding blooms will be few to none possibly next spring. This kind of pruning will prompt production of new, younger branches that will bloom in a couple of years.

- Cut the whole shrub down the ground (called rejuvenation pruning) with the understanding you will not see any blooms for a few years. However, this will prompt new growth and eliminate any large, trunk-like stems.

Here's an Extension publication on pruning trees and shrubs that will help explain more details and provide some diagrams: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/pruning-trees-shrubs/

To also prompt healthy growth / blooms, be sure the shrub is growing in full sun. If the shrub is shaded by large tree branches, you may want to do some judicious pruning of the tree to increase the amount of light. A lilac blooms best in full sun (6 hours minimum per day). If you find you need a professional arborist to tend to your trees or diagnose any issues, here is an Extension publication on how to hire a certified arborist: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/how-to-hire-a-professional-arborist/

Feel free to reply with additional questions.