Asked June 29, 2020, 1:15 PM EDT

I have very 20 year old lilac bushes. They are very bare on the bottom half but full at the top - probably 20 feet tall. How far can I cut them back without killing them? What time of year would be best? Thank you!

Hennepin County Minnesota

3 Responses

If you trim them back now you won't get any blooms next spring as the buds are set. However, you may want to sacrifice one season's bloom to get them under control. I admit to having the same problem and cutting my lilacs back to about 5' tall a few years ago. What you can do now, should you decide not to trim the height back, is cut out the older, thick stems out down to the ground. That encourages new young growth. You can remove up to 1/3rd of these old stems at a time. This should be done whether you cut them back or not. Lilacs should be trimmed right after the blooms fade in the spring before they have a chance to develops the buds for the following year's blooms.

Thank you for your reply. I am willing to sacrifice one season of blooms. In actuality they can’t be 20’. Maybe more like 12’. It’s safe to cut them back to 5’? Should I wait until fall?

Go ahead and cut back now or wait until fall if it works better for you. Either way the blooms for next year will be gone.