How do you prune a lilac that has grown out of control?

April 4, 2023 Ask the Expert, Garden Design and Maintenance

Question:

I’m looking for help on how to best prune a lilac tree/bush that has grown out of control.

Answer:

Liz Stanley, Horticulture Community Education Assistant

For older common lilac stands (Syringa vulgaris) that need renovation, early spring is an excellent time of year to prune. Pruning when they’re still dormant means that you can see the form of the entire plant.

Start by using thinning cuts. This type of cut removes parts of the plant at its origin. (Try to avoid heading cuts which terminate the ends of branches.) Remove trunks and branches that are dead, damaged, crossing or unproductive, and weak suckers and watersprouts. When you remove these, the interior will be less crowded and the colony will be able to get more air and sunlight. Yes, some flowers will be sacrificed, but the plant’s health will improve. As you work, stand back and look to see if the overall shape is balanced. Remove trunks as close to the base as possible, leaving no unsightly stumps.

You can prune after the lilacs flower, but it’s much harder to see inside the interior if it’s a large lilac. Removing spent flowers makes the lilac look neater, but it probably doesn’t encourage more flowers for the next season.

Here’s our video on Pruning a Lilac Bush.

Here’s our video Pruning Woody Landscape Plants.