All lilac bushes benefit from regular attention. The purpose of pruning a lilac is to shape the plant and increase bloom quality. This is all part of regular garden maintenance.

It normally consists of removing dead or diseased branches and shaping up the shrub. Occasionally, we prune to reduce size and renew the health of the bush.

Remove any dead or excess branches. Some suckering is to be expected. Remove excess shoots, keeping some new growth to renew the plant.

Springtime is Best

lilac flowers
Familiar lilac blooms with their memorable scent.

Like most spring blooming shrubs the best time to cut away branches is directly after the flowers bloom. Lilacs will begin to set buds for the following year, pruning after they finish flowering will encourage the strength of the plant to grow and set flower buds.

Lilacs will begin to set buds for the following year shortly after they finish blooming. This is why we prune immediately after flowering. All flowering branches removed after this window will diminish the flowers for the following year.

How To Prune

pruning a bush
Keep suckers out of your lilacs. Cut, leaving dark branches.

When too many shoots grow straight up from main branches or grow inwards, it is time to remove them. The goal is twofold: increase airflow within and the overall shape and appearance.

Remove new growth flush with the bark, older branches around a collar of where it joins into another branch. Generally cut at an angle with sharp blades which leave a clean cut.

I use pruners and loppers when shaping my shrubs

For most shaping a hand pruner works well. I grub off very small growth along the main branches with my hand. Most large branches can be taken off with loppers

Basic how-to and good demonstration of tools.

Renew an Old Lilac

If you have very old lilacs which are looking poorly, pruning the entire plant down to about 1.5 to 2 feet will renew it.

I did this with the original ancient shrub growing in my front yard. Old branches riddled with borer, and a lost center meant it needed help.

Thus, cut all the way back like this, it soon grew to its large proportions with lots of blooms. While drastic, this method will greatly improve the health of an ailing bush.

Summary

  • It is a good idea to remove spent flowers, to encourage flower buds for the following year.
  • Remove suckers and small shoots at ground level. Leave a few shoots for new growth.
  • Clean out stalks that grow straight upwards and those that crowd the inside of the bush.
  • Trim back awkward branches and those which mar the shape of the overall shrub.
  • That’s it for regular maintenance pruning. Very old shrubs may need renewal.