When to Prune Lilacs

The number of outdoor tasks is quickly shrinking. As I look out my kitchen window these days, there isn’t much left, at least not what there was just a month ago. From one gardener to another, don’t fret. Everything will come back: that’s the beauty of gardening.

There have been a few questions about lilac trees and what to do with them in the fall. Here’s a quick guide.

Lilac Biology

A little bit of biology background never hurt and in the case of the lilac, is extremely important. A lilac tree produces flowers in the spring – usually late May but this will depend on the type of lilac and your specific area.

The flowers of the lilac are short-lived, lasting approximately 2 weeks. Once the flowers have finished, next year’s buds set in soon after.

When to Prune

Because lilacs set next year’s blooms on this year’s wood, you must prune right after the flowers have died back. That way the summer growth will continue and the buds can set uninterrupted.

How to Prune

If you have an old tree: you can do some pretty heavy pruning and it will explode back in 1-2 years as if you did nothing to it. Alternatively, you cut it back by about a third. The result will be pretty much the same but this option is a little more work.

If you have a younger tree: one that just needs a bit of trimming to keep a certain shape or to keep it from producing too much shade where you don’t want it, simply prune out the branches you don’t want. Remove the suckers that grow low to the ground. Don’t prune too soon – wait until it is well established.

Remove dead branches and thin, spindly growth. Keep the tree fairly open to allow good light and air flow through. Some suggest that removing stems thicker than 2″ is the best way to choose which branches stay and which will go.

As with anything, use discretion. Regular pruning (after blooms are spent) will keep your tree healthy and blooming year after year.