Ask the Experts: How and When to Prune Lilacs

Here's a garden expert's advice on how and when you should prune lilacs to enjoy spring flowers. Also learn why your lilacs are not blooming.

when to prune lilacsCourtesy Jean Owens
Eastern tiger swallowtail butterfly on a lilac bush

Lilacs are popular shrubs for their fragrant colorful blooms. Many gardeners wonder exactly how and when to prune lilacs. Ken Kuhnen of Machesney Park, Illinois, wrote in asking, “My lilac tree is beautifully shaped, but I need it to be smaller. Where do I start?”

When to Prune Lilacs

With any type of lilac, you should only prune branches right after the flowers fade to enjoy maximum spring color the next year. New lilac buds from on old wood. So if you start snipping in summer, fall or in spring before they bloom, you’ll cut off the forming buds and the plant will not bloom.

Note that different perennials have different pruning needs. See our quick guide on when to prune shrubs for all the details.

How to Prune Lilacs

To make your plant a little shorter, remove several of the larger stems to ground level. This will encourage new growth at the base of the plant. Reduce the height by no more than a fourth of the plant each year.

Here’s exactly how you should do it. Make cuts above an outward-facing branch or healthy buds. Repeat this process over the next few years and you will have a shorter plant with greenery from the tip of the stem to ground level. Cutting the whole plant back to the ground can result in a larger plant than you started with, and that means even more pruning to achieve your desired results.

Here’s more tips on how to prune like a garden pro.

lilac shrubCourtesy Sherrell Koski
Lilac flowering in spring

Why Is My Lilac Not Blooming?

“I was given a small lilac bush years ago from a friend’s garden. Every spring I’m so disappointed to see no flowers. Why is my lilac not blooming?” asks Georgette Jahn of Dingmans Ferry, Pennsylvania.

Shade and improper pruning can prevent lilacs from flowering. Lilacs flower best with at least six hours of direct sunlight. Consider moving the bush to a sunnier location. Too much high-nitrogen fertilizer and improper pruning can also result in a lack of flowers. Go easy on the fertilizing, and prune only if needed right after the lilacs should have bloomed. These plants develop their flower buds in the summer, and the buds open the following spring.

Do you really love lilacs, but wish they bloomed longer? Check out the new reblooming lilac options out there, like Bloomerang Purple from Proven Winners.

Next, learn when to prune hydrangeas for big, showy blooms.

Melinda Myers
Nationally known gardening expert, TV/radio host, author, columnist and speaker.