Here's a garden expert's advice on how and when you should prune lilac bushes to enjoy fragrant spring flowers.
How and When to Prune Your Lilac Bush
Updated on Jan. 23, 2025
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Proper Time to Prune Lilacs
Lilacs are popular flowering shrubs for their fragrant colorful blooms. Many gardeners wonder exactly how and when to prune lilacs. Birds & Blooms reader 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?”
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.
Key takeaway: Spring-flowering shrubs and trees like forsythia, lilac, quince, bigleaf hydrangea, rhododendron and azalea, form their flower buds on wood from the previous year. These are best pruned after flowering in spring.
Reduce Lilac Bush Size
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.
Note that different perennials have different pruning needs. See our quick guide on when to prune trees and shrubs for all the details.
Reblooming Lilacs
Do you really love lilacs, but wish they bloomed longer? Check out the new reblooming lilac options out there, like Bloomerang Dark Purple from Proven Winners.
Next, learn when to prune hydrangeas.
