Lilac Pruning Guide: How To Prune A Lilac Bush

Lilac pruning is rewarding because pruning lilac bushes means their fragrant flowers will thrive and flourish the next year. Learn how to prune lilacs to either maintain them or to tame them.

Pruning Of Lilac Bushes
prune lilac
(Image credit: JensGade)

Tips For Pruning A Lilac – When & How To Prune Lilacs

Lilacs are shrubs for all seasons, hardy, vigorous and intensely fragrant. Their blooms appear in late spring - generally mid-May, scenting the entire garden. Their height and foliage make them perfect for tall, flowering screens for summer and autumn. 

While lilacs lose their foliage in fall, their appealing branching pattern lends interest to a winter garden. Periodic pruning is vital to keep lilacs healthy and looking their best. Although there are smaller varieties that grow from 10 to 15 feet (3-4.5 m) tall, many lilacs can reach heights of about 30 feet (9 m) tall without regular pruning. 

Pruning lilac trees on a regular basis keeps them from becoming too tall and unmanageable.

Lilacs are not delicate or needy, but lilac pruning is important. If you are wondering when and how to prune a lilac bush, we have outlined it for you in this article. 

When to Trim Lilac Bushes

You may be wondering when to prune lilacs. Most lilacs don’t require pruning until they reach about 6 to 8 feet (2-2.5 m) tall. The best time for pruning a lilac is when its flowers have finished and have faded. Don’t wait until summer or fall but instead prune them when they have finished blooming in late spring. This allows new shoots plenty of time to develop the next season of blooms. Pruning lilacs too late can kill young developing buds.

Even if you want to simply do a light pruning, don’t wait until the lilac goes dormant. If you are pruning lilac trees or shrubs to within inches of the ground, it is also best to do so in early spring. New shoots will develop during the regular growing season as long as there are a few healthy shoots left. Once the growing season has ended, remove any unsightly shoots.

The exception to this rule is when you use the three-year rejuvenation or renovation pruning plan described later in this article. This kind of drastic pruning should be done in late winter. With renovation pruning you will be removing entire stems, so losing the flower buds becomes less important. 

How to Prune Lilacs

Many flowering shrubs bloom best on newer growth, and lilacs are among them. The older the lilac bush branch, the fewer flowers it’s likely to produce. So, pruning lilac bushes is an essential part of their annual maintenance, which includes deadheading spent flowers and regular maintenance pruning.

When pruning lilacs, cutting back the tops of overgrown stems is often not enough. It’s generally better to cut the entire stem. Trimming lilacs is best accomplished using clean clippers. Remove spent blooms all the way to the stems to prevent seeding and encourage more blooms later on. 

Cut back about a third of the branches. Cut away shoots growing near the ground that may be sprouting from the main trunk. In order to improve air circulation or to allow more light to filter through, trimming lilacs within the inner branches may be necessary. 

If you’ve inherited an overgrown lilac or allowed your shrub to grow lanky, you may need to follow the special procedure for rejuvenation pruning described later in this article.

Regular Maintenance Pruning

Annual pruning will keep your lilacs vital and lovely. The idea is to remove one or two of the oldest stems near to the ground. Keep in mind that the shrub should have a fountain shape rather than having many stems on one side and few on the other. The look should be balanced with equal weight on either side. 

Once the lower branches are trimmed, thin the lilac bush. This type of lilac pruning starts at the top of the bush. Cut close to where one branch meets or crosses another to let light and air pass through. Cut out all dead or damaged stems. 

Rejuvenation Pruning

When your lilacs have been neglected, they need pruning and they need it fast. You can renew these overgrown bushes over three years and change them into vigorous, attractive plants. Think of this as a three-year pruning cycle. 

The first year, prune back the lilac shrub by cutting out one third of the largest, thickest stems. Cut these in late winter or early spring, making the cut close to the ground. Take the time to trim out any dead or unhealthy branches. The second winter, remove another one-third of the stems. The third year, trim back the final third of thick branches. 

This three-year plan can also be used for maintenance pruning. If this is started when the shrubs are young, it can continue, year after year, for the rest of its life. This also keeps down the height of the shrub since the heaviest, thickest stems are also often the tallest parts of the shrub, so gradually removing them will bring the overall height of the shrub down. 

Renovation Pruning

Here’s a more drastic way to renovate an overgrown lilac shrub. Renovation pruning means cutting the entire bush back significantly. This should be done in late winter. Make the stem cuts some 6-8 inches (15-20 cm) off the ground. 

While you will not have flowers during that growing season, many shoots will develop after this pruning. The following winter you can select a handful of the strongest shoots to provide a new framework for the old shrub. 

Nikki Tilley
Senior Editor

Nikki Tilley has been gardening for nearly three decades. The former Senior Editor and Archivist of Gardening Know How, Nikki has also authored six gardening books.