How to Prune a Lilac Bush for a Massive Amount of Fragrant Spring Blooms
Want to keep your lilac blooming its best? Follow these essential pruning guidelines for a full shrub and tons of flowers.
Liz Baessler
Learning how to prune a lilac bush is one of the keys to growing strong, healthy shrubs that look good and bloom every year. Lilacs aren't delicate or needy, but pruning them the right way is how you make them shine.
Lilacs are shrubs for all seasons. They're hardy, vigorous and intensely fragrant. Their blooms appear in late spring, generally in mid-May, and perfume the entire garden. Their height and foliage make them perfect for tall, flowering screens for summer and autumn.
To keep growing lilacs that look their best for many years to come, you need to prune them. Let's take a look at how and when to trim lilac bushes for beautiful, healthy shrubs that produce tons of blooms.
Do You Need to Prune Lilac Bushes?
Learning the basics of pruning is important to growing almost any shrub, but it's especially true for lilacs. These classic spring-blooming bushes require regular pruning to look their best. Lilacs are relatively fast growing shrubs, and if left to their own devices they can get leggy and sparse.
The lower branches of lilacs often get shaded out by upper growth, which makes the lower leaves fall off. The result is a top-heavy shrub with a thin looking bottom. This is fine if you want your lilac to take on more of a tree shape, but if you want it to be more of a classic, full shrub, you'll have to break out the pruners.
Pruning lilac bushes on a regular basis also keeps them from becoming too tall. 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. That's quite the size for something you probably planted as an accent plant next to your house!
When to Prune a Lilac Shrub
Want to know when to prune a lilac shrub? It's a good question. If your lilac is very young, it's best to let it fill out on its own for a few years – most lilacs don’t need pruning until they're about 6 to 8 feet (2-2.5 m) tall.
The best time for pruning lilacs is spring, immediately after flowers have faded. Don't wait until summer! Lilacs set next year's flowers on this season's growth. If you prune them too late, you'll be lopping off potential flowers. Pruning shrubs too late can kill young developing buds and it's one of the most common reasons why a lilac won't bloom.
If you're doing a light pruning or a hard rejuvenation pruning, just after flowering is still the right time to do it. 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, which we'll get into later. This kind of drastic pruning should be done in late winter. With renovation pruning you remove entire stems, so losing the flower buds becomes less important.
How to Prune a Lilac Bush
Many flowering shrubs bloom best on new growth, and lilacs are one of them. The older the branch, the fewer flowers it’s likely to produce. So pruning every year, even lightly, is an essential part of their annual maintenance if you want lots of blooms.
When pruning lilacs, heading back or just cutting the tops off of overgrown stems is often not enough. It’s generally better to cut the entire stem. Always trim lilacs with clean clippers. Remove spent blooms all the way to the stems to prevent seeding and encourage more blooms.
Cut back a third of the branches. Prune out any shoots growing near the ground that are 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 also be necessary.
Regular Maintenance Pruning
Annual pruning keeps lilacs healthy 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 you trim the lower branches, use thinning cuts to prune the bush. This type of 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
If you’ve inherited an overgrown shrub or just let yours become lanky, it may be time for rejuvenation pruning. You can do this 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.
You can also use this three-year plan for maintenance pruning. If you start when shrubs are young, simply continue the cycle every year. This will keep down the height of the shrub since the heaviest, thickest stems are also often the tallest ones. Gradually remove them to bring down the overall height of the shrub.
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 won't 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.
Lilac Pruning Essentials
