How to Prune Your Lilacs in 7 Simple Steps

Perfectly shaped, full flowering lilacs are a thing of beauty in the landscape. And that’s certainly no accident. If left to their own devices, these spring-blooming, strong-scented members of the olive family will grow thick and wild. They will flower sparsely, and they will have crowded leggy stems. They won’t look like the lilacs pictured on the plant tags, or the ones you see on your neighborhood garden walk. And they’ll probably have issues with pests and disease.

The good news is, it doesn’t have to be that way. Your lilacs’ fates are in your hands, and in your gardener’s tool bucket. They just need to be pruned, promptly and properly! But, where do you start? If you’ve never pruned a lilac before, there’s a few quick tips you’ll want to be aware of before you start.

Lilac pruning really isn’t all that hard to do, it just takes a little patience! No matter the type of lilac you have, the same principles apply. Continue reading to find out exactly how to prune your lilacs, by following these 7 very simple steps!

Start Pruning With a Plan

Before you start lopping off random lilac branches, step back and take a minute to think about why you’re out there. Is it too tall? Too wide? Are they too leggy? Too dense? Have you been seeing fewer and fewer blooms each year? Is there evidence of disease or insect infestation? Would you like it to bloom again this year, if possible?

When it comes to pruning lilacs, you must begin with the end in mind. Each one of these issues will require a different approach and possibly a different technique. You should know what you want to achieve before you make a single pruning cut.

Gather Your Tools

Since lilacs are typically multi-stemmed with a dense branch structure, you’ll want to protect your eyes with some work goggles, or sunglasses at the very least. If you spread a tarp around your lilac’s base, it’ll catch little sticks and branches that fall during the process, making cleanup a little easier.

Depending on what variety you’re working with, you might be able to perform basic pruning tasks with a small hand tool, but you’ll likely need a little more power if you’re dealing with large stems or branches. Here are the most common lilac pruning tools and their usage:

Before you start working, make sure your tools are all clean and sharp. Ethanol or isopropyl can be used to quickly remove pathogens from blades. Or use a solution of 9 parts water to 1 part bleach to disinfect tools that have been used on other plants in the yard.

Have your local hardware store sharpen anything that’s not going to produce neat, perfect cuts, and always keep tools oiled and stored in a dry location.

Prune at The Right Time

Generally speaking, ‘prune immediately after flowering’ is the golden rule of lilac maintenance. As a spring flowering shrub, lilacs set their blooms in mid to late summer for the following year. If you prune in fall or early spring, you’ll be removing some or all of its buds and you will not get the spectacular flower display you’re anticipating. 

So get out there as soon as your lilac’s flowers have faded, and start doing the prep work for next year’s show. A gardener is nothing if not optimistic.

There are exceptions to the rule, of course. If you’re looking to restore an old, tired, overgrown lilac by cutting it completely to the ground (see rejuvenation pruning below), you should perform these cuts in late fall or early winter when your lilac is dormant. This will cause less stress and reduce its vulnerability to pests and diseases.

Reblooming lilac varieties provide another exception to the ‘prune immediately after flowering’ rule. Most flowers in this category are sold under the brand name ‘Bloomerang’ (Syringa x ‘Penda’) and they are designed to send up a second bloom in midsummer.

While you will want to deadhead the spent flowers on these cultivars to encourage another wave, major pruning efforts should be performed later in the summer after these varieties are completely done for the season.

Remove Suckers

Lilacs are notorious for sending up basal roots, also known as ‘suckers.’ These shoots are a plant’s natural attempt to spread out and colonize an area. You will typically see them popping up out of the dirt near your lilac’s trunk or base.

If left alone to do their thing, suckers will draw energy from the roots and can hinder healthy growth and bloom production, so they should be removed. Dig down as close to the root base as possible and cut them out with a lopper or bypass pruner. Repeat each year as part of your maintenance routine.

Make Cuts To Reduce Density

Considered routine maintenance in most lilac shrubs, ‘renewal pruning’ involves cutting out roughly ⅓ of existing stems at the base. Begin with the oldest and tallest stems as well as those that are dead, crossing, or broken. Look for the thickest, woodiest stems to determine the oldest. They will usually be gray and have significantly fewer branches and leaves than newer growth.

Sometimes called ‘thinning,’ this technique will open up your lilac’s center, which will allow more sunlight to reach inner leaves, allow more water to reach roots, and encourage proper air circulation. It’s a good technique for managing fungal disease, increasing bloom production, and keeping shrubs at their optimal size.

Make Cuts to Reduce Height

Since many lilac species will grow fast and furiously, height reduction is often a lilac pruning goal. While there are several ways to achieve this effect, some will yield a healthier, more attractive plant than others. Here’s a comparison of three common techniques:

Topping Off

If you see someone on your block take a hedge saw or power shears through the middle of lilac to make it shorter, this is called topping off. While the process may reduce your plant’s height immediately and relatively easily, it is not the technique of choice.

Pruning a shrub in this manner will encourage growth from the points just below your cuts, creating a broom-like effect with many smaller shoots at the top of a stump. Side growth below your cuts will be minimal, flowering will be limited, and future shape will be awkward.

Heading Back

Considerably more time-consuming but far more likely to yield desirable results, heading back involves reducing the length of individual branches to reduce overall height. Here’s how it’s done:

Rejuvenation

If your lilac is growing out of control, has gotten leggy, or has stopped blooming altogether, you can cut the entire plant down and encourage it to start over. This process should be done during your lilac’s dormant period, when it will not be stressed by the procedure. It is an exception to the ‘prune immediately after blooming’ lilac rule.

Before you begin, however, it’s important to note that your lilac will not be blooming again for a few years. This is a long-game strategy for restoring your lilac to its original glory and it requires patience. Here’s how you do it:

Make Cuts to Add Shape

It’s not uncommon to see a landscaper or homeowner tackle a lilac with hedge shears. The process is easy and can be very effective in achieving a wall-like screen. The problem is, this technique encourages bushy outer growth that will eventually reduce light and air to your lilac’s center. A dead zone with no leaves or flowers will form inside and you won’t be able to keep cutting your shrub back to the desired size.

In formal landscapes, where a more rigid structure is desired, shearing can be used to promote shape only if it is accompanied by some thinning or renewal cuts and followed up by a careful heading back. This process will not create a tight, perfect hedge but the effect can be similar, if a little more natural looking. And your lilac should still flower if cuts were made thoughtfully.