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A few years ago, when I went to grab the hose, I noticed a ton of branches had been torn off my lilac bush. I accused my poor husband of getting overzealous with the pruners. However, I soon discovered that the hack job was the work of a mother squirrel that was meticulously building her nest. She’d rip off a branch or two and then run to my chimney (that’s a whole other story). I was worried about the lilac coming back the following spring, but it has been flourishing. Lilac is among my favourite spring scents—when I work outside on my deck, I take deep breaths when they’re in bloom, as they sway in the breeze. When those fragrant blooms fade, it’s a good time for pruning lilacs. So I thought I’d share a few tips!
The perfect time to prune a lilac bush is after the flowers have bloomed and faded. Spring-blooming shrubs should be pruned right after they have bloomed. If you save the task for later in the season, you risk pruning off next year’s blooms (because next year’s flower buds form on the current year’s wood)—a mistake I made in the past with an unruly forsythia!
Tips for pruning lilacs
There are three maintenance tasks I need to cross off my lilac to-do list in the spring. I need to trim the dead blooms off, prune the shrubs, and cut out suckers that have popped up underneath. Most of the stems I’m dealing with are thin enough that I can use my hand pruners, but if stems are thicker, you may want to use a pair of bypass loppers. Make sure the blades are clean before you cut. And while the plant is blooming, use the same sharp pruners to snip bouquets. You don’t want to tear or snap off blooms, as this could harm the lilac bush.
Be sure to use sharp hand pruners to trim a lilac bouquet.
Trimming off lilac flowers
Removing the dead flowers from your lilac bush will encourage more blooms the following year. The important thing when trimming off your flowers is that you simply cut off the spent flowers—don’t worry about any surrounding stems. If you can see next year’s blooms forming (two new shoots coming from the stem), simply focus on the spent bloom’s stem. You don’t want to cut off next year’s flowers!
To deadhead lilacs, simply snip the dead flower, leaving the stem and leaves in place. If you see next year’s growth, leave it be.
Now with my dwarf Bloomerang, I want to encourage a second blooming, which should take place towards the end of the summer or early fall. Pruning off the spent spring blooms will encourage more new growth and more blooms for that second bloom time. I could also add a light dose of fertilizer that’s been formulated for woody plants, which will also encourage the shrub to bloom again.
My dwarf Bloomerang in bloom! Cut spent flowers after the spring bloom period to encourage a second growth of flowers in the fall.
Pruning lilac shrubs
A good rule of thumb when pruning lilacs is not to prune more than one third of a shrub’s stems per year. When one of my lilacs climbed a little too high towards the eavestrough, I simply trimmed those branches to a reasonable height. I then trimmed the spent blooms and called it a day. You can also do a bit of light thinning to encourage new growth.
A more aggressive pruning, perhaps on older shrubs that haven’t been regularly maintained, should be done in late winter or early spring. At this point, you want to cut out older wood and malformed stems, and keep the newer stems to encourage new growth. Cut the older stems down to the ground.
With the Bloomerang lilac, I’ll just trim any especially long pieces to maintain the shape of the shrub. Bloomerangs have a nice rounded habit in the first place, so you don’t have to worry about shaping the bush too much. Mine has been in the garden for a few years and it’s still nice and small and compact.
Removing lilac suckers
Another part of pruning lilacs is removing the suckers. What are suckers? Around my lilac there are a few new lilac trees—single stems a few feet away, shooting up from the soil, making their presence known. These are the suckers. I simply cut them off at the soil line (or slightly below). However stems close to the trunk of the bush itself, you may want to leave, as a healthy lilac has a mix of old and new stems. You could also dig up the suckers and replant them elsewhere. Who doesn’t love new plants?
Suckers that aren’t close to the actual lilac are simply trimmed at the soil line.