Key Points
Pruning lilacs in fall can ruin next year’s blooms since flower buds form from late summer to early fall.The best time to prune lilacs is right after spring flowering—within about six weeks—to shape plants without losing blossoms.For healthier growth, remove one-third of old stems each year, keep tools sharp, and avoid shearing with hedge clippers.
Lilacs add beauty, scope, and vertical height to your landscaping. A longtime favorite of gardeners, lilacs boast beauty and longevity, with some varieties living more than a century with proper care. To prolong their lifespan, pruning is among the most important maintenance requirements for lilacs.
Lilacs are fairly self-sustaining once they’re established, but pruning is often used to control the shape and size of these substantial shrubs—without regular attention, lilacs can grow tall and narrow.
However, pruning at the wrong time can cause more harm than good. While you may be tempted to give your lilac shrub a haircut before winter, we consulted gardening experts to learn whether now is a good time to prune or not. Here’s what they said.
Should You Cut Back Lilacs Before Winter?
While pruning your lilac before winter won’t necessarily kill the shrub, fall and winter are definitely not the preferred seasons for this task. “Lilacs set their buds for next year’s bloom from late summer to early fall,” explains horticulturist Christine Froehlich. “Cutting them back in the fall will sacrifice next year’s flowers.”
Simply put, if you want your lilac to bloom next spring, avoid pruning in the fall and winter. Exceptions would be rejuvenation pruning to remove dead wood or to reduce the size and leggy habit of the shrub, says Froehlich. “This can be done in late fall or early spring, but you would still sacrifice some of the flowers,” she cautions.
The Best Time to Prune Lilacs
Instead of fall, many gardeners recommend pruning lilacs in late spring or early summer. “Always cut them back after they are done blooming in the spring,” suggests horticulture educator Irish-Hanson. Froehlich adds that lilacs should ideally be pruned within six weeks after they flower, typically from June to early July.
Lilac Pruning Tips
Try these helpful pruning tips for optimal success with your lilacs.
Use the Rule of Thirds
It’s possible to perform some long-term structural pruning while still enjoying flowers in the spring. “Most common lilacs bloom on wood that is three years old,” says Irish-Hanson. “If you want to have blooms while removing some of the largest stems, follow the rule of thirds.”
She explains that in the first year, gardeners remove one-third of the largest stems immediately after spring flowering is complete. “In the second year, remove the second third (or half of the remaining largest stems), and in the third year, remove the remainder of the large stems.” She notes that this process opens up the canopy and encourages the growth of newer stems while still providing flowers each year.
Research the rule of thirds before attempting it. “Some people think the rule of thirds means removing the growth from the top (or bottom) third of the plant,” says Irish-Hanson. “This does not work well and can lead to poor form and fewer flowers at the top of the plants.”
Maintain Your Tools
Hand pruners or loppers are typically the tools gardeners use to cut back lilac shrubs, but it’s important to keep them maintained. “Dull pruners, loppers, or saws are problematic,” says Irish-Hanson. “Dull blades typically leave ragged wounds that do not heal well.”
Learn Technique
It’s also wise to learn a bit about proper branch lopping techniques. “Cuts should be made at the apex of two connecting branches rather than being lopped off indiscriminately,” says Froehlich. “The most common mistake (one of my pet peeves) I see is shearing them with hedge clippers, especially the dwarf Korean varieties such as ‘Miss Kim’ and ‘Palibin.’ It not only looks bad but creates a shrub with little or no interior growth.”
Research Your Variety
The exact pruning methods and scheduling may depend on your particular lilac variety. “For other types of lilacs, like Korean and Meyer lilacs, rejuvenation pruning can be done during later winter,” says Irish-Hanson. “Rejuvenation pruning removes all the stems to the ground. The plants may not bloom for one to two years.”
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