Pruning lilacs is one of the most important steps in lilac care. Learning how to prune a lilac bush is the best way to encourage generous blooms, year after year.
If you haven’t learned how to prune lilac bushes yet, now is the time to learn! This post will teach you when and how to do it without compromising next Spring’s blooms.
Why Pruning Lilacs Should Be a Yearly Gardening Task
If you’ve ever seen a lilac bush in person, you know they can grow several feet tall (sometimes up to 30 feet, depending on the variety you plant) and rather wide.
These bushes can also produce numerous shoots that sometimes intermingle, which can reduce airflow and sun exposure within the bush- something lilacs need in order to grow well.
These individual shoots can also make the bush less attractive, which is why some people trim them down all the way to the ground before they get out of control.
The biggest problem with forgoing yearly pruning and letting your lilac bush grow wildly is that most of the blooms will grow far above eye-level.
Lilac bushes are beloved for their large clusters of fragrant florets and for their fragrance, so growing them several feet above your head would be a shame! If you have to look up at a 20-foot lilac bush to even see your blooms, then it’s time to prune it down – the right way!
Remember: once you let your lilac bush grow much taller than you, it’s going to be difficult to tame it. It will be far more work-intensive to prune a 15 to 30 foot bush than it would be to prune one that sits at 6 or 8 feet tall.
LILACS – WHEN TO PRUNE
Timing is one of the most important factors when pruning lilac bushes. Once your bush reaches 6 feet tall, yearly pruning should become one of your must-do gardening tasks. Your lilac bush will reach height a few years after planting.
Thankfully, when it comes to lilacs when to prune is not a difficult thing to master. You should always prune lilacs as soon as your blooms have finished blooming for the year.
The best way to tell is by quickly observing the color and texture of the blooms: have the blooms lost their color? Are they turning brown? Do they feel crispy when you touch them? If the answer is yes, then they’re done blooming. They will definitely NOT look as vibrant as these purple beauties do, below.
Since there are literally hundreds of lilac varieties and hybrids, it’s difficult to generalize blooming times.
For instance, some hybrids have been created to thrive in zones that have warmer Winters, such as the “Lavender Lady” variety, which can be grown successfully in zone 9 (Yes, that’s you, So-Cal!).
Why is lilac variety important? The variety is important because some are categorized as early bloomers (early May, or even earlier in warmer zones) while others are categorized as late bloomers (late May to early June). This is why you’ll need to have a watchful eye on your shrub when it comes time to pruning lilacs in your yard.
As soon as you see dead lilac blooms, it’s time to take out your pruners. Make sure you have sharp pruning shears and strong gardening gloves that can protect your hands and forearms. (I like these shears because they’re inexpensive, get the job done, and have thousands of positive reviews on Amazon.)
What To Avoid When Pruning Lilacs
The biggest mistake you can make with pruning a lilac bush is pruning off new wood because that’s where your plant will grow next year’s blooms. If you cut off branches that aren’t spent, your lilac bush won’t produce any flower clusters for you next year. TIP: It’s better to be conservative than overzealous when pruning lilacs.
Also, don’t pull out your hedge trimmer. Hedge trimmers are not ideal for pruning lilac bushes for two main reasons: 1) you might unknowingly cut off next year’s forming blooms while you’re shaping and 2) lilac bushes should hold a round shape rather than a flat-top shape.
PRUNING LILACS AFTER BLOOM
As soon as you see dead blooms on your lilac bush, you’ll know it’s time to do your annual pruning. The way you prune your lilac bush will ultimately depend on how you like your lilac bush shaped.
Some people like a wide lilac bush while others prefer to keep their’s shorter and smaller in circumference.
The rule of thumb, however, is to cut off spent blooms and their individual flower stems, aka “old wood”. Cutting off the spent blooms once you see them will prevent the lilac bush from producing seeds, something you want to avoid because that will take the plant’s energy away from producing the buds that are necessary for forming next year’s blooms.
IMPORTANT: Lilac bushes start to produce “buds” on the end of new wood stems, which is why it’s very important not to over-prune. If you unknowingly trim off the tips of these branches, your lilac bush will not produce any flower clusters for you next Spring.
If your lilac bush has produced smaller shoots that are coming from the ground or o out of the main trunk, go ahead and cut these down to keep a tight, neater shape.
You can also trim off any branches that are sticking out from the middle of the bush, in order to achieve a tamer look. Cutting off larger stems from the middle of the lilac bush will promote better air circulation, too, and let more sun in.
Reinvigorating Lilac Bushes That Are Old or Overgrown
Many people have problems with overgrown lilac bushes that have grown several feet above eye level and have stopped producing flowers.
When this happens, you’ll want to slowly remove 1/3 of the bush’s oldest branches every year because this will encourage the bush to grow new shoots. Remember: new shoots are necessary for producing flower clusters.
This 1/3 method is ideal because it won’t force you to cut down your entire lilac bush to the ground, something that would leave you with zero chances of blooms for several consecutive years.
Gradually getting rid of older wood each year to promote new growth will still leave you with a lilac bush that produces foliage and (hopefully) a few blooms each Spring.
After you cut off the old stems, new shoots will start to grow out from the bush and in three years or so, these new shoots will start to produce large, healthy flower clusters.
Within a few years, you’ll have an entirely fresh lilac bush that should continue to bloom for you for years and even decades to come as long as you prune annually in the appropriate manner and understand everything else that’s required to successfully grow lilac bushes.
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