Lilacs in bloom

How do I prune my lilacs?

I have a friend with a beautiful garden, designed and installed by professional landscapers. She loved it, but her one complaint was that her lilacs had bloomed the first year and then never really put on much of a show after that. When I visited her lovely garden my one question, that revealed the problem, was “When did you prune your lilacs?” It turns out she hadn’t pruned her lilacs, but the guys taking care of her garden (a grass cutting service that purported to also be a gardening service) always pruned them in late summer. This was the problem.

Lilacs set their blooms for the following season shortly after the current year’s bloom is finished. In my part of the world, lilacs usually bloom in mid-May, the flowers die off in June, and then the shoots for next year’s blooms develop in July. If you prune your lilacs after those shoots have started to form you won’t get any blossoms the following year–you’ve cut them off.

Last year, after having this conversation with me, my friend told her lawn service not to touch her lilacs. Recently I asked her if they’d bloomed “they’re beautiful! You should see them!” she said. Yup, nothing wrong with the plants, just the person wielding the secateurs.

 

Pruning is required:

To keep the lilacs blooming my friend will need to cut off this year’s old blooms now. If she doesn’t, the plant will put all of its energy into turning those blooms into seeds, and she won’t get a very good flower show again next year. Her question to me this year: “Where do I cut them?”

Spent lilac bloom being pruned

The answer is: right below the bloom, above the first set of leaves or new growth.

If you want to prune out more of the plant (for shape, or to keep its size in check) you would trim it like any other woody shrub (a good clean cut, right above a growth node). But if all you’re trying to do is ensure a spectacular crop of blooms next year, take 10 minutes this week and cut out all of this year’s finished blooms. If you have a large lilac you may need a ladder–with mine I can get away with just bending the taller branches toward me enough so that I can just reach.

Make sure your secateurs are sharp–it will make pruning a lot easier on you and on your lilac! Learn how to sharpen them here.

 

How to prune lilacs

 

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7 Comments

  1. Garth Wunsch on June 15, 2016 at 8:53 pm

    Didn’t realize I had to prune them so quickly. Thanks

  2. Lynn on June 8, 2018 at 6:23 pm

    My Lilacs have not blumed in two years any suggestions?

    • Jennifer on June 8, 2018 at 6:58 pm

      Thanks for the question Lynn. The most common cause of lilacs not blooming is that the blooms have been cut off the previous year (see first and second paragraph above). If that’s not the case it could be that they’re in too much shade (bigger trees have grown up around them over time and cut off their supply of light).

  3. Christis Jackson on September 12, 2018 at 5:58 pm

    It appears that I have many seeds on each stem. What do I do this late- Sapt?

    • Jennifer on September 12, 2018 at 6:43 pm

      Hi Curtis. I would leave your lilacs alone at this point. If you do any pruning now you’ll cut next year’s blooms off. The benefit of pruning off the old flowers right after they’ve bloomed is to avoid the plant diverting energy into creating seeds–it’s already done that, so there’s no benefit to pruning now. Just make a note in your calendar to prune off the spent blooms next June.

  4. Becky on August 9, 2019 at 7:59 pm

    Hi. I have a very large lilac bush that was doing fine until I hired a landscaper. He started spraying chemicals on my yard and coincidentally? my lilac and several other shrubs started dying. I tried to ask my landscaper about it today and he got so angry and started screaming at me that it wasnt his fault, I had to ask him to leave my property. I had recently had an Arborist out to look at my Hickory trees. He said they had a fungus because of all the rain we had. He said they would be fine after a dry spell. He is the one that suggested that perhaps the chemicals being applied to my lawn were what affected my shrubs. I just want to know how to save them if at all possible. Thank you

    • Jennifer on August 10, 2019 at 5:56 pm

      Hi Becky. Sorry to hear you had such an unpleasant situation with your landscaper! It’s hard to know how badly affected your lilac and other shrubs were–my suggestion is to a)not let anyone spray more chemicals on your yard (removing weeds by hand, or using horticultural vinegar are the only methods we’re allowed to use where I live and that’s a good thing, in my books) and b) put some good compost down around your shrubs to feed them (no need to dig it in, just put it on the top of the soil), and then just watch and see how they do. In the spring, see what’s really dead, and prune those branches off to just above a good, healthy bud, and see how they do. You might not get much in the way of blooms next year. Lilacs are generally pretty tough, so hopefully it will pull through.

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