Gardening

Keep Your Lilac Young: Remove Its Oldest Branch Each Year

Selectively remove the oldest branch each year
will help keep your lilac young and vigorous.

By Larry Hodgson

Lilac season is one of my favorite times of the year. The heady perfume of their flowers brings back memories of my great-aunt Sadie who grew two of them in the front yard of her old farmhouse. And they’re so long-lived that, if the house is still standing, I’ll bet the lilacs are too.

My father always pruned hers for her after they finished blooming, so in late spring. No, he didn’t deadhead (go over the whole plant selectively removing faded flowers). That seems to be a thing these days, but it takes forever. And really doesn’t give anything to the old-fashioned common or French lilac (Syringa vulgaris), other than removing its seed capsules.

Male evening grosbeak in winter.
If you deadhead your lilacs, what will the evening grosbeaks (Coccothraustes vespertinus) have to eat in the winter? Photo: hstiver, depositphotos

And those are the same seed capsules that would otherwise feed beautiful evening grosbeaks in the winter. So, I really don’t get it.

Plus, deadheading lilacs leaves you open to injury as you struggle up a stepladder to reach those always-just-out-of-reach faded blooms.

To learn more about why deadheading lilacs is largely a waste of time, read Garden Myth: Deadheading Lilacs Improves Bloom.

Daddy’s Way

My dad never wasted time with deadheading. Instead, he did was in fact a sort of maintenance pruning. Each year, he’d cut off one branch (two on a very vigorous specimen). Always the tallest one . . . and the oldest. And I’ve been doing the same thing.

The idea behind this annual rejuvenation pruning is to keep the shrub at a reasonable height while encouraging healthy younger shoots that will become the heaviest bloomers.

Most common lilacs will reach up to 20–23 ft (6–7 m) in height if left unpruned. That’s 2 stories! And that puts their deliciously scented flowers well above your head. I mean, you can barely see them, let alone smell them.

Old lilac branch with hollow base.
Often the older branches, the ones you’ll want to remove, are hollow. This is caused by an insect: the lilac borer. Photo: 27east.com

But removing one of the older, taller, out-of-reach branches that shades out the others gives renewed life to the entire shrub. It will respond to harsh pruning by sending up one or more new and vigorous branches. Do this every year to an overgrown lilac* and within 5 years, it will be within an easy to reach 6 to 10 feet (1.8 to 3 m) tall with a denser, more floriferous habit. And it’ll maintain that height as long as you keep the pruning up!

*If a lilac is really seriously overgrown, you might indeed want to take out 2 branches a year for the first 3 or 4 years. Just to get things started.

Take It All Off!

How far back to you need to prune these big branches? To the ground or as close as you can get to the ground. Say, 6 inches (15 cm), 1 foot (30 cm)? Something in that range. You’ll need a saw. Maybe even a small chainsaw (lilac wood is hard). And while you’re at it, you can remove suckers too. At any season. Most common lilacs produce far too many of them!

Removing old branches also helps solve another problem: dealing with lilac borers (Podosesia syringae). They pierce holes in lilac bark and empty out the inner wood, leading to weakened branches that bloom less and can break off. However, they rarely attack branches less than 1 inch (2.5 cm) in diameter. So, by removing larger, older branches, you’re also removing lilac borers . . . thus killing two birds with one stone!

Illustration showing where to cut back lilac branch.
Cut back the oldest branch to the ground or as close to ground as you can. Ill.: njaes.rutgers.edu

Do note that newly sprouted lilac branches won’t reach blooming size for at least 3 years, and more likely 4. Even 5! So annual maintenance pruning will most affect seriously improve flowering in the medium and long term, not the short one.

But then, don’t they say, “Lilacs are forever?” Oh, was that diamonds? I could have sworn it was lilacs.

When to Do Maintenance Pruning?

Theoretically, the ideal time to cut back an old branch in order to stimulate regrowth would be in early spring, before the plant blooms. But . . . who wants to cut back a lilac in bud just about to flower? So, most gardeners compromise and instead prune right after the lilac blooms. That will still give the replacement branch time to grow and harden off so it will be ready to continue its growth in year two.

Laidback Lilac Rejuvenation in a Nutshell:

  • Once a year;
  • With 3 weeks after flowers fade;
  • Cut the tallest, oldest branch back to the ground;
  • Remove any dead or damaged branches;
  • Go back to your hammock and have a snooze.

Passing On the Pruning Shears

I’ve always pruned my lilacs according to Dad’s method. For nearly 50 years now. But this year, I made a major change.

I had my stepdaughter, Mélissa, come over last weekend and handed her the electric chainsaw. I can longer handle the job, so it will be up to her to take care of her mom’s lilacs. She has clear instructions to come back every year after the lilacs have stopped blooming. And to cut back the tallest branch on each shrub.

Double-flowered very pale pink lilac Krasavitsa Moskvy.
Marie’s favorite lilac ‘Krasavitsa Moskvy’. Photo: vodolejl, depositphotos

And her mom, Marie, does love her lilacs. I planted them for her. She brings in huge bouquets annually and gives others to our less fortunate neighbors. Especially the gorgeous double ‘Krasavitsa Moskvy’, with pink buds opening into ever-so-scented pale pink to white rose-shaped flowers. She adores it!

Garden writer and blogger, author of more than 60 gardening books, the laidback gardener, Larry Hodgson, lives and gardens in Quebec City, Canada. The Laidback Gardener blog offers more than 2,500 articles to passionate home gardeners, always with the goal of demystifying gardening and making it easier for even novice gardeners. If you have a gardening question, enter it in Search: the answer is probably already there!

20 comments on “Keep Your Lilac Young: Remove Its Oldest Branch Each Year

  1. Susan Fagin

    Thank you for the lilac pruning information. I received three lilac starts from my sister just over a year ago. They are growing nicely, but they haven’t actually blossomed yet. How long will that take? They’re only about two feet high, but have lots of leaves and look quite happy.

    • Lilacs are stupendous plants, but slow to bloom. Don’t expect much before 4 or 5 years.

      • Thank you for letting me know I have 4 more years to see the lilac blew.

  2. Excellent advice. The torch has been passed on to the next generation. My husband tackled our huge lilac hedge this year after 22 years. A massive undertaking that we should have gotten to earlier. Ours are Preston Lilacs and since they don’t sucker it will be interesting to see how they respond. We also have three Krasavitska Moskovy’s and they are incredibly fragrant.

  3. Christine Haulgren, Bellingham WA

    I always enjoy reading your posts, and find your gardening advice sensible and helpful. Just have to add this note about the lilac borers: they were responsible for hollowing out a branch on my very old double-white late blooming lilac (came with the house 40 years ago) and one year a pair of chickadees moved into the cavity and raised a family. I loved hearing the babies “peeping” way down safely inside that branch until they fledged. So, nature knows what she’s doing! Chris

  4. Sheila Bannerman

    Thank you for your columns and good information!
    I have a very old lilac tree, not a bush or hedge. Can anything be done to rejuvenate this venerable old member of the family?

  5. Your link to the garden myth about deadheading lilacs doesn’t work.

  6. ‘Alternating canes’. That is how I know it. It works well for several types of plants, including forsythia, abelia, elderberry, mock orange and Heavenly bamboo (Nandina). It is similar to removing old rose canes as they are replaced by newer canes (above the graft union, of course). I do not know what is so difficult to comprehend about this concept, but no one seems to know how to do it. Most people cut off the ‘suckers’ of lilac, to preserve the deteriorating old canes.

    • Interesting! I’d never heard a term for it! Thanks! 👍

      • You are welcome. It is standard procedure for me, so it annoys me that other gardeners do not perform it, even by another name. Nandina can be so pretty if pruned properly, but is normally rather . . . unappealing.

  7. Christine Lemieux

    I have been rejuvenating a Preston lilac. Your Dad’s method would have been a better way to go! You were so fortunate to have had him as a teacher at a young age. I absorbed a love of gardening from my Mom; such a gift. I didn’t know that Evening Grosbeak benefit from lilac blooms. I always learn something from you.

  8. M.A. Unglenieks

    I was gifted an “ever blooming lilac” several years ago. It’s beautiful and the blooms are fragrant but I don not know when to prune it as it has some blooms on it all summer. Thank you for all the wonderful information!

    • Just cut off the dead blossoms. And after several years, start pruning out old, less floriferous branches to leave more room for new, healthy ones.

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