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When Is the Best Time to Prune Lilacs?

woman pruning lilac tree in backyard

The signature floral smell of lilac is a sure sign that spring has sprung! If you have a fragrant lilac bush in your yard, you may wonder if and when you need to trim it. The best time to grab your clippers and get to work is in early summer after the flowers have bloomed and faded. Here’s what you should know about caring for lilac bushes and trees.

Why You Should Prune Your Lilacs in Early Summer

Lilacs grow the next season’s flower buds in early summer, immediately after their flowers fade. If you put off pruning until later in the season, you risk removing the developing buds.

This is equally true for lilacs such as Bloomerang Purple that bloom twice a year. By pruning the bush after its initial bloom, you encourage new growth and more flowers in its second bloom in early fall. Pruning gives the new shoots more time and energy to develop so that the bush can remain healthy and hardy over winter.

Can I Prune Lilacs in the Late Summer or Fall?

Generally, mature lilac bushes should be pruned right after the flowers have faded in late spring or early summer. Lilacs grow the next season’s flower buds in early summer, immediately after the current year’s flowers have faded. Therefore, if you put off pruning until later in the summer or fall, you risk removing the developing buds. For instance, avoid pruning lilacs after July to ensure you have flowers next spring.

Why Should You Cut Back a Lilac Tree Annually?

If left to grow and spread on their own, lilac bushes will eventually only flower at the tips of their uppermost branches. Once a lilac bush is over two years old, it requires annual pruning. Removing dead, diseased, broken and weak stems helps rejuvenate the shrub and make it more visually appealing. It also encourages a bushier growth habit.

Annual pruning also keeps your lilac bush from becoming tall, leggy and unmanageable. After all, some lilac varieties can grow anywhere from 12 to 24 inches yearly.

Types Of Lilac Bush Pruning

There are two techniques for pruning lilac bushes: maintenance pruning and rejuvenation pruning:

  • Maintenance pruning

Maintenance pruning ensures your lilac bush remains constantly vital, with new stems developing as old stems bloom.

  • Rejuvenation pruning

Rejuvenation pruning gives an old, overgrown, neglected lilac bush new life. It involves cutting the shrub back to about 6 to 8 inches above the ground. To avoid interrupting the bush’s bloom cycles, rejuvenation pruning can be done over two years. Hard-prune half of the shrub’s stems during the first year and the remainder during the second.

How Do You Prune Lilacs?

Using a sharp pair of shears, follow these guidelines when you prune your lilacs:

  • Get rid of dead, broken or diseased stems first, as well as any weaker branches. In addition, cut branches to prevent rubbing or crossing.
  • Remove old stems that are thicker than two inches. This prevents your lilac from growing too tall and encourages the growth of young shoots. The stems should be completely removed.
  • Manage sucker growth. Suckers are new shoots that grow around the base of the plant. A couple of strong suckers can be retained to replace main branches, but all weaker suckers should be cut at the soil line so that they don’t steal away nutrients.

Finally, there are a few rules of thumb to follow when pruning lilacs:

  • Trim mature lilac bushes so that they remain within 6 to 8 feet.
  • Aim to have 10 to 12 main stems, each of them 1 to 2 inches thick.
  • Never prune more than one-third of the bush.
  • Create a balance of older stems and new flowering shoots.

If you don’t feel confident pruning your lilac bush, the arborists at ArborCare® can help. We offer professional pruning, trimming, shaping and restoration services.

Qualified Arborist in Calgary, Edmonton, Kelowna and Winnipeg

If you need help determining when and how to prune the lilacs in your yard, look no further than ArborCare. Our expert arborists can provide expert plant management tips and advice on how to prune your lilac tree to keep it looking its best for years to come. Contact us today to find out more about our tree care services or to schedule an appointment in or near Calgary, Edmonton, Kelowna or Winnipeg.

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