How To Prune Overgrown Lilacs

Posted on: 29 April 2015

If you are fortunate enough to have lilacs (Syringa vulgaris) on your property, you already know that these spring-blooming flowers release a heady, sweet scent that perfumes the night air. What you may not know is that without regular trimming or pruning your lilac bushes can become overgrown and gradually produce fewer blooms. Knowing when and how to prune them is important to keeping them healthy and producing abundant blooms.

Pruning Overgrown Lilac Bushes

Ideally, your lilac bush should grow to a height of 8 to 12 feet with a rounded or oval canopy that spreads 6 to 12 feet, creating a compact shrub that produces an abundance of flowerheads in the spring. Older bushes, particularly if they have not been trimmed, may grow taller and lose the foliage near the bottom, giving your lilacs a ragged and uneven appearance. You have two choices for reviving the bush.

  1. Cut the entire lilac bush to the ground, leaving 6- to 8-inch stumps. New shoots will soon emerge from the base of the bush and new growth will replace the old bush. This method means your lilacs may not bloom for several years, but it will produce healthy young trunks to support blooming. Lilacs typically resume blooming in 3 to 5 years, depending on their growth rate.
  2. Selectively remove old wood to allow air and sunshine to reach the center of the bush and encourage healthy, new growth. This method allows you to continue to enjoy spring blooms, but typically requires three years to revitalize the bush.

How to Selectively Remove Old Wood

As your lilac matures, some of the branches begin to die or produce fewer blooms. Removing the overgrown or misshapen branches allows new growth to flourish. 

  1. Cut one-third of the old growth to the ground level in late winter or early spring before new growth appear. You can use either a handsaw or power saw to cut your lilacs, but use caution not to nick or damage nearby branches or trunks.
  2. Select the oldest trunks at this time.
  3. Look for branches or trunks that are dead or dying and remove them.
  4. Examine the bush for any branches that appear twisted or cross the center of the bush. Removing these opens the bush up and encourages airflow, which in turn reduces the chances of disease and encourages healthy growth.
  5. Repeat the procedure in late winter or spring for the following two years. At the end of the third year, your lilac bush will consist of all new growth.

Pruning Your Lilacs to Maintain Their Shape

Once you have revived your lilac bushes, they will require regular pruning or trimming to maintain their shape and prevent them from overgrowing. While light pruning to nip off the ends of wayward branches can be done at any time, there are some potential problems. Lilacs form the buds for the following year's blooms shortly after they cease blooming. Pruning them in the summer or fall may remove the buds and prevent the bush from blooming the following year. If you must trim your lilacs in the summer, do so immediately after blooming, before the buds begin to form. Some prefer to remove the faded blooms with a pair of pruning shears to improve the appearance of the bush, but it is not necessary.

With regular pruning to keep your lilac bush healthy, it will continue to bloom for years. Lilac bushes planted on New England homesteads have been known to survive for hundreds of years. In fact, the lilacs at the Governor Wentworth estate in Portsmouth, NH are thought to have been planted in approximately 1750. They are believed to be the oldest living lilacs in North America. If you're interested in more information about landscaping, contact tree trimming professionals.


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