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Pruning lilacs to promote blooming and reduce disease

Traditional lilacs found throughout New England are light purple.
Traditional lilacs found throughout New England are light purple.
Ann Althouse / Flickr

Country roads adorned with clumps of lilacs (Syringa vulgaris L) brings back memories of quiet nights when the perfume of lilacs lay heavy in the air. These attractive shrubs survive for hundreds of years once established. In fact, across New England it is a tradition to take a piece of the old lilac tree when moving to a new location and is not unusual for several generations to grow a piece of the same lilac tree.

Why Prune Lilacs?

Many allow lilacs to grow wild on their own without pruning, but there are several reasons to prune your lilacs regularly.

  • Control Height - This keeps the blooms where you can reach them and enjoy them.
  • Reduce Disease - Improved air circulation and sunlight reduces chances of diseases.
  • Stimulate New Growth - Pruning forces new shoots to form and increase blooming.

When Should You Prune Lilacs?

Keeping lilacs healthy and producing abundant blooms requires regular pruning, but beware of when you prune. Because lilac trees produce the bud for next year's flowers by mid summer, pruning them in the fall or spring will remove the buds and inhibit blooming. Lilacs are best pruned immediately after blooming to avoid cutting off the buds for next year's blooms.

Tools Required

Margorie Poronto from the University of Maine Cooperative Extension recommends a pruning saw for removing old wood larger than 1 1/2 inches in diameter, a pair of loopers for branches between 1 and 1 1/2 inches and a set of hand pruners for smaller branches. Choose the cutters or pruners that work best for the size of the branches.

Prune Out Old Wood

The first step to pruning your lilac shrub is to cut out one third of the old wood. This allows air to circulate through the center of the shrub and encourages young shoots to take over. Cut them to the ground level with the pruning saw.

Remove Damaged or Dead Wood

Take the time to remove any damaged or dead wood from your lilac shrub. Both should be cut back to healthy wood or cut back to the ground level.

Finishing the Job

Prune away any branches that cross the center of the shrub to open up the area. Trim branches outside the overall shape of the bush by cutting them back to the desired length. This is the time to remove suckers from the outside of the clump of lilacs.

Extremely overgrown lilac trees can be cut back to the ground level to rejuvenate the shrub, but it will take several years before the tree blooms. By removing one third of the oldest wood for three years, you will have revived the lilac shrub while still enjoying the blooms. Prune as needed after the first three years.