Pruning Lilacs

For the absolutely perfectly shaped lilac bush you need to prune them each year. Pruning is a very important part of growing and caring for Lilacs. While some varieties only grow 4 to 8 feet, others can reach up to 30 feet tall. Many will grow in excess of 10 feet. Pruning will not only help with shape and appearance, but also impact health and vigor and the profusion of flowers.

When to Prune a Lilac

There are right and wrong ways to prune a lilac bush. There is also a right and wrong time. Most importantly, prune or trim back your bush immediately after they are done blooming. Make sure to remove the spent bloom with your clippers. This will keep the plant from growing seeds and encourage creation of next year’s buds. Next year’s flower bud develops early even though you do not see it. I have seen inexperienced gardeners trim off the next year’s flowers with one pass of the hedge trimmer. By the way, I do not recommend using hedge trimmers as it gives a too sheared appearance. Lilacs are not hedges.

How to Prune a Lilac

Lilac bushes should be pruned and maintained each year for a well-shaped healthy plant. The plants should be full looking, yet not overly bushy. If the plant is too bushy, the inner leaves do not get sun and air circulation, making it an easy target for plant disease.

Seven Steps for Pruning a Lilac

  1. Prune Old Dead Flowers
    First clip old dead flowers at the base. This is known as deadheading a lilac. Pruning should be done immediately after the flowers have died off.
  2. Prune Near Ground Level
    Cut suckers and shoots at or near ground level or where it comes out of the main trunk.
  3. Save the Strong Stalks
    Leave a few strong and healthy new stalks each year, especially if you are planning to trim back old wood.
  4. Trim the Center Area of the Lilac
    Trim larger stems from the center of the bush to increase ventilation. It will also afford more room for newer shoots on the outside of the plant to develop.
  5. Prune to Create an Appealing Shape
    Trim back any branches that stick out from the main bush and are not appealing to you.
  6. Do Not “Top” a Lilac Bush
    Topping the bush is not recommended. A flat top is not an appealing lilac to most lilac lovers. A slight rounding to the top looks best.
  7. Lilacs Can Be Pruned to be Tall or Wide – Your Choice!
    In trimming and pruning your bushes, remember beauty is in the eyes of the beholder. If you like a tall bush let it grow tall. If you prefer a wide bush, encourage shoots that have spread out from the main bush.

How to Prune Mature Lilacs

Far too often you see a lilac that hasn’t seen pruning since it was planted. Plants that have been let go this long only produce a few sparse blooms 10 feet in the air and old trunks look decidedly unhealthy.

Two ways to Prune a Mature Lilac

  1. Cut back entire lilac plant
  2. Slowly prune over the course of three years

1. Cutting Back the Entire Lilac

One way to renew a large, overgrown lilac is to cut the entire plant back within 6 to 8 inches of the ground in late winter (March or early April). This severe pruning will induce a large number of shoots to develop during the growing season.

In late winter of the following year, select and retain several strong, healthy shoots to form the shrub framework and remove all the others at ground level. Head (cut) back the retained shoots to just above a bud to encourage branching. I proceed in this manner when a plant has reached that point of no return and drastic measure are called for.

2. Pruning a Mature Lilac Over the Course of  Three Years

A second way to prune old lilacs is to cut back the overgrown shrubs over a three-year period. Begin the procedure by removing one-third of the large, old stems at ground level in late winter. The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of the new growth. Retain several well-spaced, vigorous stems and remove all the others. Finally, remove all of the remaining old wood in late winter of the third year. Additional thinning of the new shoots should also be done. Since lilac wood needs to be 3 or more years of age before it blooms, this pruning method should allow you to enjoy flowers every spring. This is my usual mode of rejuvenation pruning lilacs. It provides a smoother transition for the plant and often more importantly a smoother transition for the lilac’s owner…

When properly pruned, an old, overgrown lilac can be transformed into a vigorous attractive shrub within a few years. Once rejuvenated, pruning should be a regular part of the maintenance program for lilacs. The shrub can be kept healthy and vigorous by removing a few of the old branches every 3 to 5 years, and there is no good reason the plant shouldn’t live for another century.