Trimming Lilac Bushes

Written by April Reinhardt (last updated September 12, 2022)

Growing as shrubs, small trees, or large bushes, lilac bushes are deciduous bushes bearing large flowers in early spring. Lilac bushes can grow from four to eight feet in height, while there are varieties of lilac tress that grow to heights of thirty feet. Lilac bushes always flower if left unpruned. If pruned or trimmed incorrectly, lilac bushes will not flower at all, since they spend all of their energy trying to regenerate lost branches, instead of growing flowers.

When lilacs flower, they flower on old wood. Meaning, they do not flower on new stems. If you trim a lilac bush in the fall, you are trimming away the flower buds for next spring, and the bush will not flower for one to five seasons. Therefore, it is best not to trim a lilac bush if you want it to flower profusely every year. But, there are times when you need to trim a lilac bush because it has grown out of control. Follow these guidelines to trim a lilac bush, while still anticipating its lovely flowers in the spring:

  • Immediately after flowering is complete is the time to trim a lilac bush. Once the flowers are mature, clip them with pruning shears and place them in a vase to enjoy. Do not let the flowers go to seed. Clip the flowers about two inches below the last flower petals, forcing two buds to form where one flower had been.
  • Reach into the middle of the bush and trim away any dead branches, or those that have no buds. Thinning the bush of dead branches ion the middle also helps to improve light and air circulation to the entire bush.
  • Shape the bush by removing scraggly branches, and trim in a rounded shape the entire bush by clipping the ends of stray branches. Never cut the top horizontally. Always aim for a rounded lilac bush for a more natural appearance.
  • Lilac bushes grow tiny branches from the root's crown at the base of the bush, called suckers. Cut down suckers, leaving just a few. The suckers will grow into the base of the bush, providing new shoots that will bloom in about three years.

You may also choose to transplant the suckers after a few years, creating more lilac bushes in other parts of your landscape. Lilac bushes grow better in slightly alkaline soil, so you may want to have your soil tested for its pH level to ensure a proper growing environment. It is always best to prune lilac bushes from the inside out to improve air circulation, since they are prone to powdery mildew disease.

Author Bio

April Reinhardt

An admin­istrator for a mutual fund man­age­ment firm, April deals with the writ­ten word daily. She loves to write and plans to author a memoir in the near future. April attend­ed More­head State Uni­ver­sity to pursue a BA degree in Ele­men­tary Edu­ca­tion. ...


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