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Issue: March 6, 2010

Prune lilacs after they flower

When should I prune my lilacs? I moved into my house last summer and have lilacs that are about 3 feet high.

Suzanna D. Belen

A. Lilacs should be pruned in the spring after they flower. The flower buds form in the late summer, so pruning during the dormant season will result in the loss of the spring blossoms. When they flower you will notice that the top pair of buds (and often the second pair) will be flower buds that produce only flowers and no leaves. After the flowers fade, you can cut the stem back to where the vegetative (leaf-bearing) stems form.

In the case of your lilacs, they are small and will need little pruning other than that described above. Larger lilac shrubs may grow to be so large that more extensive pruning is needed. This can be done after flowering, or during the dormant season. If you are pruning large stems, dormant season pruning will be least debilitating for the shrubs. However, lilacs are vigorous and tolerate pruning that many other plants will not tolerate. Dormant season pruning will remove the flower, however, so the recommended method for pruning larger shrubs is to remove only a few of the oldest (biggest) stems from the center of the shrub. The flowers on these stems will be lost, but if you leave other stems, there will still be flowers produced. Removal of a few of the oldest stems each year, leaving other, younger stems, is called rejuvenation pruning. This allows you to manage the size of the plant and still have flowers each year. This encourages production of new stems from the base of the plant. These new stems will flower in one to two years and produce more, and better, flowers than the old stems. Rejuvenation improves flower quality in lilacs and some other early spring flowering shrubs.

For more gardening information, visit the NMSU Extension publications World Wide Web site at http://www.cahe.nmsu.edu/pubs/_h.

Send your gardening questions to:

Yard and Garden, ATTN: Dr. Curtis Smith
NMSU Cooperative Extension Service
9301 Indian School Road, NE, Suite 112
Albuquerque, NM 87112

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.