Shrubs are valuable components of a home landscape. Shrubs screen views, provide privacy, and attract wildlife. Many are planted for their flowers, colorful fall foliage, or attractive fruit. To keep them healthy and attractive, home gardeners should prune their shrubs on a regular basis.
While pruning is necessary, many individuals fail to properly prune their shrubs because of a lack of knowledge, time, or courage. As a result of this neglect, plant health and aesthetics decline. A case in point are large, overgrown lilacs. The common purple lilac is a tough, reliable shrub that may eventually reach a height of 15 to 20 feet. To keep lilacs healthy and vigorous, home gardeners should remove a few of the oldest stems (branches) every 2 to 4 years. Neglected, unpruned lilacs often become leggy, unattractive, and don't bloom well.
Proper pruning can renew or rejuvenate old, neglected lilacs and similar deciduous shrubs. One way to renew large, overgrown shrubs is to cut them back over a three-year period. Begin by removing one-third of the large, old stems at ground level in late winter (March or early April). The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of the new shoots. Retain several well-spaced, vigorous shoots and remove all the others. Finally, remove all of the remaining old growth in late winter of the third year. Also, do some additional thinning of the new shoots.
A second way to renew a large, overgrown lilac is to cut the entire plant back to within 4 to 6 inches of the ground in late winter. This type of renewal 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 and remove all others at ground level. Head (cut) back the tallest shoots to just above a bud to encourage branching. Large, overgrown honeysuckles, forsythias, spireas, and dogwoods can be rejuvenated in this manner. Lilacs renewed by this method may not bloom for 3 or 4 years. Pink-flowering spireas usually bloom by mid-summer of the same year.
Once overgrown shrubs have been rejuvenated, pruning should be a regular part of a home gardener's maintenance program. Most deciduous shrubs can be kept healthy and vigorous by removing a few of the oldest stems every 2 to 4 years.
This article originally appeared in the February 27, 1998 issue, p. 15.