Shrubs are valuable assets to a home landscape. Shrubs are often planted for their ornamental characteristics, such as flowers, colorful fall foliage, or attractive fruit. They also can provide privacy, block views, and attract wildlife. For shrubs to perform well in the landscape, home gardeners must prune them properly. Proper pruning helps to maintain plant health, control or shape plant growth, and stimulate flower production.
Many deciduous shrubs (those that lose their leaves in the fall) can be kept healthy and vigorous by removing a few of the largest, oldest stems every 2 or 3 years. Unfortunately, many individuals fail to prune their shrubs because of a lack of time, knowledge, or courage. As a result of this neglect, shrubs often become leggy and unattractive. Flowering shrubs that are not pruned properly may not bloom well.
Proper pruning can renew or rejuvenate overgrown, deciduous shrubs. One method is to prune them back over a 3-year period. Begin by removing one-third of the large, old stems at ground level in late winter/early spring (March or early April). The following year (again in March or early April), prune out one-half of the remaining old stems. Also, thin out some of the new growth. Retain several well-spaced, vigorous shoots and remove all of the others. Finally, remove all of the remaining old wood in late winter/early spring of the third year. Additional thinning of new shoots also should be done. This method of rejuvenation pruning works well for any multi-stemmed or cane-type shrub such as lilac, forsythia, beautybush, mockorange, viburnum, and dogwood.
A second way to prune overgrown, deciduous shrubs is to cut them back to within 4 to 6 inches of the ground in 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 and remove all others at ground level. Head (cut) back the retained shoots to encourage branching. Large, overgrown lilacs, honeysuckles, dogwoods, spireas, barberry, flowering quince, and forsythias may be pruned in this manner. Some shrubs, such as lilacs, pruned by this method will not bloom for 3 to 5 years.
Pruning Overgrown Hedges
Deciduous, formal hedges (those pruned to a definite size and shape), such as privets, that become open and leggy also can be rejuvenated by pruning them back to within 4 to 6 inches of the ground in late winter/early spring. To obtain a full, thick hedge, prune (shear) the shoots often as they grow back in spring and summer. Also, make sure the base of the hedge is slightly wider than the top to encourage growth close to the ground.
Other species, such as boxwood and yew, are commonly grown as formal hedges but cannot be renovated in this way. Do not prune these shrubs back into dead portions of the branches as this will create large open gaps in the hedge and these species do not readily fill in those gaps with new growth. If these species of hedge become to large or unattractive, they will need to be removed and new shrubs planted.
Pruning Overgrown Evergreen Shrubs
Large, overgrown evergreen shrubs, such as junipers, are a more difficult problem. Junipers possess bare or dead zones in their centers. They cannot be pruned back severely because they are incapable of initiating new growth from bare branches. Large, overgrown junipers that have become too large or unattractive will need to be removed and new shrubs planted.
Although many overgrown, deciduous shrubs can be renewed or rejuvenated, it's much easier to prune them on a regular basis. Regular pruning will keep the shrubs full, healthy, and attractive.
Updated from articles that originally appeared in the February 10, 1993 issue (p. 8) and March 7, 2003 (pp. 20-21) issues of Horticulture and Home Pest News.