By Richard Jauron
Horticulturist
Iowa State University Extension
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 can also provide privacy, block views and attract wildlife. To perform well in the landscape, most shrubs need to be pruned on a regular basis. 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 two or three 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 large, overgrown and unattractive. Flowering shrubs that are not pruned on a regular basis may not bloom well.
Proper pruning can renew or rejuvenate overgrown, deciduous shrubs. One option is to prune them back over a three-year period. Begin by removing one-third of the largest, oldest 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, new 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 should also be done.
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. Overgrown lilacs, dogwoods, privets, honeysuckles and forsythias may be pruned in this manner. (Most lilacs rejuvenated by this method will not bloom for two to three years.) This method is also an excellent way to renew scraggly potentillas and summer-flowering spireas. For best performance, potentillas should be cut back to within 3 to 4 inches of the ground about every three years.
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.
While unattractive, old shrubs may not appear to be salvageable, it is possible to renew or rejuvenate many deciduous shrubs with proper pruning. Once rejuvenated, regular pruning will keep the shrubs full, healthy and attractive.