One of the most important cultural practices for maintaining woody ornamental plants is pruning. Pruning is an art in making the pruning cuts properly, and a science in knowing the proper methods and time to prune for maximum benefits. Pruning can help train or direct plant growth to a particular space, like a formerly pruned hedge. Pruning can also control the shape and size of a plant like a hedge pruned to a particular height. Unfortunately, many people do not have a full understanding of pruning.
Proper pruning requires a basic understanding of how plants respond to pruning. The terminal bud on the end of the branch secretes a hormone that directs control of the growth of the lateral buds (buds on the side of the branch). The terminal bud suppresses the growth of the lateral buds when intact. When the terminal is pruned out, the lateral buds and shoots begin to grow. The most vigorous new growth always occurs within 6 to 8 inches of the pruning cut.
Often, a shrub is pruned by shearing the new growth to control its size and shape. Continually shearing shrubs causes a lot of dense, thick, new growth to be produced near the outer portions of the canopy. Less light reaches the interior portions of the plant, leading to sparse foliage with a leggy or hollow appearance. Thinning removes an entire shoot or limb to its point of origin from the main branch or lateral branch. Some of the shoots are not pruned. It allows the plant to have a more natural growth form. Thinning cuts shorten the branches, improve light penetration and directs the growth of shoots or limbs. It encourages new growth within interior portions of a shrub, reduces size and gives a fuller, more attractive plant. Proper pruning should involve a combination of both of these techniques to keep a plant at a chosen size, shape and density.
Often, a shrub is overgrown, and it needs renewal or rejuvenation pruning. This involves severe pruning to bring the plants back under control. Renewal pruning involves cutting the plant back several feet closer to the ground. Early spring, from late February into March, is the best time of the year for renewal pruning. Do not do renewal pruning in fall or winter. You will have ugly, bare wood shrubs until the spring growth occurs. Renewal pruning is often only a temporary solution to overgrown shrubs. It may need continual severe pruning. Consider removing such a shrub and planting a species that grows more slowly and remains smaller. Most broad-leaf ornamentals, like ligustrums, hollies, crape myrtles and cleyera, respond well. Boxwoods recover slowly and can die when subjected to severe pruning. Narrow-leaf evergreens, like junipers, Leyland cypress and arbovitaes, do not respond well to this type of pruning. They often die as a result. Consider removing overgrown narrow-leaf evergreens and replacing them with smaller ones.
The best shape for a pruned shrub is a pyramidal shape with the narrowest part of the hedge at the top tapering to a wider base. A pyramidal shape allows adequate light to reach the lower portion of the canopy. If the widest part of the hedge is at the top with it being narrower underneath, the undergrowth will be shaded out, and the growth will be thin and aesthetically unpleasant.
The best time to prune varies with plant species and should be done at times that complement the growth characteristics, flowering and other objectives you desire. Prune woody ornamentals according to their date of flowering. Spring-flowering shrubs, like forsythias, flowering quince and azaleas, should be pruned after flowering. Pruning before flowering will remove the flower buds that have formed in the fall. Summer-flowering plants generally are pruned after flower and often during the dormant winter season. Vitex (chaste tree), tea olive and roses can be pruned in the dormant season since they flower on the new growth. Plants flowering before May should be pruned after they bloom, while those that flower after May are summer-flowering and can be pruned just prior to spring growth. One exception to this rule is the oakleaf hydrangea, a summer-flowering shrub that forms flower buds the previous season.
Pruning plays an important role in the development and maintenance of woody plants. Developing clear pruning objectives is important, and combining them with a basic understanding of pruning and the response of plants, you can derive maximum benefit from the effort.
Timothy Daly is an agricultural and natural resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or firstname.lastname@example.org.