One of the most important ways to maintain woody ornamental plants is to prune.
Pruning, as it turns out, is both an art and a science. The science part comes in knowing the proper methods and time to prune for maximum benefit, and the art is making the pruning cuts properly.
Pruning can help train or direct plant growth to a particular space, such as a pruned hedge. Pruning can also control the shape and size of a plant, such as 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, or the buds on the side of the branch. If the terminal bud is left intact, it suppresses the growth of the lateral buds. 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, on the other hand, 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. 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.
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, the undergrowth will be shaded out and the growth will be thin and aesthetically unpleasant.
The best time to prune varies with plant species. You should choose a time 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, because 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.
Often a shrub is overgrown, and it needs renewal or rejuvenation pruning. These severe techniques help bring the plant back under control. Renewal pruning involves cutting the plant back several feet, closer to the ground. Early spring - 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 be left with ugly, bare wood shrubs until the spring growth occurs.
Timothy Daly is an agricultural and natural resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or timothy.daly@gwinnettcounty.