Care of Woody Plants Kentucky Master Gardener Manual Chapter 12
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University of Kentucky College of Agriculture, HO-101 Food and Environment Cooperative Extension Service Care of Woody Plants Kentucky Master Gardener Manual Chapter 12 Adapted from The Virginia Master Gardener Handbook. Edited by Ray McNeilan, extension agent emeritus, Multnomah County, Oregon State University. Adapted for the Kentucky Master Gardener Manual by Rick Durham, consumer horticulture extension specialist and master gardener state coordinator. o prune or not to prune? This is a question that gardeners In this chapter: often faces gardeners. Most feel they ought to prune but are not sure why or how. Pruning is an accepted practice in Reasons for Pruning .........................................157 Torchards and frequently is done in rose gardens, but it is used hap- Pruning Terminology .......................................158 hazardly elsewhere. Ornamentals are most often pruned only when a shrub or tree begins to encroach on its neighbors, a walkway, or a Pruning Tools ......................................................159 building. Basic Pruning Techniques ...............................161 Pruning often is thought of as a way to make a barren tree fruit- Espaliering ...........................................................163 ful. If carried out correctly, it eventually will do so. However, years of neglect cannot be corrected in one season. Gardeners who don’t Shade Trees ..........................................................164 know how to prune but do so because they think they should often Fruit and Nut Trees ............................................164 end up with no flowers at all because they either prune excessively or prune at the wrong time of the year. Keep in mind that pruning Shrubs ....................................................................171 will not compensate for lack of fertilization, poor weed control, or Hedges ..................................................................172 drought conditions. Rose Bushes .........................................................173 What, then, is pruning? Why, when, and how should it be done? Pruning can be described as the removal of part of a woody plant Vines and Groundcovers .................................175 for a specific purpose. This chapter explains the reasons for pruning, For More Information .......................................175 the proper techniques and tools to use, and how to prune various types of plants. Reasons for Pruning Reasons for pruning can be grouped into four general categories: • Training a plant • Maintaining plant health • Improving the quality of flowers, fruit, foliage, and stems • Restricting growth Training a Plant Prune trees and shrubs after transplanting only to remove dead, broken, crossed, or pest-infested branches. Contrary to common belief, it is not necessary to prune away one-third of a tree’s top growth to compensate for root loss as long as you use properly pruned, nursery- grown plants. According to research, excessive pruning at transplanting reduces plant size and does not aid in survival. However, pruning should begin during a tree’s first growing season. The main purpose of early pruning is to train a tree so it will develop a strong, well-balanced shape. When training a new tree, follow these guidelines: • As a rule, do not prune the central leader (main growing axis) unless you don’t want to keep it. Pruning the leader is appro- priate for some naturally low-branched trees or if you want to Cooperative Extension Service | Agriculture and Natural Resources | Family and Consumer Sciences | 4-H Youth Development | Community and Economic Development 158 • Care of Woody Plants CHAPTER 12 develop a multi-stemmed plant. of the tree) must have a wide angle of Trees with a central leader, such as attachment with the trunk (crotch angle). linden, sweetgum, or pin oak, may need Branches with less than a 30° angle little or no pruning except to shorten frequently break, while those with angles or head back branches competing with between 60° and 70° rarely do. the central leader. Some pruning may be • For shade trees, choose branches for necessary to maintain desired shape and major scaffolds that are at least 8 inches to shorten overly vigorous shoots. apart vertically, and preferably 20 to 24 • The height of the lowest branch can inches (Figure 1a). Closely spaced scaf- range from a few inches above the folds will have fewer lateral branches, ground for a screen or windbreak to resulting in long, thin branches with more than 12 feet above the ground for a poor structural strength. canopy. Lower limbs usually are removed • Five to seven scaffolds should fill the circle over a period of years until the desired of space around the trunk (Figure 1b). height is reached, beginning in the nurs- This arrangement prevents one limb from ery and continuing for several years after overshadowing another and reducing transplanting, competition for light and nutrients. • For greatest strength, branches selected • Remove or prune shoots that are too low, for permanent scaffolds (the framework close, or vigorous in relation to the leader and scaffold branches. Pruning Terminology Apex—The tip of a shoot. Root sucker—A shoot that arises from the Thinning—Removing an entire shoot or root system. limb where it originates. Apical dominance—The influence of a growing shoot tip on the buds and Scaffold limb—A large limb that forms the Water sprout—A long shoot that grows in shoots below it. The shoot tip produces framework of a tree. an undesirable location on a trunk or a hormones that move with gravity toward major limb. Vertical water sprouts often the earth. This chemical message pre- Shoot—One season’s branch growth. The arise on the upper side of horizontal vents growth of most lateral buds below bud scale scars (ring of small ridges) on limbs. the tip and reduces growth of lower a branch mark the start of a season’s shoots. This effect is inhibited if a branch growth. is growing horizontally. Spur—A short shoot that bears flower Bud—An undeveloped shoot, leaf, or buds and often fruit, either on the end (terminally) or sides (laterally). flower, or a combination of leaves and leader flowers, formed on the sides or ends of shoots and in leaf axils (the angle formed where a leaf joins a shoot). Collar—A swollen area at the base of a branch where it connects to a trunk. Contains special tissue that prevents decay from moving downward from the scaold limb branch into the trunk. Crotch angle—The angle formed between the trunk and a main scaffold limb. The water-sprout best angle is 45° to 60°. Head—The part of a tree from which the secondary scaold main scaffold limbs originate. Heading—Cutting off part of a shoot or limb rather than removing it entirely where it attaches to another branch. Leader—The uppermost portion of a scaf- fold limb. The terminal is the tip (apex) of crotch the leader. trunk root sucker CHAPTER 12 Care of Woody Plants • 159 Figure 1. Proper 3 4 or new growth. More flower-bearing wood is vertical spacing (a) and 3 radial spacing (b) for produced with properly timed pruning. scaffold branches. 4 Some deciduous shrubs have colored 2 bark that is attractive in winter. Because the 2 best color is produced on young wood, hard 5 pruning produces not only longer stems, 1 but also more intensely colored ones. Other plants are grown for their foliage. Proper pruning can increase the quality and 1 5 quantity of foliage produced. (a) vertical spacing (b) radial spacing Restricting Growth Over time, trees and shrubs often grow Maintaining Plant Health too big for their space, and regular pruning In pruning to maintain plant health, first is necessary to keep them in bounds. Formal consider sanitation, which includes elimi- hedges are pruned to maintain a uniform nating dead, dying, or diseased wood. Any growth rate. To reduce labor, select plants dying branch or stub could be an entry point that will not exceed their allotted space. or buildup chamber for insects or fungi that could spread to other parts of the tree. When removing wood infected with dis- Pruning Tools ease, such as a fungal canker or blight, it is important to make the cut in healthy wood Hand Shears beyond the infection. Sterilize pruning tools Hand pruning shears are good for with alcohol or a mild bleach solution after branches up to ½ inch in diameter. If you use each cut to prevent transfer of disease to them to cut larger branches, you risk mak- healthy stock. ing a poor cut and/or damaging the shears. Keeping a shrub or tree from growing too There are two styles of hand shears: densely can help prevent disease. Evergreen scissor-action (or bypass) and anvil-cut shrubs, in particular, usually benefit from (Figure 2a). Scissor-action shears have a thin, occasional thinning, which allows light and air sharp blade that slides closely past a thicker, to penetrate throughout the shrub and results but also sharp, blade. This type usually costs in even growth of healthy foliage. more but makes cleaner, closer cuts. Anvil- cut shears have a sharpened blade that cuts Improving Flowers, Fruit, against a broad, flat blade. Foliage, and Stems Lopping Shears The more flowers and fruit a plant pro- duces, the smaller they are, as is evident on Lopping shears have long handles and are an unpruned rosebush or fruit tree. Pruning operated with both hands (Figure 2b). Even reduces the amount of wood and diverts the cheapest can cut material ½ inch in diame- energy into production of larger, though pos- ter. The better ones can slice through branches sibly fewer, flowers and/or fruit. Most flower- 2 inches thick or more, depending on species ing shrubs bloom on either last year’s growth and condition. For example, pin oak wood is tougher than linden, and until decay sets in, dead wood is tougher than live wood. Figure 2. Pruning scissor-action anvil-cut shears (a) and lopping shears (b). (a) pruning shears (b) lopping shears 160 • Care of Woody Plants CHAPTER 12 Pole Pruners to 6 points.