ho101care of woody plants mg chapter 17.pdf

HO-101 Care of Woody Plants 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 Richard Durham, consumer horticulture Extension specialist and state Master...

HO-101 Care of Woody Plants 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 Richard Durham, consumer horticulture Extension specialist and state Master Gardener coordinator, University of Kentucky.. Reasons for Pruning In this chapter: Reasons for pruning can be grouped into four general Reasons for Pruning 01 categories: Training a plant Pruning Terminology 02 Maintaining plant health Pruning Tools 03 Improving the quality of flowers, fruit, foliage, and stems Basic Pruning Techniques 04 Restricting growth Espaliering 06 Training a Plant Shade Trees 06 Prune trees and shrubs after transplanting only to remove dead, Fruit and Nut Trees 06 broken, crossed, or pest-infested branches. Contrary to common Shrubs 12 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 Hedges 13 pruned, nursery-grown plants. According to research, excessive Rose Bushes 14 pruning at transplanting reduces plant size and does not aid in survival. Vines and Groundcovers 14 However, pruning should begin during a tree’s first growing For More Information 14 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: T o prune or not to prune? This is a question that often As a rule, do not prune the central leader (main growing faces gardeners. Most feel they ought to prune but are axis) unless you don’t want to keep it. Pruning the leader is not sure why or how. Pruning is an accepted practice in appropriate for some naturally low-branched trees or if you orchards and frequently is done in rose gardens, but it is used want to develop a multi-stemmed plant. haphazardly elsewhere. Ornamentals are most often pruned Trees with a central leader, such as linden, sweetgum, or only when a shrub or tree begins to encroach on its neighbors, pin oak, may need little or no pruning except to shorten or a walkway, or a building. head back branches competing with the central leader. Some Pruning often is thought of as a way to make a barren tree pruning may be necessary to maintain desired shape and to fruitful. If carried out correctly, it eventually will do so. However, shorten overly vigorous shoots. years of neglect cannot be corrected in one season. Gardeners The height of the lowest branch can range from a few inches who don’t know how to prune but do so because they think they above the ground for a screen or windbreak to more than should often end up with no flowers at all, because they either 12 feet above the ground for a canopy. Lower limbs usually prune excessively or prune at the wrong time of the year. Keep are removed over a period of years until the desired height is in mind that pruning will not compensate for lack of fertiliza- reached, beginning in the nursery and continuing for several tion, poor weed control, or drought conditions. years after transplanting, What, then, is pruning? Why, when, and how should it be For greatest strength, branches selected for permanent scaf- done? Pruning can be described as the removal of part of a folds (the framework of the tree) must have a wide angle of woody plant for a specific purpose. This chapter explains the attachment with the trunk (crotch angle). Branches with less reasons for pruning, the proper techniques and tools to use, than a 30° angle frequently break, while those with angles and how to prune various types of plants. between 60° and 70° rarely do. For shade trees, choose branches for major scaffolds that are at least eight inches apart vertically, and preferably 20 to 24 inches (Figure 17.1a). Closely spaced scaffolds will have fewer lateral branches, resulting in long, thin branches with poor structural strength. CHAPTER 17 Care of Woody Plants Pruning Terminology 3 3 33 4 4 44 3 3 Apex—The tip of a shoot. 33 Apical dominance—The influence of a growing shoot tip on the buds and 4 4 shoots below it. The shoot tip produces hormones that move with 2 2 44 gravity toward the earth. This chemical message prevents growth of 22 most lateral buds below the tip and reduces growth of lower shoots. 2 2 This effect is inhibited if a branch is growing horizontally. 22 5 5 Bud—An undeveloped shoot, leaf, or flower, or a combination of 1 1 55 leaves and flowers, formed on the sides or ends of shoots and in leaf 11 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 down- 1 1 5 5 11 55 ward from the branch into the trunk. Crotch angle—The angle formed between the trunk and a main scaffold (a)(a) vertical spacing vertical spacing (b)(b) radial radial spacing spacing limb. The best angle is 45° to 60°. (a)(a) vertical spacing vertical spacing (b)(b) radial radial spacing spacing Head—The part of a tree from which the main scaffold limbs originate. Figure 17.1. Proper vertical spacing (a) and radial spacing (b) for scaf- fold branches. Heading—Cutting off part of a shoot or limb rather than removing it entirely where it attaches to another branch. Five to seven scaffolds should fill the circle of space around Leader—The uppermost portion of a scaffold limb. The terminal is the tip (apex) of the leader. the trunk (Figure 17.1b). This arrangement prevents one limb from overshadowing another and reduces competition for Root sucker—A shoot that arises from the root system. light and nutrients. Scaffold limb—A large limb that forms the framework of a tree. Remove or prune shoots that are too low, close, or vigorous Shoot—One season’s branch growth. The bud scale scars (ring of small in relation to the leader and scaffold branches. ridges) on a branch mark the start of a season’s growth. Spur—A short shoot that bears flower buds and often fruit, either on Maintaining Plant Health the end (terminally) or sides (laterally). In pruning to maintain plant health, first consider sanitation, Thinning—Removing an entire shoot or limb where it originates. which includes eliminating dead, dying, or diseased wood. Any Water sprout—A long shoot that grows in an undesirable location on a dying branch or stub could be an entry point or buildup chamber trunk or a major limb. Vertical water sprouts often arise on the upper for insects or fungi that could spread to other parts of the tree. side of horizontal limbs. When removing wood infected with disease, such as a fun- gal canker or blight, it is important to make the cut in healthy leader wood beyond the infection. Sterilize pruning tools with alcohol or a mild bleach solution after each cut to prevent transfer of disease to healthy stock. Keeping a shrub or tree from growing too densely can help prevent disease. Evergreen shrubs, in particular, usually benefit from occasional thinning, which allows light and air to penetrate scaffold limb throughout the shrub and results in even growth of healthy foliage. water-sprout Improving Flowers, Fruit, Foliage, and Stems The more flowers and fruit a plant produces, the smaller they secondary scaffold are, as is evident on an unpruned rosebush or fruit tree. Pruning reduces the amount of wood and diverts energy into production of larger, though possibly fewer, flowers and/or fruit. Most flowering shrubs bloom on either last year’s growth or new growth. More flower-bearing wood is produced with properly timed pruning. crotch Some deciduous shrubs have colored bark that is attractive trunk in winter. Because the best color is produced on young wood, root sucker hard pruning produces not only longer stems, but also more intensely colored ones. Other plants are grown for their foliage. Proper pruning can increase the quality and quantity of foliage produced. 17-2  Care of Woody Plants CHAPTER 17 scissor-action anvil-cut (a) pruning shears (b) lopping shears Figure 17.2. Pruning shears (a) and lopping shears (b). Restricting Growth Hedge Shears Over time, trees and shrubs often grow too big for their Manual hedge shears have long, flat blades and relatively space, and regular pruning is necessary to keep them in bounds. short handles, one for each hand (Figure 17.4). Heavy-duty Formal hedges are pruned to maintain a uniform growth shears with one serrated blade are good for difficult jobs. rate. To reduce labor, select plants that will not exceed their Power hedge shears also are available. For home use, electric allotted space. models are most common. Pruning Tools Saws Many makes and models of hand pruning saws are available Hand Shears (Figure 17.5). Fineness of the cutting edge is measured in points Hand pruning shears are good for branches up to one-half (teeth per inch). Average saws are about 5½ to 6 points. Use an inch in diameter. If you use them to cut larger branches, you risk 8-point saw for delicate, close work on small shrubs and trees making a poor cut and/or damaging the shears. and a 4½-point saw for fairly heavy limbs. There are two styles of hand shears: scissor-action (or bypass) If a saw suddenly folds while in use, it can injure the opera- and anvil-cut (Figure 17.2a). Scissor-action shears have a thin, tor’s fingers. Folding saws have either a slotted-head holding sharp blade that slides closely past a thicker, but also sharp, screw or a wingnut that secures the saw blade open or closed. blade. This type usually costs more but makes cleaner, closer A fixed-blade saw with a leather scabbard is safer. cuts. Anvil-cut shears have a sharpened blade that cuts against a broad, flat blade. Lopping Shears Lopping shears have long handles and are operated with both hands (Figure 17.2b). Even the cheapest can cut material one-half inch in diameter. The better ones can slice through branches two Figure 17.3. Pole pruner. inches thick or more, depending on species and condition. For example, pin oak wood is tougher than linden, and until decay sets in, dead wood is tougher than live wood. Pole Pruners manual Pole pruners have a hooked blade above and a cutting blade electric beneath (Figure 17.3). The blades are on a pole and are operated by pulling down a long piece of cord. The poles can be in sections, which either fit together or manual electric telescope. They can be made of several materials. Poles made Figure 17.4. Hedge shears. of fiberglass or a plastic compound probably are best. Wooden poles are heavy. Aluminum poles are light but can conduct electricity if they touch an overhead wire. Poles can be fitted with saws, but saws are usually frustrat- pruning saw ing to use. bow saw Pole pruners can be dangerous. Material that is cut overhead pruning saw can fall on the operator unless it hangs up in other branches. Be careful and wear head and eye protection when using bow saw these tools. Figure 17.5. Saws. 17-3 CHAPTER 17 Care of Woody Plants Saw blades can be either straight or curved. Many people Thinning removes undesired wood (Figure 17.6b). In thin- prefer a curved blade that cuts on the draw stroke. A double- ning, a branch or twig is cut off at one of the following places: edged saw has fine teeth on one side, is coarse on the other, and Its point of origin from the parent stem is difficult to use in densely branched plants. A lateral side branch Bow saws are good only where no obstruction exists for 12 The “Y” of a branch junction inches or more above the area to be cut. Ground level Chainsaws come in a variety of sizes, both gasoline and electric. However, in general, chainsaws are not appropriate for Thinning results in a more open plant and does not stimulate pruning live plant material. They are better suited to removing excessive new growth. By thinning, you can remove consider- trees and cutting firewood. able growth without changing the plant’s natural appearance or growth habit. Thus, you can maintain plants at a given height Caring for Tools and width for years while allowing room for side branches to grow. Clean and oil tools regularly by wiping an oily cloth on blades and other surfaces. Several passes with a good oilstone usually suffice. Keep cutting edges sharp. Paint or varnish wooden Twigs and Small Branches handles or regularly treat them with linseed oil. When pruning twigs and small branches, always cut back to Use tools properly. Don’t twist or strain pruners or loppers. a vigorous bud or an intersecting branch. Keep the branch to be cut as deeply in the jaws and near the When cutting back to a bud, choose a bud that is pointing in pivot as possible. Don’t use pruning tools to cut wires. the direction that new growth is desired. Be sure not to leave a stub over the bud or cut too close to the bud. When cutting back to an intersecting (lateral) branch, choose Basic Pruning Techniques a branch that forms an angle of no more than 45° with the one There are only two types of cuts: heading cuts and thinning to be removed and has a diameter of at least one-half that of cuts. Figure 17.6 shows the effect of each. the branch to be removed (Figure 17.7). Heading involves cutting off part of a shoot or limb (Figure Make slanting cuts when removing limbs that grow upward; 17.6a). It increases the number of new shoots and stiffens this technique prevents water from collecting in the cut and branches, holding them in position. speeds up healing. (a) branch size good (a) heading but angle too great. (a) branch size good but angle too great. 45˚ (b) 45˚ (b) (b) angle good but branch tootoo small. (b) angle good but branch small. (a) (a) (b) thinning (c) (c) (c) angle good and branch diameter at least one-half that of branch to be removed. Figure 17.6. Heading cuts (a) increase the number of new shoots Figure 17.7. Proper branch selection. formed and stiffen the branches, holding them in position. Thinning cuts (b) reduce the number of new shoots and direct growth. (c) angle good and branch diameter at 17-4 least one-half that of branch to be removed.  Care of Woody Plants CHAPTER 17 Thick, Heavy Branches Roots Remove thick, heavy branches flush with the collar at the After several years, a tree may develop long roots running 15 base of the branch, not flush with the trunk (Figure 17.8). The to 25 feet or more away from the trunk. These roots, along with collar contains chemically protected tissue. When a dead many branched side roots, physically support the tree. Most of branch decays naturally, the decay advances downward until the small feeding roots that gather nourishment branch off the it meets this internal protected zone. When it reaches this area main roots far from the trunk. of very strong wood, the branch falls away. The remaining small If a tree is balled and moved, most of its feeding roots are zone of decayed wood is walled off within the collar. If a branch’s cut off, so the tree may die when transplanted. For this reason, collar is removed, the protective zone is lost, causing a serious nursery growers root-prune plants to force them to grow new trunk wound that wood-decay fungi can easily infect. feeding roots near the trunk. These new roots are included in Removing the collar causes injury whether the pruned the balling operation and ensure growth after transplanting. branch is living or dead. To safely move a small tree or shrub, root-prune it a year For more than 50 years, the recommended method of prun- or so before digging it. In the fall, sever half of the roots to one ing was to cut flush with the trunk and paint. These recom- foot deep by forcing a sharp spade into the soil around the mendations have no basis in scientific fact. The flush cut, by plant, leaving a shovel width of untouched soil between cuts. damaging the collar, increases a tree’s injury. Painting merely Make the circle of cuts slightly smaller than the size of the ball hides the wound and makes the person doing the pruning feel you’ll eventually dig. The next spring, sever the other half of the that he or she has done something to “help” the tree. In fact, roots. Move the tree that fall. Another way to accomplish the paints or wound dressings may trap moisture and increase same thing is to cut all the roots on one side in the spring, cut disease problems. the other side the following spring, and move the plant that fall. The proper method for cutting branches larger than 1½ Recent research indicates that most new roots grow from inches in diameter is shown in Figure 17.9: the ends of pruned roots. Therefore, you must dig a root ball 1. Undercut the bottom of the branch about one-third of the four to six inches larger than the root-pruned area to get the way through, six to 12 inches out from the trunk (Figure newly developed roots. 17.9a). If there is danger of the branch damaging lower limbs Cutting the roots in a circle early in the spring, as explained or objects on the ground, rope it and support it. above, sometimes forces a tree, shrub, or vine to bloom the 2. Make a second cut from the top, about three inches farther following year. out from the undercut, until the branch falls away (Figure Root pruning also is used to force a vigorously growing fruit 17.9b). If you roped the branch for support, carefully lower tree, wisteria vine, or flowering dogwood into bloom. it to the ground after the second cut. 3. Cut back the resulting stub to the branch collar (Figure 17.9c). branch collar (b) (a) correct (c) incorrect Figure 17.8. Remove branches flush with the collar, not flush with the Figure 17.9. Pruning a large branch: (a) Undercut one-third of the trunk. way through the branch. (b) Cut through from the top until the branch falls away. (c) Cut back to the collar. 17-5 CHAPTER 17 Care of Woody Plants Espaliering Repeat this process during the next two seasons, at which time a total of eight scaffolds, four on each side of the trunk, Many gardeners prune for decorative purposes. Numerous should be firmly established. Bend the leader to form one of the training systems are based on the art of espalier, which origi- top scaffolds, rather than cutting it off at the top wire. By the end nated in France and Italy about 400 years ago. Some are quite of the fourth season, fruit trees should be producing heavily. elaborate and require considerable time and patience as well In following years, do all pruning during spring and summer. as detailed knowledge of the plant’s growth characteristics. When new spring growth is about two inches long, cut it off. Others are relatively simple. Remove about one-fourth of the previous season’s growth. Do An espalier system can separate yard areas and produce not prune the scaffolds’ terminals. a large volume of high-quality fruit in a limited area. Fruit About August 1 or as soon as new growth reaches 10 to 12 trees trained in this fashion should be on dwarfing rootstock. inches in length, cut it back to two or three buds. Repeat about Otherwise, they tend to grow too large. a month later, if necessary. This pruning encourages flower The easiest espalier system is a horizontal cordon (Figure bud formation and prevents vigorous growth from getting out 17.10). Apples, pears, plums, and some shrubs, such as pyracan- of bounds. tha, adapt well to this system. The plant usually is supported by a wall, fence, or wire trellis. Training to a four-tier cordon or four-wire trellis is relatively easy. Shade Trees You can construct a simple four-wire trellis using two eight- Young shade trees may not need much pruning to develop foot posts. Space the posts 12 feet apart and set them two feet a good framework. Mature trees generally are pruned only for in the ground. Run wires through the posts at heights of 18, 36, sanitation, safety, or size restriction. 54, and 72 inches. Plant two unbranched whips of the desired You can prune shade trees at any time of the year. Late-winter plant six feet apart between the two posts. pruning often is preferred because it is easy to shape a tree when Before growth begins the first spring, cut off each whip just foliage is gone. Also, fewer precautions are necessary to avoid above the highest bud that is below the lowest wire. Three or garden and flower bed damage, and cleanup is easier. A few more shoots should develop near the cut. Retain the uppermost trees, such as sugar maples, birches, black walnuts, and flower- shoot and develop it as the central leader. Train the other two ing dogwoods, bleed profusely when pruned in late winter. The as main scaffold branches along the lower wire, one on each bleeding is unsightly but is not harmful. side of the central stem. Remove all other growth. Summer pruning may be more effective in directing plant Tie the two scaffold shoots loosely to the wire as soon as they growth. It also may cause fewer suckers or water sprouts to are 10 to 12 inches long. Use twine, plastic chain link ties, or grow. (A water sprout is a long, vigorous shoot that grows in other suitable material. Tie the shoots so they are nearly hori- an undesirable location on a trunk or major limb.) zontal. This arrangement reduces vegetative vigor and induces flower bud formation. If you tie the end of the shoot below horizontal, however, growth at the end will stop and vigorous Fruit and Nut Trees shoots will develop along the upper side. The basic objectives in directing and guiding the growth of By the end of the first season, the lateral branches should be young fruit trees are to encourage early fruit production and established on the lower wire, and the central leader should have develop an optimum tree structure for supporting future crops. grown above the second wire. At the end of the first winter, while You can meet these objectives by maintaining a proper bal- the plant is dormant, cut the central leader back to a bud just below ance between vegetative and potential fruiting wood. Pruning the second wire. Choose two scaffold branches to tie to the second of mature trees is aimed at producing new growth of fruiting wire and allow the central leader to grow above the third wire. wood. This section discusses pruning of various types of fruit and nut trees. first winter second winter Figure 17.10. Training a tree with an espalier system. 17-6  Care of Woody Plants CHAPTER 17 Nonbearing Apple Trees They should be evenly distributed and not directly above one another. Vertical spacing between scaffolds can vary from three Avoid excessive pruning of young, nonbearing trees, because to 12 inches, depending on the ultimate size of the tree. Remove it stimulates excessive shoot growth and delays fruiting. Instead, shoots developing below the lowest desired scaffold (18 to 24 prune to train young trees by redirecting limbs, stimulating inches above ground). branching where desired, and removing growth that is in an undesirable location. To minimize winter injury, do not prune young, nonbearing apple trees before February 1. (a) Pruning of a mature apple tree is greatly affected by early training, so it’s imperative that training begin early. Waiting three or four years after planting results in a poorly developed, weak tree. Correcting such a problem, usually with heavy prun- ing, only further delays and decreases fruit production. (c) An integral part of tree training is limb spreading. There are two reasons for limb spreading: To develop limb orientation at 60°From vertical, thus balanc- (b) ing vegetative and fruiting growth To develop strong, wide crotch angles (greater than 35°) Limb orientation affects vigor in various ways, as shown in Figure 17.11. Possible limb orientations: (a) vertical; (b) horizontal; (c) 60°From vertical. The 60° limb is ideal. Figure 17.11. Upright or vertical limbs (Figure 17.11a) produce their longest shoots near their tip and tend to have high vegeta- bark inclusion tive vigor. Often, fruits hang down against these limbs and rub against them. On the other hand, horizontally oriented limbs (Figure 17.11b) develop vigorous water sprouts along their upper surface at the expense of potential fruiting spurs. The ideal limb orientation is about 60°From vertical. These limbs (Figure 17.11c) have less vigorous shoots near the tip, more uniform branching, and more fruiting spurs. Fruits hang down from the limb and are less prone to rub. Another reason for limb spreading is to develop strong crotch (a) (b) angles (Figure 17.12a). Wide crotch angles are strong. Many cul- tivars, such as Red Delicious (particularly spur types), naturally Figure 17.12. Strong, wide crotch angle (a) and narrow crotch angle develop narrow crotch angles. If these crotch angles are not with bark inclusion (b). widened to greater than 35°, a condition called bark inclusion can develop (Figure 17.12b). In this condition, bark is trapped between the trunk and scaffold, and layers of annual wood are prevented from growing together. Splitting may occur at these narrow crotch angles. 3 At Planting 2 Training begins at planting. Early pruning forces the growth of lateral branches from which you’ll select future scaffolds. When planting, cut back spur-type and semidwarf apple 3–12" 1 2 trees to a height of 30 to 35 inches. Cut back standard trees to 40 inches. If the tree is branched, head it back to a strong bud to stimulate growth of the central leader. Head back and retain 18–24" desirably located branches for scaffolds. Remove undesirable 1 3 side branches. First Growing Season (a) vertical scaffold (b) horizontal scaffold Scaffold selection can begin in summer, especially on culti- placement (side view) placement (top view) vars that develop narrow crotch angles. Generally, in the first Figure 17.13. Selecting well-spaced scaffolds. Scaffolds should be year, you can select two to four good scaffolds (Figure 17.13). spaced 3–12 inches apart vertically (a) and as equally as possible around the trunk (b). 17-7 CHAPTER 17 Care of Woody Plants Spread or remove limbs with crotch angles of less than 35°. maintains vigor in the center top of the tree while maintaining In early summer, while shoots are soft, it’s easy to spread limbs. desired tree height. Place a clothespin or short piece of wood with a notch in one end between the trunk and the shoot. Use the notch to push Bearing Apple Trees the shoot outward. Weigh down the shoot with a light weight, Mature apple trees often need to be pruned vigorously to such as a fishing weight. Remove undesirably located shoots encourage new growth of fruiting wood. To bear fruit, spurs at this time. must be at least two years old. After several years of production, First Dormant Season however, they lose vigor. If you haven’t yet selected shoots to retain as scaffolds, do Good fruiting wood requires both moderate vigor and so now. Spread selected scaffolds before doing any pruning, exposure to good light. since spreading changes the shape of the tree and may influence Fruiting may be poor if vigor is too high or too low. Too-high pruning decisions. Next, remove shoots that you didn’t select vigor can be the result of inadequate fertilization, no pruning, as scaffolds. Head the central leader to maintain dominance excessive cropping, or shading of fruiting wood. Too-low vigor and induce branching; cut it back three to five inches above the can be because the bearing wood is shaded, which can result point where you want the next tier of scaffolds. in small, poorly colored fruits. Scaffolds usually do not need to be headed; generally shoots branch naturally in their second season (Figure 17.14). All you need to do is spread the scaffolds to encourage uniform first year branching. However, a scaffold often exhibits excess vigor and upsets the balance of a tree’s growth, in which case you should head it to shorten and stiffen it. You also can use heading cuts to encourage growth and branching on spur-type trees. second year Second Growing Season Limbs not previously trained can be spread easily early in the growing season, when wood is flexible. Remove fruit develop- ing on the central leader to maintain vigor in the tree’s center. Select and train the new tier of scaffold limbs, choosing limbs Figure 17.14. Natural branching of a shoot. that are well spaced in relation to lower scaffolds. Second Dormant Season Again, spread scaffolds before pruning. Some of the first-year scaffolds may have turned upward and resumed vertical growth. Use longer spreaders to spread them back to the desired orienta- tion. Move the smaller spreaders farther up into the tree. Head cut the central leader to maintain vigor and stimulate branching. Succeeding Years Continue training and pruning following the principles of Figure 17.15. Shorten limbs with thinning cuts. central leader dominance and proper scaffold selection and training. Keep scaffolds at a 60° angle from vertical. Maintain a conical tree shape, with upper branches shorter than lower ones. Always prune the top portion of the tree more heavily than the lower. After the third year, you can shorten upper scaffolds with thinning cuts (Figure 17.15), which remove an entire shoot or branch at its junction with a lateral scaffold or trunk. Thinning cuts are less invigorating than heading cuts. They also improve light penetration and can redirect a limb’s growth. cut Remove crossing branches, vigorous water sprouts, shoots next year’s cut growing up into the tree, and shaded hanging branches. Once the tree is as tall as you want, cut it back each year to a weak lateral on the central leader (Figure 17.16). This practice Figure 17.16. Prune to a lateral to maintain height. 17-8  Care of Woody Plants CHAPTER 17 Good light exposure is necessary for development of flower Use thinning cuts to maintain good light exposure in the buds as well as fruit of optimum size, color, and sugar content. canopy. Make moderate cuts throughout the tree to distribute A typical tree canopy is composed of different layers or zones vigor and provide good light penetration. Use heading cuts only in terms of light exposure (Figure 17.17): where branching is desired or vigor is low. The outside zone of leaves and fruit (a), which receives a high Another problem with overly dense trees is that spray pen- proportion of direct light. This zone receives more light than etration is reduced and problems such as scale may develop needed for good growth and fruiting. in the dense areas. In this situation, make many thinning cuts The middle zone (b), which receives adequate light throughout the tree, especially in the upper, outer portions. The inner zone (c), which receives inadequate light and is This procedure will open up the tree canopy and reestablish unproductive good tree shape. The relative proportion of these zones is influenced by tree When pruning mature trees, also remove the following: size and shape. As tree size increases, the percentage of the tree Drooping or low-hanging branches (or prune them to a that is shaded and unproductive increases (Figure 17.18). Trees lateral that is positioned above horizontal—see Figure 17.20) with wide tops and narrow bottoms also have a high percentage Crossed, dead, diseased, or damaged limbs of shaded area (Figure 17.19). Water sprouts, unless some are needed to develop new fruiting wood (a) more than adequate light Keep the following precautions in mind when pruning bearing trees: Avoid pruning terminal shoots back to horizontal branches (b) adequate light (often called a bench cut, Figure 17.21). Such cuts result in weak limbs and an umbrella shape that encourages water sprouts. (c) inadequate light Figure 17.17. Light distribution zones in a large apple tree. semidwarf semistandard standard (12' tall) (16' tall) (20' tall) 3% shaded 19% shaded 24% shaded Figure 17.18. The shaded area increases as tree size increases. Figure 17.20. Thin out low-hanging branches. (a) bench cut (b) proper cut Figure 17.19. Tree shape influences shaded areas. Figure 17.21. Bench cuts (a) and proper cuts (b). 17-9 CHAPTER 17 Care of Woody Plants Remove no more than one or two large limbs per year. If a When trees are mature, use thinning cuts to improve light lot of pruning is required, spread the process over a two- or penetration. Do the heaviest pruning in the treetop. Remove three-year period. In the one or two years before and after upper horizontal branches so they won’t shade the rest of the heavy pruning, reduce or eliminate nitrogen application, tree or produce excess water sprouts. depending on soil type, tree variety, and your experience. Do not head back trees after their framework has been The excessive vigor that can result from severe pruning can developed. Doing so encourages the tree to sprout soft terminal decrease fruit quality. The effect is much the same as from shoots, which are highly susceptible to fire blight. excessive nitrogen application. It may include excessively large, poorly colored, soft apples that do not store well. Peach and Nectarine Trees Vegetative growth competes with fruit for calcium; thus, To train young trees in a vase shape, head back young peach under conditions of excessive vigor, cork spot or bitter pit or nectarine trees to 18 to 30 inches at planting time, depend- may develop due to calcium deficiency in the fruit. ing on how much room you want under the tree. Choose two Use heading cuts only to maintain tree size when trees are or three scaffold branches evenly spaced around the tree. Head at or near the desired size. Such pruning often is used in an the selected scaffolds to three to six inches and remove all other attempt to reduce tree size, but misuse of this technique can side shoots (Figure 17.22a). In the first summer, pinch unwanted disrupt vigor and reduce yield so much that it takes several shoots in order to direct most of the growth into the scaffolds. years for the tree to recover. Heading, especially of one-year- old shoots, induces masses of shoots to grow close to the In the first dormant season, head the scaffolds 24 to 30 inches away from the trunk (Figure 17.22b). The result will be cuts. These abundant shoots can shade and weaken inner stiff scaffolds with strong secondary limbs. Thin all vigorous areas of the tree. shoots that compete with the secondary scaffolds. Invigoration from pruning is, in part, a nitrogen response. During the second dormant season, select three or four Pruning alters the balance between the treetop and secondary scaffold limbs 12 to 18 inches above the primary root system. Removing part of the treetop increases the scaffolds (Figure 17.22c). amount of nitrogen available for the remaining growing In the third dormant season, thin the fruiting wood. Keep the points. Always combine a pruning program with a good more outward-growing wood for better sunlight penetration. fertilization program. Once the scaffold system is established, prune as little as possible until the tree begins to bear. Remove all strong, upright Pear Trees shoots growing in the center of the tree, and lightly head Train pears to have multiple leaders with three to five main back terminal growth on the scaffolds to outward-growing scaffold branches. Avoid excessive pruning of young trees, laterals. The result will be an open-center (vase-shaped) tree except to stimulate scaffold development. (Figure 17.23). (a) (a) (a) (c) (c) (b)(b) (c) (b) Figure 17.22. Pruning to a vase shape: (a) At planting time, head the tree about 18 to 30 inches above ground. Choose two or three scaffold branches and head the selected scaffolds to three to six inches. (b) In the first dormant season, head the scaffolds 24 to 30 inches away from the trunk. Thin all vigorous shoots that compete with the secondary scaffolds. (c) During the second dormant season, select three or four Figure 17.23. A vase-shape tree has an open center and outward- secondary scaffold limbs 12 to 18 inches above the primary scaffolds. growing branches. 17-10  Care of Woody Plants CHAPTER 17 Pruning Bearing Trees When planting a cherry tree, head the tree about 18 to 24 Peach and nectarine trees bear fruit on the previous season’s inches above the ground. Head all shoots to 24 to 36 inches after wood. Yearly pruning ensures good fruit production. the first and second year’s growth. Remove the terminal buds During the dormant season, prune to counteract the tendency of short shoots in order to promote branching (Figure 17.24). of fruiting wood to move away from the trunk in an upward and In the third and fourth years, head the most vigorous shoots. outward direction. The procedure is as follows: When the tree begins to bear fruit, remove all but seven or Remove shoots that fruited the previous year. eight scaffold branches. Head all shoots in the dormant season Cut back to shoots of moderate vigor. to develop a low, spreading tree that is easy to manage. Remove strong-growing shoots in the treetop by thinning Established trees require minimal pruning. Lightly thin out them to more upright shoots. new shoots and cut out weak wood and interfering branches. Thin out the weakest shoots. Sour Leave shoots well spaced for good light penetration. Prune out dead and diseased wood, particularly that with If a sour cherry tree has no strong branches at the time of cankers or severe oozing. (Peach and nectarine trees are planting, head it to about 24 inches above the ground. Select notorious for their susceptibility to disease.) laterals when growth begins the second year. If the tree has some good laterals when planted, remove In mid to late summer, head back the upper, outer shoots those lower than 16 inches from the ground. Select about three in order to allow better light distribution throughout the tree. permanent scaffold limbs along the leader, four to six inches Again, prune out dead or diseased wood. apart and not directly above one another. Do not head them back, since doing so tends to stunt terminal growth. In following years, select side branches until there are five or Plum Trees six scaffold limbs well distributed along three to four feet of the To train trees into a vase shape, head plum trees at 18 to 24 main stem above the lowest branch. Then modify the leader by inches at planting. The following year, select three or four main cutting to an outward-growing lateral. shoots to be scaffold limbs. If the scaffold crotch angles are narrow, After fruiting begins, pruning consists mainly of annually spread them to 45° to 60° using clothespins or wooden sticks with thinning out excessive and crowded growth to allow sunlight notches in the ends. Remove the rest of the shoots with thinning into the tree and renew fruiting wood. Sour cherries bear mostly cuts, then head the selected scaffolds at 2 to 2½ feet from the crotch on two- to five-year-old spurs. to stimulate branching into secondary scaffolds. In the third dormant season, thin third-year scaffolds to one or two per secondary scaffold. In Japanese plums, thin interior shoots to spread the tree. Pruning Bearing Trees Prune European prune trees to lighten the ends of heavily bearing branches to prevent breakage. Cut back annual shoot growth, being careful not to cut away long-lived fruiting spurs. These trees bear on one-year-old shoots as well as older ones. Fruiting limbs tend to arch under the fruit load. Water (a) untrained (b) properly trained sprouts arise from the upper side of these limbs. To renew fruit- ing wood, cut back to the arch and thin water sprouts. Those sprouts remaining will become fruiting wood. On Japanese plum trees, thin one-year-old shoots, but leave enough to renew fruiting wood. Thin out a few branches that have old, weak spurs. Cherry Trees Sweet Train sweet cherry trees to the modified leader system rec- ommended for apple trees. Give special attention to selecting (a) untrained (b) properly trained scaffold limbs with wide crotch angles. Sweet cherry trees are Figure 17.24. Training a cherry tree: (a) Without proper training, this subject to winter injury, often splitting where limbs join the sweet cherry tree is too tall and sparsely branched. (b) Heading all main stem. It is essential to develop crotch angles as widely as shoots of a young sweet cherry tree produces more branches and a possible to ensure a strong framework. lower tree. 17-11 CHAPTER 17 Care of Woody Plants Shrubs growth (Table 17.1). Prune them soon after they bloom so there is time for vigorous summer growth, which provides flower Prune both evergreen and deciduous shrubs in late buds for the following year. Some shrubs that bloom after June winter before new growth starts. Minor corrective prun- do so from buds that are formed on that spring’s shoots (Table ing can be done at any time. Specific pruning situations are 17.2). Prune these shrubs in late winter to promote vigorous discussed below. spring shoot growth. Deciduous Evergreen When deciduous shrubs are planted bare-root, some prun- Most evergreen trees and shrubs are sold B&B or in a con- ing may be necessary. Lightly prune roots if any are broken, tainer. Unlike deciduous shrubs, they require little pruning at damaged, or dead. Prune branches by thinning (not shearing) planting time. to reduce overall plant size by one-half or more. Balled and burlapped (B&B) or container shrubs require little Table 17.1. Shrubs that bloom on last season’s growth. if any pruning. Occasionally, branches are damaged in transit; Botanical name Common name remove them at the time of planting. Prune only to develop Cercis chinensis Chinese redbud desired size and shape. Chaenomeles japonica Japanese quince Pruning for most mature deciduous shrubs consists of thin- ning, gradual renewal, and rejuvenation. Chionanthus virginicus Fringe tree Thinning cuts are used to maintain a shrub’s desired height Daphne spp. Daphne and width (Figure 17.25). Thin out the oldest and tallest stems Deutzia spp. Spring-flowering deutzia first. Use hand pruning shears, loppers, or a saw rather than Exochorda racemosa Pearlbush hedge shears. Forsythia spp. Forsythia Gradual-renewal pruning involves annually cutting a few of Kerria japonica Kerria the oldest and tallest branches back to slightly above ground Lonicera spp. Honeysuckle level (Figure 17.26). Some thinning may be necessary to shorten Magnolia stellata Star magnolia long branches or maintain a symmetrical shape. Philadelphus spp. Mockorange To rejuvenate an old, overgrown shrub, remove one-third Pieris spp. Andromeda of the oldest, tallest branches at or slightly above ground level Rhododendron spp. Azalea and rhododendron before new growth starts. Rosa spp. Rambling rose Time pruning of flowering shrubs to minimize disruption Spiraea spp. Early white spirea of blooming. Spring-flowering shrubs bloom on last season’s Syringa spp. Lilac Viburnum spp. Viburnum Weigela florida Old-fashioned weigela Table 17.2. Shrubs that bloom on the current season’s growth. Botanical name Common name Abelia x grandiflora Glossy abelia Buddleia davidii or globosa Butterfly bush before thinning after thinning Callicarpa japonica Japanese beauty bush Figure 17.25. Thinning a shrub. Caryopteris x clandonensis Bluebeard Ficus carica Fig Hibiscus syriacus Shrub althea Hydrangea arborescens Hills of snow Hydrangea paniculata Peegee hydrangea Hypericum spp. St. Johnswort Lagerstroemia indica Crape myrtle Rosa spp. Bush rose Spiraea bumalda Anthony Waterer spirea Spiraea japonica Mikado spirea before pruning after pruning Symphoricarpos Coralberry and snowberry Figure 17.26. Gradual renewal of a shrub. (Dark branches in left-hand illustration are removed.) Vitex agnus-castus Chaste tree 17-12  Care of Woody Plants CHAPTER 17 Thinning out is the best way to prune most mature ever- What can be done with a large, overgrown, bare-bottomed, green shrubs. Some evergreens can be sheared to achieve and misshapen hedge? If it is deciduous, the answer is fairly a stiff, formal appearance. However, you’ll still need to thin simple. In spring, before leaves appear, prune to one foot below them occasionally. the desired height. Then trim carefully for the next few years to give it the shape and fullness desired. Occasionally, hedge plants in very poor shape do not recover from this treatment Hedges and must be replaced. Hedges are plants set in a row so they merge into a solid lin- Rejuvenating evergreen hedges is more difficult. As a rule, ear mass. They have been used for centuries as screens, fences, evergreens cannot stand severe pruning. Arborvitae and walls, and edgings. A well-shaped hedge is no accident. It must yew are exceptions. Other evergreen hedges may have to be trained from the beginning. be replaced. Establishment of a deciduous hedge begins with the selec- tion of nursery stock. Choose young trees or shrubs one to two Tools feet high, preferably with multiple stems. Cut the plants back Traditional scissor-action hedge shears are the best all- to six to eight inches to induce low branching. Late in the first around tool for trimming hedges. They cut much better and season or before bud break in the second, prune off half the closer than electric trimmers, which often break and tear twigs. new growth. The following year, again trim off half. Electric trimmers do poorly on large-leafed and wiry-twigged In the third year, start shaping. Trim to the desired shape varieties, and sometimes jam on thick twigs, but hand shears before the hedge grows to the desired size. Once it reaches its work on any type of hedge. Hand shears also are quieter and mature size, it will be too late to achieve maximum branching less likely to gouge the hedge or injure the operator. at the base. Do not let lower branches be shaded out; trim so Hand pruners are useful for removing a few stray branches the base of the hedge is wider than the top (Figure 17.27). After and are essential if you want an informal look. Use loppers the hedge reaches the desired dimensions, trim frequently in and/or a pruning saw to remove large individual branches. order to maintain its size. Chainsaws are not recommended for use on hedges. Evergreen nursery stock for hedging need not be as small as deciduous material and should not be cut back when planted. Trim lightly after a year or two. Start shaping as the individual Rose Bushes plants merge into a continuous hedge. Do not trim too closely, All rose bushes need some type of pruning. If they are not because many needle-bearing evergreens do not easily generate pruned for several years, they deteriorate in appearance, often new growth from old wood. develop more than the usual disease and insect problems, Hedges often are shaped with flat tops and vertical sides and produce smaller and smaller flowers. Proper pruning and are sometimes conical in shape (Figure 17.28a and b). This unnatural shaping seldom is successful. The best shape, as far as the plant is concerned, is a natural form—a rounded or slightly (a) good (a) good shape;shape; base base (b) poor (b) shape; poor shape; weak weak growthgrowth pointed top with sides slanting to a wide base (Figure 17.28c gets sun getsand rain rain sun and at base at base and d). This shape aids in shedding snow, which otherwise can break branches. Also, by trimming the top more narrowly than the bottom, you enable sunlight to reach all of the leaves. Before shaping a hedge, think about the plants’ natural shape. Figure 17.27. Correct (a) and incorrect (b) hedge pruning. E.g., common buckthorn, a spreading plant, is easily shaped to a Roman arch (Figure 17.28c). Naturally conical arborvitae does particularly well in a Gothic arch shape (Figure 17.28d). Two questions often arise: “How often should this hedge be trimmed?” and “When should I trim?” Answers depend on the kind of shrub, the growing season, and the degree of neatness (a) snow(a) snow (b) straight (b) straight lines lines require require(c) peaked (c) peaked and and(d) rounded (d) rounf you desire. accumulates accumulates moremore frequent frequent trimming trimming rounded rounded top top whichwhich followfo on broad, on broad, flat flat hinders hinders snowsnow tendency, tendencreq In general, trim before new growth begins to shade lower top top accumulation accumulation less thinning less thin leaves. Trim slow-growing plants such as boxwood when new growth is more than three or four inches long. Yews, for example, may need shearing only once annually. Shear faster growing evergreens before new growth exceeds a(a)foot. snow Laurel (b) straight (a) snow (b) straight lines require lines require(c) peaked (c) peaked and and(d) rounded (d) rounded forms,forms, and photinia may need to be sheared every fouraccumulates to six weeks moremore accumulates frequent frequent trimming trimming roundedrounded top top whichwhich followfollow nature’s nature’s on broad, on broad, flat flat hindershinders snowsnow tendency, tendency, require require during spring and early summer. top top accumulation accumulation less thinning less thinning Figure 17.28. Improper (a and b) and proper (c and d) hedge shapes. 17-13 CHAPTER 17 Care of Woody Plants encourages new growth from the base, makes the plant healthy and attractive, and results in large blossoms. Hybrid tea, grandiflora, and floribunda roses require annual pruning in the spring after winter protection is removed. As a guideline, prune roses when the forsythia blooms. If you prune too early, frost injury may make a second pruning necessary. For small pruning jobs, the only tools necessary are sharp hand-pruning shears and gloves. Use loppers to reach in and (a) correct (a) correct (b) incorrect (b) incorrect cut out large, dead canes. A small saw with a pointed blade can Figure 17.29. Proper pruning angle (a) and improper angles (b). also be helpful. Remove all dead and diseased wood by cutting at least one inch below the damaged area. Remove all weak shoots and those Large-flowering Climbers growing toward the center. If two branches rub or are close Climbing roses have large flowers, more than two inches enough that they will rub soon, remove one of them. On old, across, borne on wood that is two or more years old. Canes are heavy bushes, cut out one or two of the oldest canes each year. larger and sturdier than those of ramblers. Some flower only Cut back the remaining healthy canes. The height to which once in June, but some, called everblooming climbers, flower a rose should be cut depends on the cultivar. The average prun- more or less continuously throughout the summer. ing height for floribundas and hybrid teas is between 12 and Prune these roses in autumn, any time before cold weather 18 inches, but taller growing hybrid teas and most grandifloras sets in. First cut out dead and diseased canes. Next, remove may be left at two feet. one or two of the oldest canes at ground level to make room for Make cuts at a 45° angle above a strong outer bud (Figure new canes. Shorten laterals (side shoots) by three to six inches 17.29). Aim the cut upward from the inner side of the bush after flowering. If the plant is strong, keep five to eight main to push growth outward and promote healthy shoots and canes and tie them to a trellis, fence, wall, or other support. If quality flowers. the canes are not strong, keep only a few. Some types of roses have special pruning considerations, as discussed below. Vines and Groundcovers Standard or Tree Roses Pruning procedures for ornamental vines are similar to those for ornamental shrubs. Be sure to prune flowering vines at the A tree rose is a hybrid tea, grandiflora, or floribunda budded right time. Prune those that flower on new wood before growth at the top of a tall trunk. Prune tree roses like hybrid teas, cut- begins in spring. Prune those that flower on last season’s growth ting the branches to within six to 10 inches of the base of the immediately after flowering. budded top in order to encourage rounded, compact, vigorous Prune vines that are grown for foliage to control growth and new growth. direction. Timing is less critical than for flowering vines. Groundcover plants require very little pruning. Remove Miniature Roses dead or damaged stems whenever you notice them. Some Miniatures are six to 12 inches high, with tiny blooms and trailing groundcovers, such as English ivy, may need pruning foliage. They do not need special pruning. Cut out dead, dis- to prevent encroachment on lawn areas or other plants. The eased, and weak growth and remove the hips. appearance of St. Johnswort, a woody, yellow-flowered ground- cover, is improved by trimming it back every three or four years in early spring. For large plantings, a lawn mower set to cut three Ramblers to four inches above the crowns makes fast work of this job. Old-fashioned rambler roses have clusters of flowers, each usually less than two inches across. They often produce pliable canes 10 to 15 feet long in one season. Ramblers produce best For More Information on one-year-old wood, so this year’s choice blooms come on See the following publications from the UK Cooperative last year’s growth. Prune immediately after flowering. Remove Extension Service: some of the large, old canes. Tie new canes to a support for the Pruning Landscape Trees (HO-45) next year. Pruning Landscape Shrubs (HO-59) Revised 01-2024