- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6550) Unit Title: PRUNING ____________________________________________________________________________ (CLF6554) Topic: TECHNIQUES OF MAKING Time Taught in Year(s) PRUNING CUTS 2 hours 3 and 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (J-2) - Explain six methods for pruning trees and shrubs (e.g., thinning, heading back, drop crotch, topping). Special Materials and Equipment: Pruning equipment, trees and shrubs to use for practice pruning References: Editors of Ortho Books. (1989). ALL ABOUT PRUNING. Available from: Ortho Books, P.O. Box 5047, San Ramon, CA 94583. Editors of Sunset Books and Sunset Magazine. (1990). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Harris, Richard W. (1983). ARBORICULTURE: CARE OF TREES, SHRUBS, AND VINES IN THE LANDSCAPE. Englewood Cliffs, NJ: Prentice-Hall. Evaluation: Quiz by instructor TOPIC PRESENTATION: TECHNIQUES OF PRUNING TREES AND SHRUBS The way a plant responds to pruning cuts depends on the basic principles of plant growth. Taking these principles into consideration enables a person to prune with more skill. A. The Role of the Bud 1. Almost all new growth on trees and shrubs develops from buds on the branches. There are 3 types of buds: dormant, latent, and adventitious. a. Dormant buds form during one growing season and remain dormant until the next growth season when they grow into stems, leaves, or flowers. 1) Dormant buds at the branch tip are called terminal buds; new stems arise first here. 2) Dormant buds on the side of a branch are called lateral buds; side branches develop here. a) Lateral buds at the base of a leaf are called axillary buds; some of them produce leaves or flowers. b. Latent buds are dormant buds that remain inactive for many seasons; they remain at or near the surface of the bark as the branch grows. 1) Latent buds (as well as dormant buds) are strongly linked to the stem's pipeline of water and nutrients. 2) Latent (and dormant) buds are the plant's insurance; if a branch is cut or broken above such buds, new shoots can grow quickly. 3) Some plants produce latent buds which can easily produce new shoots; other plants must rely mainly on visible dormant buds to produce new growth. c. Adventitious buds develop where no buds previously existed. They sometimes grow after a branch is injured or pruned back to mature tissue. 1) Adventitious buds differ from latent buds in that they develop close to the branch surface and are not strongly connected to the trunk or branch. 2) These weakly attached buds are easily broken for several years; the formation of annual growth rings gradually strengthens their connection. 3) The ease with which plants produce adventitious buds differs among species. B. Apical Dominance 1. Apical dominance is the dominance of the bud at the tip of a branch (the terminal bud) and the simultaneous inhibition of the growth of lateral buds behind the terminal bud. a. Apical dominance is controlled by a hormone in the terminal bud known as auxin. b. Auxin suppresses the growth of other buds, signalling them to remain dormant. 2. This hormonal effect determines a plant's branching pattern and its response to pruning. a. As long as the terminal bud remains alive, it will be the first to grow in the spring. b. If the terminal bud has been cut off by pruning, side buds will be free to develop, and the growth patterns of the plant will be drastically altered. 3. Skillful pruning lies in understanding and manipulating bud growth. a. Pruning off a terminal bud releases dormant, latent, or adventitious buds from the growth inhibition caused by apical dominance. This alters the plant's natural growth patterns. b. Pruning off a stem or side branch to where buds have already broken dormancy and formed side shoots preserves the plant's natural growth patterns. C. The Technique of Making Proper Pruning Cuts 1. It is important to use proper equipment when pruning. Review CLF6553, Identification, Safe Use, and Maintenance of Pruning Equipment. a. Use hedge shears only for shearing hedges, NOT for pruning. b. Use pruning shears that are strong enough for the job. If they don't cut easily through a branch, they are too small, too dull, or both. Switch to a pair of lopping shears or use a pruning saw instead. c. Hold scissor-type pruning shears so that the thin cutting blade is next to the main stem; this results in the cleanest, closest cut. d. Be sure pruning equipment is sharp; clean cuts callus over faster than cuts with ragged edges. e. When pruning diseased or infested plants, clean and sterilize pruning equipment after use. 4. Limbs larger than 1 inch in diameter must usually be cut with a saw. a. When pruning small branches with a pruning saw, hold the branch in one hand and use the other to cut along the slanting outside edge of the collar. b. Make saw cuts with an upstroke to avoid injuring bark in the crotch between the trunk and branch. 5. Branches much larger than 2 inches in diameter should be cut in 3 steps to avoid splitting the branch and tearing the bark. a. Make the first cut (the undercut) on the bottom of the branch, 12-24 inches from the branch attachment. This cut should be made until the saw starts to bind, about 1/3-1/2 way through the branch. b. Make the second cut (the removal cut) all the way through the the branch, starting from the top. Start the cut a few inches farther out from the attachment than the undercut was made. c. Make the final cut just beyond the outer portion of the branch collar or branch bark ridges, to remove the remaining stub. 2. The first principle to keep in mind when making pruning cuts is this: Never leave a stub. Another way of stating this principle is: Always make a cut just above some sort of growth (a bud or a stem). a. A correct pruning cut has its lowest point even with the top of the growth bud, and the cut slants upward at about the same angle as the remaining branch or bud. Cut on a slant about 1/4 inch above the bud. If the cut is too close, the bud may die; if it is too far away the resulting stub will die. b. A pruning cut heals best if the branch is cut from the trunk just along the outer edge of the branch collar where the plant's wound-healing chemicals are stored. This is called natural target pruning. 1) Natural target pruning minimizes damage from pruning wounds and maximizes the use of the plant's natural healing and protective capabilities. 2) If a branch is cut off flush with the parent branch or trunk--and the collar is removed as was once advised--the tree loses its natural protective barrier and decay organisms can more readily enter the wound. 3) Painting various materials on pruning cuts has not been shown to be effective. a) Exposure to the sun may crack all but the thinnest coverings. b) Moisture from rain, sprinklers, or dew can then enter the cracks and accumulate in pockets between the wood and the wound covering. c) These circumstances are even more favorable for wood- rotting organisms than an uncovered wound. 3. When removing mistletoe, cut off an affected limb at least 1 foot below the point of mistletoe attachment, preferably at the next lower crotch. a. It is particularly important to remove mistletoe before it produces seed. b. If mistletoe grows on the main branches or the trunk, so that removal would markedly damage the tree's structure or appearance, cut off the aerial part of the mistletoe. Make the cut close or treat the stub with herbicide to kill the haustoria (root-like structures) imbedded in the tree. c. Cutting out the aerial portions of mistletoe without applying an inhibitor will prevent fruiting for at least two seasons. __________________________________________________________ ACTIVITY: 1. Practice making pruning cuts on branches that have been obtained just for practice. 2. Observe the pruning practices of professional tree maintenance people. __________________________________________________________ 1/11/91 CLH/clh #%&C