- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6550) Unit Title: PRUNING ____________________________________________________________________________ (CLF6555) Topic: METHODS OF PRUNING Time Taught in Year(s) TREES AND SHRUBS 3 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: 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: METHODS OF PRUNING TREES AND SHRUBS The two basic methods of pruning are heading and thinning. A. Heading (or heading back) is cutting a currently growing or one-year-old shoot back to a bud, or cutting an older branch or stem back to a stub or a tiny twig. 1. There are several variations of heading: a. Pinching is the removal of the tip of a growing succulent shoot. b. Tip pruning is the selective heading of shoot terminals that may or may not be growing. c. Shearing is tip pruning without selecting individual branches (as when a hedge or topiary form is clipped). d. Stubbing is the term often used to describe heading a large branch or trunk. 2. Pruning a tree or shrub by heading results in a dense outer shell of weakly attached shoots. This occurs because the removal of the terminal bud results in the loss of apical dominance causing many vigorous new shoots to develop from buds directly below the cut. Also, buds lower on the branch usually do not open. 3. Heading cuts should seldom be used. a. New foliage and branches are so dense that lower leaves and nearby plants are severely shaded. b. The new shoots are weakly attached and can break off easily. c. The natural form of the tree or shrub is altered. B. Thinning (or thinning out) is cutting off a branch at its point of origin on the parent branch. 1. Thinning shrubs and trees reduces their size without stimulating unnecessary bushy new growth. 2. Thinning produces a more open and stronger branching pattern. More light will penetrate a thinned plant and foliage will grow more deeply inside it. 3. The plant's response to thinning is new growth distributed more evenly throughout the plant than when the plant is headed. C. There are several specific pruning practices that are commonly used on mature, large trees. 1. Crown cleaning or clearing out is the removal of dead, dying, diseased, crowded, or weak branches and watersprouts from a tree crown. 2. Crown thinning and reduction is the selective removal of branches to increase light penetration and air movement in the crown of the tree. a. Increased light and air stimulates and maintains interior foliage which in turn improves branch taper and strength. b. Crown thinning also reduces wind resistance and weight; this makes the tree better able to withstand winds and storms without major damage. 3. Drop crotching is used to reduce the overall size of a tree, while maintaining its natural shape. a. Dramatic thinning cuts are made to remove many of the major branches where they divide into secondary branches; the main trunk, scaffolds, and lateral branches are all cut back. b. Thin each to the next lower crotch, where the branch divides from the parent stem. 1) The size of the remaining branch should be two thirds or more the diameter of the branch removed so it can establish apical dominance. 2) If the drop crotch is made to a branch that is too small, the cut reacts like a heading cut and results in many dense, weak shoots emerging below the cut. c. To drop crotch an entire tree, start from the top and work down, exercising care to preserve the natural shape of the tree. 4. Crown restoration is pruning to improve the structure and appearance of trees that have been topped or severely pruned by heading cuts. a. One to three sprouts or main branch stubs should be selected to reform a more natural appearing crown. b. Selected vigorous sprouts may need to be thinned to a lateral. c. Restoration may require several prunings over a number of years. 5. Crown raising is pruning to remove the lower branches of a tree in order to provide clearance for buildings, vehicles, pedestrians, or views. a. A tree should have at least half of its foliage on branches that originate in the lower two thirds of its crown. b. This ensures a well-formed, tapered structure and uniformly distributes stress within a tree. c. When pruning for a view, it is better to develop "windows" through the foliage than to severely raise or reduce the crown. __________________________________________________________ ACTIVITY: 1. Observe trees in urban and residential areas and consider whether they are properly pruned. 2. If the observed trees are either unpruned or improperly pruned, determine what pruning methods and cuts should be recommended. __________________________________________________________ 1/11/91 CLH/clh #%&C