- -  AGRICULTURE CORE CURRICULUM - -


(CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE

 (CLF6550)  Unit Title: PRUNING

____________________________________________________________________________
 (CLF6556)  Topic: MAJOR TREE PRUNING     Time     Taught in Year(s) 
                     SYSTEMS                2 hours        3 and 4      
____________________________________________________________________________

        Topic Objectives: Upon completion of this lesson the student will 
        be able to:

        Learning Outcome #:

          (J-4) - Explain the difference between the three major tree
                    pruning systems (i.e., open center, central leader,
                    and modified central leader).

          (J-5) - Discuss the purposes of training young trees to one of
                    the three systems (i.e., extension of productive life, 
                    ease of maintenance, and strengthening of the tree) and
                    demonstrate how to prune to establish scaffold 
                    branches.

          (J-6) - Practice pruning methods on landscaped plants.

        Special Materials and Equipment: Pruning equipment, trees to prune

        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: MAJOR TREE PRUNING SYSTEMS

A. There are three major tree pruning systems:

   1. Central Leader

   2. Open Center (or Vase)

   3. Modified Central Leader

B. These three methods are particularly applicable to fruit trees, which 
   are often included in home landscapes as ornamentals.

   1. Any area of a fruit tree that receives less than 30% full sun will
       bear a reduced crop of smaller fruit.

   2. By pruning to restrict the height and spread of the tree, branches
       and foliage can be prevented from shading the interior.

****************************************************************************
NOTE TO INSTRUCTOR: Use reference books to show illustrations and diagrams
                    of pruning systems and specific pruning techniques and
                    cuts.
******************************************************************************

C. Which pruning system is recommended for which trees?

   1. Central Leader

       a. This pruning system emphasizes one tall main trunk with tiers of 
           branches arising from it.

           1) With one main trunk, this shape can hold a heavy crop of 
               fruit and resist storm damage.

           2) The central-leader system is most often used for apple trees 
               and pear trees; it is also best for European plum cultivars.

   2. Open Center (or Vase)

       a. This system features a short trunk (about 3 feet tall) and an
           open center consisting of 3 or 4 main branches.

           1) The open-center or vase shape allows plenty of light and air
               into the tree's interior, encouraging fruit production on 
               lower branches.

           2) The open-center system is most successful for peaches and
               nectarines; it can also be used for apricots.

   3. Modified Central-Leader

       a. This system is a compromise between the central-leader and the 
           open-center systems; it features a short trunk and several tiers 
           of branches.

           1) This shape gives both strength and a sunny center.

           2) The modified central-leader system of pruning has become the 
               method of choice for both sweet and sour cherries.

D. Developing a Leader

   1. The first task is to determine which branch is or should be the main 
       leader.

       a. If several are growing upright in the center, select the most 
           vigorous or most central as the leader.

       b. Remove or shorten the competing branches to prevent the 
           formation of a split leader, which is inherently weak and 
           susceptible to breaking during storms.

   2. The greatest mistake in pruning a young tree is to remove the leader
       too soon--except if it is thinned to a lateral, which would then
       assume apical dominance.

       a. Even in trees that form multiple leaders with age, encouraging a 
           strong central leader when the tree is young results in sturdy
           branch structure later.

       b. In conifers, a distinct, dominant, central leader is critically
           important.

E. Selecting Scaffolds

   1. Select the lowest branches to be kept permanently.

   2. The permanent lateral scaffolds, the principal branches of the tree,
       should arise from the central leader.

   3. The best branches to select for main scaffolds emerge from the trunk 
       at an angle greater than 45 degrees (that is, a wide angle of 
       attachment).

       a. These branches are strongly attached to the trunk with
           connective wood and have desirably small branch bark ridges,
           which indicate naturally weak areas on a tree.

       b. With the exception of trees that have distinctly upright habits 
           (Lombardy poplar or columnar cultivars of maples, for example), 
           remove or subdue any potential scaffolds with narrow angles of
           attachment.

   4. For the strongest tree, select scaffold branches that are 18-24
       inches apart vertically (more for very large trees).

       a. Scaffold branches should be evenly distributed radially around 
           the trunk.

       b. A perfect spiral is not necessary, but branches should not grow 
           directly above one another.

         __________________________________________________________
         ACTIVITY: 
                     
         1. Demonstrate how to prune to establish scaffold
             branches.

         2. Demonstrate pruning small trees to each of
             the three systems.
         __________________________________________________________

1/11/91 CLH/clh
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