Horticulture Principles and Practices

19.6 STRATEGIES FOR PRUNING ABOVEGROUND
PLANT PARTS
19.6.1 BASIC PRUNING PRACTICES AND TERMINOLOGIES
As previously indicated, cutting is the primary activity in pruning. Cutting permanently
removes plant parts to accomplish a desired objective. Vegetative material can be
removed in one of two basic ways, each with distinct effects on the plant. Entire shoots
or limbs can be removed by thinning cuts. Alternatively, parts (terminal parts) of a shoot
or limb can be removed by heading cuts. Thinning cuts open up the canopy for ventilation,
light penetration, and other benefits. Removing the terminal parts of shoots by
heading affects auxin movement through the plant. Groups of lateral buds are stimulated.
Horizontal limbs tend to produce vertical shoots called water sprouts.
The major tree branches extending from the trunk are called scaffold branches.
They define the tree’s outline and hence its canopy shape. Removing a scaffold branch
hence has the potential to alter the shape of the canopy. The central stem is the trunk,
while the junction between the trunk and scaffold branch is the crotch. The main growing
point of the tree (the tip end of the trunk) is called the leader or terminal. Removing
the leader alters the shape of the tree.
19.6.2 PRUNING DECIDUOUS TREES
There are several approaches to pruning trees, the most common being crown thinning,
crown raising, and crown reduction (Figure 19–8).
1. Crown thinning. The principal objective of thinning is to open up the plant canopy
for light to penetrate to lower branches for better fruit set and increased productivity.
Without adequate light, shaded branches become unproductive but nonetheless use
up nutritional resources available to the plant. In thinning, the operator strategically
removes certain branches, such as those that are inward growing. The operation
involves limited or no trimming at all so that the general shape of the plant is
preserved. To avoid stress to the plant, no more than 25 percent of the crown should
be removed at any time. The limbs are evenly spaced on the stem, and the low and
unproductive ones are removed. Thinning is a common orchard management
practice for keeping fruit trees in the best shape for high productivity.
2. Crown raising. In crown raising, the lower one-third of the branches of a tree are
removed. This pruning approach is used to develop stems for timber production.
In residential areas, crown raising provides clearance for pedestrians, vehicles,
and building.
3. Crown reduction. Also called drop crotch pruning, crown reduction is used to reduce
the height of a tree. Trees growing under utility lines are cut back to avoid contact
with lines, some of which carry electricity. It has the potential to alter the natural
appearance of the tree and hence is considered a pruning method of last resort by
some experts. Furthermore, it is used on trees with pyramidal growth forms. Growth
reduction is accomplished by pruning back the leaders and branch terminals.
19.6.3 PRUNING FLOWERING SHRUBS
1. Rejuvenation. Rejuvenation pruning is a severe method of pruning in which all the
canes of a shrub are cut back to about 6 inches above the ground (Figure 19–9).
This method is applied when a shrub has outgrown its allocated space or stopped
flowering. It is done in late winter before plants start their spring growth. Such a
severe cutback may cause a plant to miss a cycle of blooming while it regrows.
2. Renewal Pruning. Renewal pruning is employed to rejuvenate old plants by removing
old, unproductive branches, which allows for fresh and vigorous replacement growth.
Flowering shrubs may be rejuvenated in this way. Fruit trees in the landscape
Thinning
Removal of excess
vegetative growth to open
the plant canopy and
reduce the number of
fruiting branches for larger
fruits.
19.6 Strategies for Pruning Aboveground Plant Parts 577