Horticulture Principles and Practices

spreading or bending affects shoot growth and development. If too wide (e.g., 90 degrees),
water sprout growth is stimulated. These shoots should be pruned. Narrower crotches
(about 30 degrees) slightly suppress terminal growth while increasing the number and
length of side branches. Moderate angles (45 to 60 degrees) have an intermediate effect
between the narrow and wide crotches. Whenever physical support is needed, tying is
often involved. Tree trunks should not be too tightly restrained to a support but allowed
some room to move in the wind. Wind movement allows the trunk to develop strength in
its wood for additional support. Wide-angled crotches encourage the development of
strength in the wood of the limb and thereby improve its resistance to damage from the
weight of fruits or snow accumulation. Narrow-angled crotches are prone to damage
because of weakness resulting from the formation of bark inclusions (Figure 19–20).
19.14.1 TRAINING SYSTEMS FOR FRUIT TREES
Pruning and training of fruit-bearing trees are done together to increase productivity
and ease harvesting and other operations. These practices start early in the growth
of plants, a strategy that prevents young trees from overbearing too early, an event
that adversely affects plant structure and productivity later in life (see chapter boxed
reading.)
19.14.2 TRELLIS TRAINING SYSTEM
Trellis training involves tying limbs of plants to wires strung between posts or constructed
against a wall or fence. Materials for tying range from wires to masking tape and
should be of a material that will not damage the limbs. Common trellis training systems
are described in the following sections.
Espalier
A training system in which
the tree or shrub is made
to grow flat against a wall
or on a trellis, often in
formal branch patterns.
Espalier
The goal of espalier training is to create a work of art confined to a specific space; as
such, it requires heavy pruning to control shoots on top of horizontal limbs. The tree
forms produced are usually two dimensional since frequently a wall or fence provides
the background of the trellis. All designs require some support system, at least in the
formative training. When forming espaliers, one should take into account the species and
the vigor of the plant. The space between horizontal limbs, for example, is wider for
peach trees (20 to 24 inches or 50.8 to 61 centimeters) than for apple trees (12 inches or
30.5 centimeters). About three tiers of limbs are adequate for small plants, but vigorous
plants can have more. All bending should be done when the limbs are still flexible. A balance
should be maintained between limbs on either side of the central axis by keeping
opposite limbs at each tier equal in length. The limbs should be tied snugly to the support
or trellis, as already mentioned. Espaliers may be formal or informal in design.
FIGURE 19–20 Development
of bark inclusion occurs when a
branch angle is too narrow. It
results in the development of
weak crotches.
Bark inclusion
Narrow
branch angle
598 Chapter 19 Pruning