Some Principles Of Pruning

Leaving the shaping of the plant out of consideration and having in
mind pruning proper, all efforts in pruning are directed toward two
objects: (1) The production of leafy shoots to increase the vigor of
the plant. (2) The promotion of the formation of fruit-buds. The
first, in common parlance, is pruning for wood; the second, pruning
for fruit.

Pruning for wood.

Some grapes, in common with varieties of all fruits, produce excessive
crops of fruit so that the plants exhaust themselves, to their
permanent injury and to the detriment of the crop. Something must be
done to restore and increase vegetative vigor. The most natural
procedure is to lessen the struggle for existence among the parts of
the plant. The richer and the more abundant the supply of the food
solution, the greater the vegetative activity, the larger the leaves
and the larger and stouter the internodes. Obviously, the supply of
food solution for each bud may be increased by decreasing the number
of buds. The weaker the plants, therefore, the more the vine should be
cut. The severe pruning in the first two years of the vine's existence
is an example of pruning for wood. The vine is pruned for wood in the
resting period between the fall of leaf and the swelling of buds the
following spring.

Pruning for fruit.

Growers of all fruits soon learn that excessive vegetative vigor is
not usually accompanied by fruitfulness. Too great vigor is indicated
by long, leafy, unbranching shoots. Some fruit-growers go so far as to
say that fruitfulness is inversely proportionate to vegetative vigor.
There are several methods of diminishing the vigor of the vine; as,
withholding water and fertilizers, stopping tillage, the method of
training and by pruning. Pruning is used to decrease the vigor of the
vine, in theory at least, for the practice is not always so
successful, by pruning the roots or by summer-pruning the shoots.

Root-pruning the grape at intervals of several years is a regular
practice with some varieties in warm countries, Europe more
especially, but is seldom or never practiced in America except when
planting and when roots arise from the cion above the union of stock
and cion.

Summer-pruning to induce fruitfulness consists in removing new shoots
with newly developed leaves. These young shoots have been developed
from reserve material stored up the preceding season, and until they
are so far developed that they can perform the functions of leaves
they are to be counted as parasites. When, therefore, these shoots are
pruned or pinched away, the plant is robbed of the material used by
the lusty shoot which up to this time has given nothing in return. The
vigor of the plant is thus checked and fruitfulness increased.
Summer-pruning may become harmful if delayed too long. The time to
prune is past with the grape when the leaves have passed from the
light green color of new growth to the dark green of mature leaves.

Fruit-bearing may be augmented by bending, twisting or ringing the
canes, since all of these operations diminish vegetative vigor.
Ringing is the only one of these methods in general use, and this only
for some special variety or special purpose, and usually with the
result that the vigor of the vine is diminished too much for the good
of the plant. Ringing is discussed more fully in Chapter XVI.

The manner of fruit-bearing in the grape.

Before attempting to prune, the pruner must understand precisely how
the grape bears its crop. The fruit is borne near the base of the
shoots of the current season, and the shoots are borne on the wood of
the previous year's growth coming from a dormant bud. Here is
manifested one of Nature's energy-saving devices, shoot, leaves,
flowers and fruit spring in a short season from a single bud. In the
light of this fact, pruning should be looked on as a simple problem to
be solved mathematically and not as a puzzle to be untangled, as so
many regard it. For an example, a problem in pruning is here stated
and solved.

A thrifty grape-vine should yield, let us say, fifteen pounds of
grapes, a fair average for the mainstay varieties. Each bunch will
weigh from a quarter to a half pound. To produce fifteen pounds on a
vine, therefore, will require from thirty to sixty bunches. As each
shoot will bear two or three bunches, from fifteen to thirty buds must
be left on the canes of the preceding year. These buds are selected in
pruning on one or more canes distributed on one or two main stems in
such manner as the pruner may choose, but usually in accordance with
one or another of several well-developed methods of training. Pruning,
then, consists in calculating the number of bunches and buds necessary
and removing the remainder. In essence pruning is thinning.

Horizontal versus perpendicular canes.

An old dictum of viticulture is that the nearer the growing parts of
the vine approach the perpendicular, the more vigorous the parts. The
terminal buds, as every grape-grower knows, grow very rapidly and
probably absorb, unless checked, more than their share of the energy
of the vine. This tendency can be checked somewhat by removing the
terminal buds, which also helps to keep the plants within manageable
limits, but is better controlled by training the canes to horizontal
positions. Grape canes are tied horizontally to wires to make the
vines more manageable and to reduce their vigor and so induce
fruitfulness; they are trained vertically to increase the vigor of the
vine.

Winter-pruning.

Winter-pruning of the vineyard may be done at any time from the
dropping of the leaves in the autumn to the swelling of the buds in
the spring. The sap begins to circulate actively in the grape early in
the spring, even to the extremities of the vine, and most
grape-growers believe this sap to be a "vital stream" and that, if the
vine is pruned during its flow, the plant will bleed to death. The
vine, however, is at this season of so dropsical a constitution that
the loss of sap is better denominated "weeping" than "bleeding." It is
doubtful whether serious injury results from pruning after the sap
begins to flow, but it is a safe practice to prune earlier and the
work is certainly pleasanter. The vine should not be pruned when the
wood is frozen, since at this time the canes are brittle and easily
broken in handling. On the other hand, it is well to delay pruning in
northern climates until after a heavy freeze in the autumn, to
winterkill and wither immature wood so that it can be removed in
pruning.

Summer-pruning.

There are three kinds of summer-pruning, the removal of superfluous
shoots, heading-in canes to keep the vines in manageable limits and
the pruning to induce fruitfulness discussed on a foregoing page,
which need not have further consideration. It is very essential that
the grower keep these three purposes in mind, especially as there is
much dispute as to the necessity of two of these operations.

All agree that the vine usually bears superfluous shoots that should
be removed. These are such as spring from small, weak buds or from
buds on the arms and trunk of the vine. These shoots are useless,
devitalize the vine, and hinder vineyard operations. A good practice
is to rub off the buds from which these shoots grow as they are
detected, but in most vineyards the vines must be gone over from time
to time as the shoots appear. Still another kind of superfluous
shoots, which ought to be removed as they appear, are those which grow
from the base of the season's shoots, the so-called secondary or
axillary shoots. These are usually "broken out" at the time the shoots
from weak buds are removed.

While there is doubt as to the value of heading-back the vine in the
summer for the sole purpose of inducing fruitfulness, there can be no
doubt that it is desirable for the purpose of keeping some varieties
within bounds. Heading-back is not now the major operation it once
was, the need of severe cutting being obviated by putting the vines
farther apart, by training high on three or even four wires and by
adopting one of the drooping systems of training. The objections to
heading-back in the summer are that it often unduly weakens the vines,
that it may induce a growth of laterals which thicken the vines too
much, and that it delays the maturing of the wood. These bad effects,
however, can be overcome by pruning lightly and doing the work so late
in the season that lateral growths will not start. Most vineyardists
who keep their plantations up find it necessary to head back more or
less, depending on the season and the variety. The work is usually
done when the over-luxuriant shoots begin to touch the ground. The
shoots are then topped off with a sickle, corn-cutter or similar tool.

Next: Renewing Fruiting Wood
Previous: Pruning And Training Distinguished

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