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, i 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.