Pruning grapes

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The bearing habit of Grape vines is such that pruning annually is really necessary. The fruit is produced on shoots which originate from canes which grew the preceding year.

  • Trunk is the chief stem of the vine.
  • Arms are the parts of the vine which are two or more years old, excluding the trunk.
  • Canes are one-year-old shoots. Shoots grow from these and bear fruit. The following year they are called canes.
  • Head is the area on the trunk from which arms and canes are produced.
  • Spur is a cane which has been cut back to one or two buds.

There are several types of Grapes grown for their fruits, including Vitis vinifera (European Grape), V. labrusca (Fox Grape), and V. rotundifolia (Muscadine Grape).

Grapes may be grown on a trellis, pergola, or arbor, as part of a pleached allee, or they may be trained to make a canopy over a patio to enable the owner and his friends to sit in the shade of the vines. Commercial vineyardists use a trellis consisting of posts, 8 or 9 feet long, 6 to 8 inches in diameter at the butts, set about 20 feet apart, standing about 6 feet above the ground. These are put 2 feet 6 inches or 3 feet deep.

Remove bark from the posts and treat them with copper naphthenate (Cuprinol) or creosote to retard decay. The posts are connected by two galvanized wires, No. 9 or No. 10, stretched tightly (use a wire stretcher, obtainable from horticultural-sundries men), one 30 to 36 inches from the ground and the other 30 inches above the first wire. The end posts must be braced firmly, preferably by the method indicated by the sketch.

The wire is put once around an end post and fastened securely. It is run along the windward side of the posts, which are set approximately 20 feet apart, and when stretched and fastened at the other end it is stapled to the intervening posts. These intermediate posts can be sharpened and driven into the soil. If the soil is so stony that they can't be driven into it, you will have to use a posthole digger.

The staples are driven in so that there is room for the wire to slide whenever it is necessary to tighten it. It should be attended to annually when frost gets out of the ground in the spring. At this time the posts, which probably have been partially heaved from the ground as a result of freezing and thawing, can be driven in with a maul.

Supporting the end poets of a wire trellis Two methods of supporting the end poets of a wire trellis. The one on the left is usually preferred because it does not have any wires extending beyond the post. The one on the right uses a "deadman," consisting of a log of decay-resistant wood about 2 feet by 6 inches with a No. 9 wire wound once around its midriff, or a rock of similar size and shape can be used. A hole 2 feet by 2 1/2 feet deep is dug and the log or rock buried in it.

The above method is primarily utilitarian. Grapes can be used to furnish arbors or they may be espaliered. The vines should be trained fanwise on one or both sides of the structure alternating with vines grown to a single trunk. Pruning of the fan-trained sections consists of cutting back old canes that have produced fruits and replacing them with new ones started from spurs left for that purpose the preceding year.

The single trunk, when it reaches the top of the arbor, is cut back to form a head, from which a number of canes will be produced. These are trained fanwise to cover the top of the arbor and provide fruiting shoots. Or it can be continued as a single trunk which is spur-pruned.

Pruning depends in part on the variety and in part on the system of training. The vinifera types for the most part are grown in California and are commonly pruned in such a way that the plant is self-supporting, the large head containing many spurs; or they can be trained using a modification of the following system. In the varieties of V. labrusca, of which the best known is Concord, the favourite system of training is the Kniffin, either the four-cane Kniffin or the two-cane Umbrella Kniffin. Start with a one-year-old vine rooted from a cutting the preceding year.

The plants are set in the soil 8 or 10 feet apart as early as possible in the spring and each one is cut back to a single cane, which in its turn is cut back to leave only two or three buds. During the first season the plants are allowed to sprawl along the ground at will.

The second year the vine is again cut back, leaving only the strongest cane, which is cut to leave only two buds.

The third year the strongest cane should be long enough to reach the top wire of the trellis, where it is tied (this will be the trunk). Two of the next-strongest canes are tied left and right to the lower wire and shortened. During the following growing season two strong shoots from the tip of the trunk are trained along the top wire, left and right; some fruit may be expected from the canes on the lower wires.

The fourth-year pruning will be that accorded the mature vine. Four canes will be selected to carry the fruit, one right, one left, on each of the arms. These should be cut back to leave from 25 to 60 buds, depending on the vigour of the vine. In addition, four canes are cut to spurs as near as possible to the trunk.

Umbrella Kniffin. In this system of training the trunk is carried up to the top wire and two strong canes are selected, one right and one left, plus four cut-back spurs close to the head of the vine. The canes are placed over the top wire and carried down to the lowermost, where it is tied. If sufficiently vigorous, it may be taken up to the top wire again and tied.

The practice of weighing the prunings of one-year-old wood to determine the number of buds to leave is on the increase in New York State. For an example of how the practice works, see the table below, taken from Cornell Extension Bulletin 805, New York State College of Agriculture, Ithaca, New York.

Number of buds to leave for fruiting weight

Weight of cane pruning
Concord & Delaware
Fredonia
Catawba
Less than 1 pound
Less than 30
Less than 40
Less than 25
1 pound
30
40
25
2 pounds
40
50
35
3 pounds
50
60
45
4 pounds
60
70
55
More than 4 pounds
60+
70+
55+

 

Pruning grapes A Concord vine as it may look in the fall or winter before its annual pruning.
Being pruned according to the Kniffin system The same vine after being pruned according to the Kniffin system. The support wires are 30 and 60 inches above ground level.
Before pruning Detail of the drawing of the Concord vine before pruning: T—trunk; A—arm, two-year wood; C—cane, one-year wood.
Detail of the drawing of the Concord vine after pruning: C—renewal cane, tied to wire; S—spur, one-year cane cut back to two buds; T—trunk.
One-year and two-year vines after pruning One-year and two-year vines after pruning. On the latter, five buds on each top cane, four on lower.
In bloom In bloom: T—trunk; B—shoot, current season; C—cane; F—flower cluster; S—spur with strong shoot for the following year's cane.

Sometimes it is necessary to rejuvenate a neglected vineyard. We had such a one on our place. The vines were disentangled and laid out on the ground to see plainly the kind of material we had to deal with. The first step was to get rid of the oldest, gnarly trunks.

Then enough comparatively young material was cut back severely and tied to the trellis, remembering that the shoots grown from canes that were produced the preceding year are the ones that bear fruit. The following fall we got enough grapes to make a few quarts of juice. The next year we had plenty of grapes for eating and juice. We had to call on friends to help us use up the crop from a row fifty yards long.

Muscadine Grape is valuable in the Deep South. It is not hardy in the North. The fruit is produced in "bunches" containing only two or three grapes. They can be harvested by shaking the vines and picking up the grapes from the ground. Pruning is similar to that of the Concord types except that, usually, more buds may be left on the canes. In home gardens they are commonly grown on an arbor which provides shade as well as fruit.