Soil and Drainage
Many types of soils are used for growing grapes, but they are most successfully grown on sandy or fine sandy loams with average fertility and good drainage. On soils low in fertility, grapes grow slowly and produce low yields; on extremely fertile soils, vines usually grow excessively and the crop matures late. Fine, tight soils that contain much clay are not suitable for grape production. Regardless of soil type, the drainage must be good. Impervious layers of clay or caliche closer than 5 feet (1.2 m) to the surface may cause poor drainage and salt accumulation.
Spacing
Spacing depends upon the cultivar, the training system, and the type of machinery used in the vineyard. Vinifera grapes trained to the head system are planted 7 to 9 feet (2.1–2.7 m) apart in the row, in rows 8 to 12 feet apart (2.4–3.7 m). In cordon or cane systems, vines are planted 6 to 8 feet apart (1.8–2.4 m) in the row and rows are separated 8 to 12 feet (2.4–3.7 m). The distance between rows depends on the trellis used. In commercial vineyards, adequate space must be provided for roads at the ends and sides of the vineyard and for driveways through the center of the planting to give ready access for harvesting and cultural operations. Twenty to 25 feet (6.1–7.6 m) is generally adequate for driveways.
Initial Planting
Plant cultivars in January or February and keep the roots damp until they are set. At planting, prune vines to one cane with two buds. Set the plants slightly deeper than they grew in the nursery, in holes wide enough to hold the roots without crowding. Pack soil slightly and apply 2 to 4 gallons (7.6–15.1 l) of water per plant.
Training Systems
In training a young vine, the grower wants to develop a single strong shoot with several well-placed laterals to form a permanent framework. Some of the vine's crop potential during early years is sacrificed to obtain a strong, well-shaped vine as inexpensively and as early as possible. After young vines have been pruned at planting, they are not pruned again until the following spring. Just before growth begins the second year, select the strongest cane and tie it to a stake to form a straight trunk. Remove all other canes. From this point, training depends upon the system you select. Three of the most common are the head, cordon, and cane (four-arm Kniffin is one example of a cane system).
- Head Sytem: This system is designed primarily for vinifera and a few hybrid cultivars. Set a post 2 x 2 inches or larger (5 cm x 5 cm) beside the vine. The post should be 30 to 36 inches (76–91 cm) above the ground. If the selected cane seems weak the second spring, cut it back to two buds. If it is vigorous, do not cut it back. Tie the cane and the future shoot that is to form the trunk to the post. Remove all lateral shoots. When the shoot is within 6 inches (15 cm) of the top of the post, cut off the terminal to encourage laterals to form the head. The third spring, prune the canes back to short spurs with two to five buds. Each succeeding spring, repeat this pruning procedure. As the head develops, you will have to cut out some spurs to prevent overproduction.
- Cordon System: This system is also designed for vinifera and hybrid cultivars. It requires a two-wire trellis, with the lower wire 20 to 40 inches (51–102 cm) above the ground and an upper wire 14 inches (36 cm) above the lower one to support the shoots. In vineyards under drip irrigation, an extra wire is usually placed below the first trellis wire to support the drip irrigation line. In the second spring, train the vines as you would for the head system, except head back the cane or shoot when it reaches the lower wire. Select two laterals and train them along the lower wire. The third spring, head the two canes back to about five buds each. These form the permanent arms of the cordon and should be gradually extended to a length of 18 to 24 inches (46–61 cm) each. Each spring, prune the canes or shoots that grow from the cordon back to two buds each. Remove all growth from the underside of each cordon. About five upright shoots (two buds each) should be allowed to grow on each permanent arm.
- Cane System: The four-arm Kniffin is a good cane system used for American varieties, most hybrids, and vinifera cultivars such as 'Thompson Seedless' and 4 'Black Monukka'. Install a two-wire trellis, with the lower wire 3 to 3.5 feet (90–107 cm) above the ground and the upper wire 5 to 7 feet (1.5–2.1 m) above the ground. At the beginning of the second spring, tie the cane or shoot to a stake. When the shoot reaches the lower wire, head it back to force laterals. Train two of these, one on each side of the vine, along the wire. Select an upright shoot and tie it to the stake above the lower wire. When it reaches the upper wire, head it back to force two laterals and train them along the upper wire. Weak varieties may require two years to reach the upper wire. In the third spring, shorten the four canes (arms) to four to six buds each. Avoid heavy production at this time by leaving fewer buds or by removing some flowers. In the fourth spring, select one cane growing from each of the four arms and tie these along the wires. Shorten these canes to seven to eight buds each. A strong vine could produce mature fruit from four eightbud canes. Remove all other canes from the vine except one arising from each arm. Shorten these to spurs of one or two buds each. These renewal spurs produce canes for next year's crop. Each spring thereafter, remove the old fruiting canes and all other growth except one cane and one renewal spur from each arm.
Grapevine Pruning Basics
Grapes are pruned more severely and methodically than any other fruit crop. Pruning not only controls vine growth, but sets crop load as well. Without severe, annual pruning, grape vines become tangled masses of unproductive shoots that decline in yield and quality very quickly. A considerable amount of research and time-honored practice has been devoted to vine pruning, and the following is a condensation of a considerable amount of literature.
Balanced pruning is a method of determining the severity or amount of one-year-old wood to remove. One "balances" next year's crop load with last year's vigor. It eliminates the need for fruit thinning in most cases. Early research showed that the amount of buds to be left after pruning could be determined on a simple formula that employs the weight of shoots pruned. To start, the pruner removes about 90% of previous season's growth, then bundles and weighs it (or estimates its weight). For a given grape type, about 20 buds are retained for the first lb of prunings, and 10-20 additional buds are retained for each additional pound of prunings. Placement of cuts involves the choices of spur versus cane lengths of pruned shoots, with the former a shorter stub than the latter.
Spur vs. Cane Pruning
Once the number of buds per vine is calculated, one must decide whether to leave the requisite number on several short stubs, or on just a few longer shoots. Short stubs with few buds are referred to as spurs, whereas longer pieces of one-year-old wood are referred to as canes.
Spur Pruning
All muscadines are spur pruned since they are highly vigorous and have fruitful basal buds. Spurs are 4-6" long, containing 1-4 buds. Muscadines are trained to one of the two cordon systems listed above. Spurs are spaced 6" apart on cordons, removing the weakest, thinnest shoots completely if overcrowding occurs. Spur clusters need to be thinned completely in crowded parts of the vine, allowing adjacent spurs to grow into the bare space. In general, spur pruning is for use on:
• Cultivars with fruitful basal buds (i.e., the buds at the base of one-year-old wood will produce fruit clusters instead of only leaves)
• Cultivars that are excessively vigorous
• Wine cultivars where quality is more important than quantity
Cane Pruning
Cane pruning is for use on:
• Cultivars with unfruitful basal buds (e.g., 'Thompson seedless' will not produce clusters on shoots that arise at the base of last year's wood)
• Cultivars which lack vigor or are low yielding
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