Site Selection
Grapes can be grown on a wide range of well-drained soils. Soils with poor drainage should be avoided. Raised beds may be used to provide an adequate root zone if vines are to be grown on soils with hardpan, claypan, or if shallow soil is located on top of impervious bedrock. Grapes will grow well on poor, shallow soils as long as irrigation and fertilizers are available.
Planting
Grapes should be spaced in rows 6 to 12 feet apart with vines 4 to 8 feet apart. Vines need to be planted in full sun to assure fruitfulness. Purchase healthy 1-year-old bare-root vines available from nurseries. Cuttings may also be collected from healthy vines and planted directly where the vines are to grow permanently. Soak roots for 1 to 6 hours if plants appear desiccated at planting time. For bare-root plantings, trim off any broken or damaged roots just above the point of injury. Dig the planting hole two to three times the diameter of the entire plant. Place the bare-root plant so the two buds left to grow are at the soil surface. Irrigate the plants to settle the soil around the roots at planting.
Watering
Irrigation is essential for good vine growth and grape production. Grapes will adapt to low water, but fruitfulness is reduced.
Water must be applied deeply and thoroughly to fill the root zone with water. Frequency will depend upon the soil type, the rooting depth of the vines, the depth of the soil, and the weather. Irrigating every 2 to 3 weeks is usually adequate under good soil conditions and moderate climate. Grapes may require more frequent irrigation in very hot climates in inland valleys.
Drip irrigation is an excellent method of watering. Generally, a fully trellised vine on a hot summer day in the Central Valley of California will require about 8 to10 gallons of water per day with drip irrigation. Vines that are less vigorous or untrellised will require 6 to 8 gallons per day. In Southern California, the rates should be similar to those of Central Valley climates. In areas along the coast, and in northern parts of California, the rates will be much lower.
Irrigation Tips
Avoid water stress during the period between bloom and berry softening. Fruit on the vine may succumb to cracking if the vines are allowed to dry and then wet again. Check the soil profile to be sure the plants are getting adequate water but not too much.
Pruning
The difference in pruning techniques is due to variability in fruitfulness. Cane-pruned varieties bear fruit further out on the cane, on buds numbered 4 to 12. Examples of cane-pruned varieties are 'Thompson Seedless' and 'Concord'. Spur-pruned varieties are much more fruitful and by being pruned back to a two-bud spur the vine is prevented from overcropping. For spur-pruned varieties such as 'Flame Seedless', 'Ribier', or 'Tokay', one would typically leave between 12 and 14 spur positions, depending on vine vigor. For cane varieties, leave between four and eight canes, again depending upon vigor. The more vigorous the vine, the more spurs or canes you can leave.
Thinning
Many grape varieties, especially spur-pruned varieties, require shoot and berry thinning.
Shoot thinning: When shoots reach 6 to 12 inches, thin them out so there are only two shoots to each spur or to each bud position on the cordon.
Berry thinning: The berry clusters also often need to be thinned to allow fewer but larger berries to form. Just after bloom and berry set, remove the lower third of the clusters or cut alternate side branches of the cluster.
Training
Grapes need to be trained onto a trellis in order to spread the vine and provide light to the leaves and fruit clusters. There are different training methods for grapes.
For spur-pruned varieties, a bilateral cordon method works well. For cane-pruned varieties, a head-trained method is suitable.
First- and Second-Year Pruning
Let the shoots grow out the first season, because shoots and leaves produce a strong root system for future vine development. Insert a 6-foot stake near the plant and train new growth to it by loosely tying it. Grapes can be pruned in the winter when the plants are dormant. If the first season's growth was vigorous, select a single shoot and train upright to the stake. If the first year's growth was weak, prune back the shoots to two-bud spurs and allow to grow out.
During the second dormant period, you'll begin training your vines. The goal is to establish a main trunk up the stake and establish the scaffold structure. The trunk should be headed back once it has reached the top trellis wire. As the new growth develops from the headed trunk, select two shoots that will develop into bilateral cordons for spur-pruned varieties. For cane-pruned varieties, select two to four shoots, which will become canes. Do not head them during the growing season. During the third dormant season, you'll prune by either the cane-pruned method or spur-pruned method.
Trellising
Trellis systems vary greatly for grapes depending upon the space available for growing the vine and also upon the vine's vigor. Ideally trellis systems allow light to reach the canes and fruit and are sturdy enough to support the vine.
Fertilizing
Adequate nutrition is important for high-quality grapes. Avoid excessive fertilization and rich soil, however, because they will contribute to excessive vine vigor and may reduce fruit set or fruit quality or both. This table serves as a guide only; fertilizer may rarely be needed in some aeras with rich soil.
| Element needed | Fertilizer | Amount per vine | When to apply | Comments |
|---|---|---|---|---|
| Nitrogen | Ammonium sulfate | 1 lb | Berry set stage or following bloom | Berry set occurs when berries reach 0.25 inch diameter |
| Ammonium nitrate | 0.75 lb | |||
| Urea | 0.5 lb | |||
| Mixed fertilizers | Follow label | |||
| Animal manures: poultry, rabbit, steer, cow | 5 to 10 lb 15 to 20 lb |
January or February | Poultry manure may cause zinc deficiency in light, sandy soils | |
| Zinc | Basic or neutral Zinc sulfate (52% zinc) |
0.1 lb/gal | 1 week prior to bloom or at full bloom on foliage | Don't apply after bloom |
| Potassium to compensate for deficiency | Potassium sulfate (44% K) |
Severe: 5 to 6 lb/vine Moderate: 4 lb/vine Mild: 3 lb/vine |
When deficient, apply to soil 6 inches deep, 18 inches from trunk Concentrate at vine |
irrigate after application |
Harvesting and Storing
There are grape varieties available that ripen over the entire summer season beginning in mid-July through early October. It is important to harvest as soon as possible after the fruit reaches full maturity in order to avoid pest problems. Berries should be full size. They may or may not have full color to be ripe. Ripeness of table grapes is determined by the amount of sugar in the fruit and that varies from variety to variety. Color may be accentuated by removing the leaves around the cluster prior to harvest.
Another indication of ripeness is the development of the external cuticle layer in the skin. Since the cuticle of the fruit is easily subject to damage, handle carefully during harvest. Harvest by cutting the fruit cluster rather than pulling from the vine. Cool it rapidly after harvest. For longer term storage, keep at 32° F or below but don't allow grapes to freeze. Don't allow the berries to be wet before storing. Unripe grapes will not ripen in storage.
