Growing organic grapes (Vitis species) successfully depends on your climate, cultural strategies, and the varieties you choose. Arid climates provoke fewer diseases than humid climates. You can grow grapes nearly anywhere in Zones 3 through 10, and they tolerate a wide range of soil conditions; well-drained soil in the pH range of 5.5 to 7.0 is best. Grapes need full sun and very good air circulation to hamper diseases.
At least three grape species and countless varieties exist in North American gardens and vineyards. The European grape (V. vinifera) grows best in a Mediterranean climate, such as California and parts of the southwestern United States. In hotter, humid climates, many people grow muscadine grapes (V. rotundifolia), which thrive in Zones 7 through 9. The native North American species (V. labrusca) and its hybrids are the hardiest and best for most other regions of the country.
To sort out the complicated lineage, divide grapes into two broad categories: table grapes and wine or juice grapes. Table grapes have tender skins suitable for fresh eating and may contain seeds or be seedless. Wine and juice grapes may have tougher skins but plenty of sweet juice for liquid consumption or making into jelly. Ripe fruit colors range from green to pink and red to deep purplish black.
Before planting young grapes, prepare the soil thoroughly as described in the "Berry Patch Basics" section, earlier in this chapter. Install a sturdy trellis consisting of two or three heavy wires strung 24 inches apart on sturdy posts. Brace the end posts.
Several pruning and training systems exist, but the basic idea in all of them is to establish one or two main trunks per vine. Each trunk grows horizontal lateral branches, as described for kiwi (see the following section), which you attach to the wires. The flowers and fruit appear on wood that grows in the current year from the laterals that grew in the previous year. Starting in winter after the first growing season, begin the pruning and training as follows:
1. In the first winter, choose two healthy, vigorous canes to keep, and remove the rest.
Prune these main trunks back to three or four buds each.
2. The next summer, select the most vigorous shoot from each trunk, and remove competing shoots.
Train the shoots on a string until they reach the top wire; then pinch them to encourage lateral branching, as shown in Figure 15-2.
3. In the second winter, remove all growth from the trunk and lateral branches.
Cut laterals back to ten buds. Let vines grow unpruned through the summer.
4. In the third winter and subsequent years, choose the laterals for the current year, as well as replacement laterals for the next year.
Leave ten buds on the current-year laterals and two buds on the replacements. (Remember that grapes grow fruit on wood that grows in the current year from last season's laterals.) Prune off all other wood, removing as much 90 percent of the previous year's growth.
Prevalent diseases and pests include berry moth, mites, leafhoppers, and Japanese beetles, as well as Botrytis bunch rot, powdery mildew, and black rot. Some varieties are less sensitive to infection than other varieties.
Train grapes on a trellis, and prune to a main stem with lateral branches.
Grape varieties often grow best in specific regions of the country. Consult your local extension office or reputable nursery for recommendations. Also take a look at the "Surfing for small fruits" sidebar in this chapter.
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