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For The Garden

Fruit of the Vine

Author: Cathy Babcock
Issue: April, 2018, Page 122
Growing grapes in the desert may be easier than you think

When contemplating cultivating fruit-bearing plants in the Valley of the Sun, grapes may not be the first thing that comes to mind. However, the juicy berries—yes, grapes are berries—are an excellent choice. Their fruit is tasty, their leaves provide lush greenery for your landscape, and the plants are well-adapted to the harsh conditions of the Phoenix metropolitan area.

When selecting grape plants to grow in Arizona, there are two types to consider: European (Vitis vinifera) and American (Vitis lubrusca). European varieties, including Thompson seedless, flame seedless, exotic, cardinal and ruby seedless, perform best in the Valley and other locations below 4,500 feet elevation. Hot summers and moderate winters suit them just fine. American grapes, such as concord, reliance, himrod seedless, Niagara and Campbell’s early, do better at higher elevations above 4,500 feet and have greater cold hardiness than their European counterparts. Because different species have different uses, from table grapes to wine grapes, and flavors, it’s also important to research which ones are best for your end goal, be it fresh fruit, raisins, juice, jelly or simply landscape greenery.

Site Preparation
Grapes are picky when it comes to their soil and site location. Their root systems can extend 3 to 4 feet into the ground, so deep soil with good drainage is essential. Avoid planting vines in low-lying basins, as they prefer good air circulation. They will also need full sun and plenty of room to grow up and outward. In order to grow outward, your plants will need some sort of support, the most common being a post with attached fencing or wires. Posts should be spaced 6 to 8 feet apart, with a vine planted at each post.

Vine Purchase
Vines are usually sold bare-root or in containers or bags. Winter is bare-root season, as vines are dormant and have not begun to sprout. Select the most robust plants, making sure the vines are pliable with no developing buds. Keep roots moist until planting time. Containerized plants are available in the spring. They should be robust with an abundance of new growth. Roots coming out of drainage holes could indicate a pot-bound plant and should be avoided. 

Planting
The best time to plant grapes is in early spring after the last frost. For bare-root plants, prune any broken roots. The planting hole should be twice as wide as the root system and at least 2 feet deep. Build a soil cone in the bottom of the hole over which you will spread the roots. If you are planting containerized grape plants, do not remove the potting soil when planting. Backfill using your native soil, making sure the vine is at the same depth as it was at time of purchase. Water in thoroughly but do not add fertilizer, soil amendments or root stimulators for the first year. You will not water again until new growth appears. Spread mulch around the vine as a top dressing.

If your vines have multiple canes—year-old shoots that have developed a visible bark layer and dropped most of their leaves—it is imperative to remove all but the most vigorous-looking one, cut the remaining cane back to two buds, and then leave the vines alone for the first summer so as to produce a strong root system for future vine development. Because grapes have a deep root system, water your plants slowly, deeply and infrequently, about every seven to 10 days. Grapes also respond well to drip irrigation. Winter water is unnecessary unless rains are scarce. Let your vines grow for at least three years before trying to harvest fruit. A fertilizer program is not necessary until about the third year, at which time you can apply 10 ounces of 10-10-10 fertilizer to each plant yearly. Double that amount at about the six-year mark.

Pests
There are two species of insect pests that cause huge problems for Arizona-grown grapes. The western grape leaf skeletonizer larvae do exactly what their name implies: They eat grape leaves, leaving the veins behind. They can be controlled with applications of
Bacillus thuringiensis (Bt) applied as a spray according to label directions. Grape leafhoppers, both nymphs and adults, suck the sap from leaves, causing the foliage to become discolored and even stunted and curled. These miniscule yellowish-green bugs can be treated with insecticidal soap, such as Safer Soap. Non-insect nuisances can also damage or destroy grape vines and fruits. A chalky white fungus, known as powdery mildew, initially appears as whitish lesions on the leaves and progresses to dark patches on canes and shoots and dead leaves; infected berries will darken and shrivel. It can be treated with a fungicide, such as sulfur. If birds become a problem, the only recourse is covering the plants with netting.

Grape vines should be trained and pruned carefully in order to produce abundant fruit. The University of Arizona Cooperative Extension has a publication called “Growing Grapes in the Home Garden,” available to download at https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1657-2015.pdf. It features detailed information on training and pruning vines to achieve a bountiful harvest of table grapes. Grapes are a fun addition to any desert setting. Plant some this month, and soon your yard will boast eye-catching plants with bold foliage, sculptural branching and, best of all, colorful and tasty fruit that will be enjoyed by all members of the family.

Cathy Babcock is the director of horticulture for Boyce Thompson Arboretum, located in Superior.
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