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Question: Any suggestions on a good variety of table grapes to plant in my back yard?  — Dennis V., Rio Rancho, NM

Answer: With more than 10,000 varieties of grapes in the world, you’re right to seek help when picking the best one for your garden. We sent your question to our NMSU Extension Viticulture Specialist, Dr. Gill Giese. Here’s what he has to say:

Grapes are the most common deciduous fruit crop grown worldwide, and table grapes are popular and common in New Mexico home gardens. However, it is important to select varieties adapted to your local climatic conditions. The most significant climatic obstacle to successful grape production is low or extreme cold temperatures. 

Winter hardiness, the ability to survive low temperatures during dormancy, differs among major grape groups. Varieties derived from Vitis vinifera (European grapes) that originated near the Caspian Sea are the least winter-hardy. These varieties are adapted to a warm, dry growing season with more than 180 frost-free days and mild winters.

The eating quality, specifically their non-slip skin, crunchy texture, seedlessness, and relatively high sugar content, contribute to the popularity of these varieties. They can thrive in southern New Mexico, but unless a protected site is available, they are not recommended for northern New Mexico. 

Varieties of North American origin, Vitis labrusca, are much more cold-hardy and require a much shorter growing season: 140 to about 170 frost-free days. However, these varieties are subject to iron chlorosis (leaf yellowing) due to high pH or alkaline soils and are generally considered of lower eating quality. A variety is seldom described as having “poor” or “undesirable” eating quality. The key word is “quality.” Beyond measurement of sugar and acid content, “quality” is a subjective judgement, difficult to translate into a meaningful recommendation.

A third group, hybrids between the European and American types, are intermediate in winter hardiness, require a growing season of approximately 160 frost-free days, and are generally not susceptible to iron chlorosis.  

Varieties listed below are thriving in different parts of New Mexico, and some were planted years ago at the NMSU Agricultural Science Center at Los Lunas:

Vitis vinifera types (for southern New Mexico): 

• ‘Thompson Seedless’

• ‘Fresno Seedless’

• ‘Autumn King’, a recent release with berries as large as 10 grams each 

Hybrid and Vitis labrusca types:

• ‘Himrod’, a cold-hardy, early, white, seedless variety with good eating quality. This variety has ‘Thompson Seedless’ (the ubiquitous white/green grape available at grocery stores) as one of its parents. The rachis of this variety can become brittle, and fruit can “shatter” or “shell” (i.e., fall away from the stem). This hybrid is productive and widely planted. Released from Cornell University in 1952.

• ‘Glenora’, a blue-colored, seeded grape that many New Mexico growers report as their most productive variety. It is thriving at the Heritage Farm demonstration vineyard within the Albuquerque Botanical Garden.

• ‘Reliance’, a pink-red grape that can develop high sugar and labrusca flavor and is very cold-hardy.

• ‘Mars’, a tough, blue, slip-skin type with vigorous vines; requires cluster thinning; has labrusca-like flavor.

• ‘Jupiter’, an early maturing, tough, slip-skin variety with red-blue color; has a muscat-like flavor.

• ‘Vanessa’, a variety developed in Canada, is likely the most cold-hardy of seedless types; fruit quality is highest among red seedless hybrid types, but can develop noticeable seed traces.

• ‘Concord’, a Vitis labrusca, blue, slip-skin variety with traditional “grapey” flavor, with prominent seeds.

• ‘Steuben’, a Concord-like variety, but with better flavor described as “sweet and spicy”; easy to grow and requires cluster thinning; seeded.

• Recently released non-slip skin, mostly seedless table grape varieties to try: ‘Faith’ (blue, semi-crisp flesh), ‘Gratitude’ (green, crisp flesh), ‘Hope’ (green, soft fruit texture), and ‘Joy’ (blue, but very soft texture).

Beyond variety selection, there are some techniques table grape growers can use to increase or maximize individual grape berry size: pruning, cluster thinning, berry thinning, girdling, and gibberellin application. Find more information in NMSU Extension Guide H-311, “Improving Size and Quality of Seedless Grapes,” at http://aces.nmsu.edu/pubs/_h/H311.pdf.

Grapevines tend to produce more clusters than the vine can support to full maturity; thus, pruning will fit the vine to your trellis system and control crop load. After fruit set (you will notice that flower parts have fallen), remove clusters that are small or misshapen or touching adjacent clusters. Applying the plant hormone gibberellic acid is a common commercial practice to increase fruit size. 

Girdling is a practice in which cambial tissue, specifically the phloem, is physically cut away and removed from a cordon or cane just at berry set. With the phloem cut off, the photosynthetically derived sugars produced by leaves are directed to the clusters attached to the girdled cane. Often, bigger and sweeter grape berries are the result. [Please note: Girdling in grape cultivation is different from tree girdling. Check back next week for distinctions between the two!]

Visit www.NMSUdesertblooms.blogspot.com for links to many more helpful resources on grape growing in New Mexico, both for the table and the glass!

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/. 

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.

‘Faith’ table grape at the NMSU Agricultural Science Center in Los Lunas, about 10 days post bud break. Nascent flower clusters are barely visible in center of the young shoot in lower portion of photo (photo credit G. Giese).

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