University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article


NORTHERN GRAPE GROWING

Dr. Leonard Perry, Extension Professor
University of Vermont
 
Growing grapes in cold, northern climates isn't difficult if you've chosen hardy varieties, a good site, and follow some cultural basics.  This includes knowing the basics of pruning grape vines.
           
There are three basic groups of grape varieties.  European or vinifera varieties include such popular names as Cabernet and Riesling, and aren't hardy below about -10 degrees F (USDA zone 6).  American or labrusca varieties such as Concord and Catawba are hardy to -15F or colder.  Some of the most hardy, developed in Minnesota and often known as Swenson varieties after their breeder, include names such as Frontenac and Prairie Star.  Hybrids of the American and European varieties have moderate hardiness from -10 to -15F. 
           
The best site is one with full sun, good air drainage, and soil that isn't too wet or dry.  Grapes do tolerate a range of soil types and soil drainage.  Avoid north-facing slopes and low areas that remain cooler and delay fruit ripening.  Choosing a warm microclimate, such as near a building or a south-facing slope, you may be able to grow varieties not listed for your hardiness zone.
           
Once a site is chosen, erect a trellis or arbor.  A split rail fence works well too, and is attractive.  Grapes grow on most any structure, including trees.  They can cover evergreen trees in a few seasons, killing branches.  The goal is to use pruning and training to keep grape vines manageable and productive. A common trellis system is known as the "four-arm Kniffen system", and consists of two wires at three and six feet high, strung tightly between wooden posts 24 feet apart.  Training comments refer to this system, but the principles apply to others.
           
Whatever system and structure you use for training, keep in mind three main principles:
--Vines should have only one or two layers of leaves during a season.
--You should prune up to 90 percent of new growth off during the dormant season in late winter or early spring.
--Vines will bear fruit on current-season shoots that grew from buds on side branches from previous year growth.
           
Plants roots in spring, as soon as the soil can be worked, spacing plants eight feet apart.  Make holes large enough for the roots, trimming excessively long ones.  Water well. Don't fertilizer the first year.  In subsequent years use two ounces per vine of 10-10-10 or the equivalent in year two, increasing to 16 ounces per vine in year five and after.
           
Remove all but the best single cane, and tie it to the trellis bottom wire or a stake.  They need support to grow straight.    Buds will grow in a few weeks.  As the single cane grows, remove all but the strongest shoots, and flower clusters as well.  Your goal is to have one single cane reach the top wire of a trellis the first year, or if not then the following spring. 
           
Early in the second year, tie the cane to the top trellis wire, and cut it off just above the wire.  Leave four to six buds near each wire, then remove any others as well as any flower clusters.  Allow these buds to grow into shoots the second year.
           
Early in the third year, while vines are still dormant, prune them hard.  Select four healthy canes or side shoots near each wire to keep, then remove the rest.  Train one cane on each wire going in each direction, so two on the lower wire, two on the upper.  These are the four "arms" of the Kniffen system.  Allow these four arms to fruit up to the sixth bud along the stems.  Cut the remaining four canes back to a couple buds.  These are the "renewal spurs" that will produce fruiting canes next season.
           
In subsequent years, remove the fruiting canes from the previous year.  As the shoots grow from the renewal spurs, train two to each wire, then prune after it has produced ten buds.  You should have two shoots left on each wire, which you can prune back to two buds for next year's renewal spurs.  The whole point in this pruning is to have enough buds for shoots to produce fruit, but not too many which will result in poor quality and vine growth.
           
Often the most productive buds, then shoots, are at the top of the trellis where the previous season buds were exposed to the most light.  Ideally the distance between leaves should be about six inches, with the cane diameter between leaves one-quarter inch or more.
           
For arbors, prune annually, but allow the trunk to grow longer, and keep more fruiting canes and spurs.  Train short, permanent arms from the main trunks so leaves will cover the arbor.
           
Harvest grapes when fully ripe, since their sugar content does not increase once they are picked.  The peak is usually about one week after grapes have good size and color.  After this the quality goes down rapidly.  Yields will vary with season, site, vine vigor, and culture, but by the third year might be five to ten pounds of fruit per vine.  Remove bad grapes from clusters before storing the good ones in refrigeration.
           
Controlling weeds is essential for best fruit quality and yields.  This is best done with frequent, shallow cultivation around vines.  Organic mulches, such as bark or rotted sawdust, will help control weeds and conserve moisture.  These mulches may keep soils cooler, delaying ripening.  Also they may harbor rodents in winter that can damage vines.            
           
Good air circulation, pruning infected shoots, and using less susceptible cultivars are non-chemical solutions for diseases.  Diseases to get familiar with, and watch for, include powdery mildew, black rot, downy mildew, and botrytis.  Insects to learn about and watch for include Japanese beetles, grape berry moth, grape cane girdler, and grape leafhoppers.  Birds and raccoons can be problems with grapes, especially the larger seedless varieties.
           
Learn more on potential grape insect pests and diseases in Cornell leaflets online (nysipm.cornell.edu/factsheets/grapes).
            

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