University of Vermont Extension 
Department of Plant and Soil Science

Spring News Article


PRUNING GRAPE VINES


Dr. Leonard Perry, Extension Professor
University of Vermont
 
If you're growing grapes at home, late winter and early spring is the time for a major pruning.  Not pruning off enough is one of the biggest mistakes beginning grape growers make.  Between 70 and 90 percent of the previous growth should be removed this time of year, each year.  This is because grape vines, assuming you have ones hardy for your area, can be quite vigorous, producing more growth and fruit than roots can support.  Only prune less if vines aren't vigorous for whatever reason, such as poor soil, too little fertilizer, part shade, or poor match for your climate.
           
Grape pruning can get rather complex, and is for commercial growers, varying with region, training system, even cultivars (cultivated varieties).  But in home gardens grape pruning should be somewhat simple, especially after you do it a few times and get the hang of what to cut.  If you're too squeamish about cutting too much off, do some one day, then come back and do more the next, and so on until the vines have enough removed.
            
Don't worry about pruning just the right way, there really isn't one, and each vine is different.  Also these are vines not stone sculptures--if you do make a mistake, the plants will grow out of it.
           
The type of pruning will depend on what kind of structure or trellis you have to support the vines, and type of vines.  The most common home systems are either one wire strung between posts about 5 feet off the ground and parallel to it (the single wire system), or this and one wire half way between it and the ground (the two wire system).  These may have other names, depending on if the vines grow up to the wire, then are trained only in one direction (single cane) or with canes branching off along the wire in opposite directions (bilateral).
           
So a bilateral 2-wire system with 4 canes has one in each direction on the top and on the lower wires.  This is perhaps the most common home system, often called the 4-cane Kniffen system.  Since the older short stubs near the trunk, from which canes come each year are called "arms", this may be seen too as the 4-arm system.  The canes along the wires are called "cordons", so you may see this called the 4-cordon system.
           
If just setting up a trellis and planting grapes, put posts in the ground to a depth of 2 to 3 feet, every 8 feet along a row.  Posts should be 5 to 6 feet above ground.  You'll plant one vine centered between each pair of posts.  End posts should be angled outward (about 60 degrees from horizontal) so they don't sag inward.  Wires should have turnbuckles (as from hardware stores) on the ends, and on the wires leading to anchors on each end.  These keep wires taut.  On each end, use guy wires from the slanted (outward) posts to some form of anchor on or in the ground.  This can be a screw anchor as for trees or tents, or a buried block.
           
The second main factor to consider with pruning is the type of vine, which leads to the second type of pruning method.  In the above systems, canes are pruned back to near the trunk each year, leaving stubs (the arms) with only 4 or 5 buds on each.  This is called "cane" pruning.  If the canes are left on the wires and not pruned back, but rather the fruiting shoots from the past year that have grown off these canes are cut back, this is "spur pruning".  It's called this because when you cut back these fruiting shoots in late winter leaving only 2 or 3 buds on each, these short stubs on the canes are called "spurs."
       
Once you cut back all this previous fruiting wood, creating spurs, thin out the spurs.  There should be on every 6 inches or so along the cane along the wire.  This keeps too many fruiting shoots from forming the next year, more than the plant can support and still make good size clusters of grapes.
           
Cane pruning is used for most grapes. Spur pruning is mainly used on the vigorous southern muscadine grapes (where they're hardy in mild climates), as well as some European ones.  Spur pruning typically only utilizes one top wire.
           
Once your early spring pruning is done, there is one more time you'll need to prune.  Actually it is a thinning process once the grapes start forming in summer.  When fruit are rather small, only 1/8-inch or so across, remove whole clusters leaving only one or two bunches of grapes on each new shoot.  This is all the leaves on the plant can support in order to grow grapes with the size and flavor to which we're accustomed.  You should remove any clusters that start forming the first two years after planting so the plant can direct all its energy into growth.

   

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