Ask Mr. Smarty Plants

Of course it is feasible to train grape vines from your oak tree 15 feet to a nearby arbor, but there may be grape fruit yield consequences. Larry Stein and George Ray McEachern of the Texas Cooperative Extension have written an informative article about Table Grapes: A Potential Alternative Crop that addresses pruning and canopy-to-yield ratios. If the canopy is too large, the crop will be small. Take a look at the information on the Texas Winegrape site for more details about how to train your grape vine as well as diseases and growing table and wine grapes.

Here's what they say about pruning...

Proper pruning results in vines with good vigor, large clusters and large berries. If the vines are too vegetative, the crop will be short and fruit quality will be low due to shading year after year. On the other hand, if over-cropping is allowed to occur, the fruit will be low quality, harvest will be late, and in extreme cases, the vine can die. Unfortunately, there is no simple rule for pruning table grapes; each vine needs to be pruned to maintain the delicate balance between vine vigor and fruit production. This is not easy and is often misunderstood even by professional horticulturists and commercial grape growers. Factors to consider in controlling vine vigor include: climate, soil, variety, rootstock, irrigation, weed control, trellis, cluster thinning and other forms of management.

Sunlight is also a major consideration for the table grape grower because it controls fruit quality and fruit bud initiation for next year's crop. Light must contact the developing buds in the leaf axils on the lower end of a shoot during May and June each year. This sunlight is essential for the initiation of fruit buds for next year's crop. If lower buds on this year's shoot are shaded by more than three leaf layers, next year's crop will be low with fewer clusters and fewer berries in each cluster. Therefore, the grape grower needs to manage vine vigor so that sunlight can adequately reach developing buds. Fruit thinning by hand is necessary to produce large cluster and berries.

Optimum vigor shoots will be 3/8 to 1/2 inch in diameter and contain 15 to 22 healthy leaves in July when the fruit are developing and ripening. Every vine must be managed by pruning to the correct number of buds so that the shoots will have the vigor and sunlight. Vines which make excess growth one year will need to be pruned to leave more buds the following year. Vines which are weak need to be pruned harder, leaving fewer buds to increase vigor. Each vine should be evaluated every year to determine the proper number of buds to leave on the vine after pruning.

The Cane Count rule can be used to estimate the proper number of buds to leave after pruning. Using the Cane Count rule, if a vine produces 40 healthy canes measuring 3/8 inch in diameter, leave a bud for every cane minus 10 percent, leaving a total of 36 buds on the vine after pruning. Using this rule, the table grape grower can determine the exact number of buds to leave on the vine after pruning. If pruning is ignored, and the vine is allowed to grow unmanaged, excess vigor, poor quality, over-cropping, late harvest, and potential vine death will result.