Fruit grows only on wood that grew year beforeAs anxious gardeners wait impatiently for the snow to melt, they are dreaming of tasks to do while waiting for spring. Pruning is always a task that needs careful attention. Previous articles have talked about pruning fruit trees, and this week's column will focus on grapes. Grapes are an important part of any backyard orchard and allow you to produce fruit in a confined area with minimal space. Grapes are productive and are easy to grow under Utah conditions.
Carefully select the right kinds of grapes to grow here. Many different kinds are available, but Utah gardeners should select American or American hybrid grapes. European varieties require a long growing season and will not ripen consistently in our area. Prune varieties that grow here to a cane pruning system. Varieties grown in other areas of the country are pruned to different systems. Those are not discussed in this article. Specific grape varieties for this area will be covered next week.Proper pruning requires an understanding of three terms. These are the trunk, the fruiting cane and the renewal spur.
The trunk is the main stem of the plant. It grows from ground level to the top of the arbor or the top wire of the trellis. The trunk is a permanent part of the plant and the other parts of the plant are trained from it. Fruiting canes are created by cutting the long vines back to 10 to 15 buds. Long, healthy canes that are just larger than pencils produce the best fruit. Small, weak canes cannot produce good fruit, and large canes are all vegetative growth that will not produce fruit.
Renewal spurs are created by cutting long canes back to two to three buds. Remember that grapes only bear fruit on wood that grew the previous year. Grapes never come on wood in its first season of growth, nor are they borne on canes that are two years old or older.
Whenever you plant new grapes, it's important to start training them the year you plant them and each year after that. Vines usually start producing within three years after planting. Start training grapes the day you plant them. Get them off to a good start by cutting the dormant, bare-root plants back to two buds. Allow the bud to grow, and take the longest, most vigorous cane and train it to an upright position to become the main trunk. Do not worry about the side branches or canes the first year. By the second season, the plant produces the secondary branches. These will not produce fruit until the following year, but they should be trained to the desired permanent trellising system.
Many grapes are trained to a four-cane system. This means at approximately 30 inches off the ground, two canes are trained off from the main trunk going in both directions. Approximately 30 inches up from these canes, a second set of canes going in the same directions are trained. The fruiting canes formed during the second year will produce fruit the third summer.
Since they only produce one year, it becomes necessary to have additional canes to replace them the following year. This means renewal spurs must be created to solve this problem. Renewal spurs are created near the base of the fruiting canes to allow the production of long vigorous vines. These vines are not tied up or trained to the trellis during their first year, but are allowed to grow randomly.
After the canes bear fruit, they are removed the following spring. Remove the old cane near the trunk. Next, take the most vigorous cane that grew out of the renewal spur that you created the previous year. Tie it up to the wires and cut it back to 10-15 buds. Cut the remaining cane to two buds to create the renewal spurs for the next year.
The process is repeated year after year. After the canes have fruited, they are removed the following spring. The new vines are then tied up to the trellis and a new removal spur is created by cutting the canes back to two buds.
For maximum production with the plants in a vineyard situation, follow the guideline of leaving 10-15 buds per cane or 40-60 buds per plant. The major reason for pruning is to balance the fruit production that occurs on this year's wood with the wood production that will produce next year's fruit.
When vines are growing very vigorously, the natural tendency is to cut them back more severely to prevent them from growing as much. The opposite practice is best. Leave more vigorous vines with more buds so they can produce more fruit. This prevents the growth of excess wood and balances the fruit and wood production so each year enough fruit is produced to prevent excessive vine growth.
For additional information about pruning grapes, pick up a copy of the Grape Fact Sheet or the Pruning the Home Orchard sheet at your local Utah State University Extension Service Office.