By J. King, WSU – Mount Vernon
Standing in front of a mass of tangled grape vine and wondering what to do with it can be a scary experience for the novice or even for the more experienced pruner. Keep in mind two essential ideas:
--Don’t be afraid to cut.When you finish, about 90% of last year’s growth will be cut.
--Grape plants are vigorous, and forgiving. Even if you make a mistake, you’ll get a chance to fix it next year.
With that said, you can approach your pruning in a spirit of learning and adventure, not panic. Grapes are best pruned in spring (February/March, or even as late as early April) because if pruned too early a hard frost in late winter can damage the canes and buds.
Grapes bear fruit on the green shoots that arise from one-year-old canes. Pruning is based on producing fruit in the current season, and renewing young canes for the next year. The old canes that produced fruit this season will not produce again. There are several methods used in pruning established grapevines. Cane pruning is the usual system in climates like ours where heat units may not be high and vigorous vines can shade the fruit.
In this system a permanent trunk is established, and every year new canes are selected from the head of the vine, where trunk and wire intersect. One or two canes on either side, each 8-10 buds long, are selected and tied to a horizontal supporting wire, and all other canes cut out. Choose canes that are about the thickness of your little finger, that come out as close to the head as possible, and that have buds fairly close together. Try to avoid large thick canes with buds spaced far apart. Also leave one or two spur canes, cut to two buds each. They will provide additional canes to select from for the next year's pruning.
Some helpful hints:
--Take time to look over the vine before you start
--Pick out several well-placed canes that look like good prospects.
--Cut out old wood and canes that are obviously unsuitable – canes that are small and weak, or too far out from the main trunk. This will clear up some of the confusion as you go.
--Always leave at least one alternative cane until the last, in case you break one.
--Bend canes gradually into place before tying. Canes that grow in a direction other than where you want them can often be persuaded to cooperate by cracking them gently. Use both hands to bend the cane at the point where you want it to change direction, and apply pressure just until you hear the fibers crack.
Each grape shoot needs 14 to 16 well exposed leaves to properly ripen a grape cluster. If too many shoots are crowded together, the leaves do not get enough light for effective photosynthesis. It is important that all the leaves get good sun exposure, because shaded leaves only function at about 6% of their capacity, and may not be contributing at all to ripening the grape cluster. Thinning grape shoots in the early stages eliminates shoots that are unproductive and provides light and space for the productive ones. Helpful hints:
--Begin thinning shoots as early as possible -in June or as soon as clusters can be seen.
--Shoots are soft and can easily be removed by hand. Space the shoots 3” to 4” apart.
--If there is more than one fruit cluster per shoot, the lowest one (closest to the old cane) will usually ripen earliest.
--Unless clusters are very small it’s usually best to thin down to 1 cluster per shoot, especially if there are 3 or 4 clusters.