Pruning Grapevines 101
A common conversation in our tasting room starts with, “Why do your grapevines look different than the vines in some other vineyards I have visited?” Or, “How do I prune the grapevine in my yard?!” These are great questions, and we are always happy to explain.
At Six Sigma Ranch, we start pruning in February. We prune to maintain the shape and size of the vine, and to control the ratio of canopy (leaves) to fruit. Most of our vines use spur pruning (also called cordone pruning), which means we cut them to the shape of a “T” every winter, with 4 to 6 spurs (small wooden knobs) on each arm of the “T”. We tie each arm on a simple horizontal wire, and use two additional horizontal wires to contain the canes (new shoots) as they grow up.
Two facts impact our pruning decisions:
1. A grapevine sets buds in the fall. These buds push new shoots in the spring.
2. Under a given set of circumstances, a grapevine will put out a certain total shoot length, regardless of how many buds it has. That is, if you leave a total of 4 spurs with 2 buds on each spur, you get 8 shoots that grow, let’s say, to a length of 4 feet each (32 total feet). If on that same grapevine, you leave twice as many (16) shoots, each of the shoots will be half as long (2 feet).
Our goal at harvest in most cases is to have 3 ft shoots, each supporting one or two clusters of grapes per shoot. We find that this ratio of canopy to fruit lets the vine build sugars at a rate that matches grape maturity with sugar ripeness, or, in other words, makes great wine.
But how does the thing begin? When we plant a new vine, we let it grow untamed for the first year. The second year, we prune it back to two buds. The third year, we take the strongest of the two new shoots and let it become our trunk, the “I” in the future T-shape. (During those first three years, we remove all grape clusters to leave all energy for vine development.)
After the third season, we leave two buds at the top of our thin trunk. Each bud becomes a shoot that becomes an arm in the permanent T-shape of the vine. We then let the vine grow shoots from each of the buds on the arms. These shoots are pruned the following winter so we end up with, say, 4-6 spurs on each arm, each spur with one or two buds. This procedure is repeated every year in the lifetime of the grapevine.
If you are starting with an un-managed vine, you can use the principles above to still gain control. Simply trim the thing back to a single trunk and tie that trunk to a stake. Select some arms (3 or more) off the top of that trunk and use the shoot-length formula to estimate how many buds you want to keep on those arms. You will be fighting unwanted shoots the first few years, but simply brush them off while they are small and carry on. The result, a vine that looks like a small tree with some arms, is called head pruning. It is common in old-world wine regions like Spain.
There are other ways to prune grapevines including cane pruning, but the basics above will let you grow great grapes and impress your friends for years to come!