As I write this at dawn, the sky is clear and the view across the Sonoma Valley is beautiful. At first light it is a green world. During February we finished our annual pruning and have tied all the pruned canes securely to the trellis wires. At this time of year, tying the canes seems like a waste of time, but by midsummer each cane will, we hope, be carrying small grape bunches that will weigh about a third of a pound each when mature, plus the weight of the new growing canes and their foliage. The weight of all this could easily break the fruit-bearing canes.
Over the years we have received numerous questions from homeowners about how to prune their few backyard grapevines. The key is the number of buds you leave on each vine. In late summer, if you look carefully at one of the mature canes with some 20 leaves, you will see at the base of each leaf a small brown bud about an eighth of an inch long. Pay attention. This small bud is your crop for next year. Each of these small buds has an agreement with me: “Patron, if you leave me and do not prune me off this winter, we have a deal. I promise you that next September I will deliver to you two bunches of grapes with enough sugar and flavors that you will be able to obtain some great wine or just plain grape juice.”
But you need a little more information. Each of your vines will typically produce some 30 pounds of mature fruit. Each mature bunch normally weighs about a quarter of a pound. Now you can solve this yourself. After winter pruning you want to have left just enough buds, at two potential bunches each, that will in turn yield about 30 pounds of fruit per vine. The vine can get this amount of fruit mature and with good favors.
As a beginning grower you will usually leave too many buds after pruning. Typically after pruning you want to have left some 30 to 40 buds per vine. This, in effect, means that you will have pruned off a huge percentage of the new buds that grew last summer. If you leave too many buds, the crop will be too heavy for the vine to mature it properly. Often in mid-summer you will have to go out to your vines and actually count the number of bunches.
If, instead, you leave too few buds, the remaining fruit will be light and the crop will ripen ahead of normal harvest time. It may take several harvests before you can match the vine’s fruit load with its strength. But remember, if you leave too many buds you will have to come out midseason and cut off some of the fruit, remembering that a typical vine in this area can only get some 20 to 30 pounds properly mature, either for eating or for winemaking. Some time in mid-July, be prepared to go out and count the number of small bunches on two or three vines. In vineyards planted in rich, deep soil you can ripen a bigger crop. But at our ranch we are often around 20 pounds per vine in a normal year.
It is almost the first of March and we have had more than our share of nice warm days. This is a worry, because if we have early bud break and the new canes begin to grow, they will be vulnerable to a severe late frost. We know that this is a possibility, because when we prune a small cane, within a few minutes the raw cut begins to bleed with large amounts of sap from the newly opened cut. When the vines are fully dormant this does not happen. But a piece of news re: global warming. Our foreman tells us that it has been three years now since we have had a severe spring frost.