The Kenwood Press|
Pruning - the beginning of a great glass of wine
The quality of a great glass of wine begins with pruning the vine. Pruning is the most important and most expensive job during the vineyard year. Every aspect is important. For example if you begin pruning too early, say early December, the vines come out too early in the season and there is excess danger from frost. If too late, say mid-March, grape maturity is delayed and you have greater threat from fall rains.
The secret - fifth grade math
Now for the parts of this math problem. We will use Zinfandel grapes as our example. Each leaf that grew last season produced at its base a new bud. We can get a good estimate of the number of leaves and hence the gross number of buds each vine produced last year. Each unpruned vine will have about 500 new buds. Each of these buds that grew in May and June of 2012 already has in it the cells for two bunches of grapes for 2013. Each prospective bunch will weigh about half a pound.
After 35 annual harvests here and knowing the terroir of this ranch - the soil, its depth, the climate, soil moisture and a host of other issues - we know that each of these Zinfandel vines can typically produce about 15 lbs. of mature fruit each fall. Now you can do the math. How many buds do you need to leave after pruning to produce the vine's quota of a total of 15 pounds of fruit? Answer: 30 buds, but keep reading.
It's not quite that simple
The vine determines how fruitful each bud will be; i.e., two big bunches, one tiny bunch, one tiny bunch plus one big bunch, or perhaps no bunches at all. The vine is worried about new vine propagation and the fertility of the seeds within the individual grape. All of these decisions are a function of the vine's total resources for both the current year plus anything good or bad from one or more previous years.
But the grower gets to play, too, by deciding how many extra buds to leave to account for these unknowns. At our ranch we usually leave 15 to 20 percent extra buds. In early summer if too many of these extra buds are fruitful, we may come in and cut off some of the young bunches to get back to our original vine yield plan of 15 lbs. of mature fruit per vine. Looking at these numbers you can see that in pruning our Zinfandel, we take off about 80 percent of the new buds, leaving the balance to yield the hoped for 15 lbs. of fruit per vine.
One more thing
Since the vines are not all equal in vigor, the pruner still has to make a few other decisions, remembering that the goal is for all the fruit to be mature at the same time. If the vine is a little weaker than its neighbors, the pruner will leave a few less buds. If the vine is a little stronger, he will leave a few extra buds. He is literally reading each vine.
To end with a new thought
We are still considering Bob Kunde's query so many years ago - “Are the vines happy?” Almost all vineyard work has been done as a function of labor costs and vine production. Could it be that there are some items that the vines would like to see and then reward us with better quality? How about the quality/cost/quantity relationships of different pruning and trellis systems? Are head-pruned vines happier? If, as reported, vines respond to wounds, what is the net effect of the number of pruning cuts/wounds on quality and - perish the thought - vine happiness??