In yesterday’s post, I mentioned that my Pinot Noir clone, ESP374, is not highly regarded. Its biggest problem is that it sets more fruit than it can ripen well. It over-promises and under-delivers, and, ever the optimist, does the same thing year after year. To make good wine from this clone, I pluck out immature grape clusters until there are no more than the vine can ripen. It’s called cluster thinning, and most vines can benefit from it. But how do you know what the right number of clusters is?

There’s the expensive way: you can hire someone else to tell you. There’s the cheap way: you can ask another grower in your area. There are also rules of thumb published in books and on the internet. All of these answers will be for vines, planted in conventional vineyards, that are free to grow their roots as far down as they like. In fact, the answers will usually be in terms of tons/acre (or tonnes/hectare). What about all of us suburbanites growing grape vines in pots? We trim the roots and are left with vines that can produce less than if they were planted in the ground. So even if we could convert tons/acre into pounds/pot, we would still be over cropping. It looks like we’re on our own.

I can’t explain this glaring and puzzling oversight, but here’s how I deal with it. I control the hight of the vine for my convenience; I need to be able to reach the top easily for pruning, harvesting, applying bird netting, and so forth. I look for opportunities to create a spur, and prune each spur so that it’s long enough to push at least one fruitful bud. I suppose I’m relying on the vine to push the right amount of foliage for it’s root system, and managing the buds and clusters so that all the grapes ripen well. I thin to insure that there is only one cluster and at least fourteen leaves per shoot. If I find that some shoots don’t push out enough leaves, I’ll aim for two shoots per cluster next season. To do that I would thin one shoot normally, then remove all clusters from a neighboring shoot. The goal is to make sure that there are enough sugar-producing leaves to ripen all the grapes.

I’m making some changes for my Swenson Red, as I mentioned in this post. As I learn more, my approach will evolve.

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