Spring cluster thinning

Hmmm, not the vinifera expert, but I will wade in as this is sorta OT for a wine group, not grape growers.

First off, it is unusual to spur train vinifera they do much better with canes and VSP. American and hybrid vines are more productive on the basal buds than vinifera and the technique is easy so that's what many people use (spurs vs. canes).

Depending upon how many shoots were produced last year, you are probably way over cropped. Assuming you have twin cordons, each cordon should have a max of 10 spurs each. Figuring out how many each plant should have requires the prunings be saved and weighed, first pound of prunings is used as the base (30 buds) and each additional pound will gain another 10 buds to be left. As you may or may not know, it takes quite a few trimmings to make a pound of canes.

Cluster thinning is a good thing. Shoot thinning at the proper time is also good, but remember this is the way that the plant stores up its reserves. Too much thinning will weaken the plant and limit the load of grapes it can bear and ripen (two different things). Combing of the shoots is prefered until verasion of the grape and then leaf thinning to increase exposure to sunlight to maximize ripening.

Water in the spring won't hurt you, but it would right before or during harvest. I'm organic as I can be (in Kentucky sprays are required, sigh...) so I can't advise on fertilizer, I use compost and ducks in the vineyard. Most peoples recommended side dressings of commercial 12-12-12.

Finally, 2 clusters per shoot should be the max.

go to the uc davis site and find out all about grapes in good ole' caliphoney (i'm a 3rd generation californian living in the south)

Terroir is off topic here?

Thanks for the quick reply. I do use this newsgroup a lot for winemaking. I tried this question in another spot that is only for grape growing, and got no replies, so I gave this a shot, since I know there are a lot of growers here as well.

I just re-read one of my books, which is only about vinifera, and it does say to prune to two buds per spur. So let's say I have twin cordons, and I have 10 spurs on each. Each spur is pruned to two buds. (I always thought the reason to leave two buds is just in case one doesn't grow in the spring). So if you end up with shoots out of both buds, and each shoot has cluster(s), is that too much? Every picture I have of cluster thinning shows just a single shoot and indicates that you should thin down to 1-2 clusters per shoot. But if there are two shoots on each spur, isn't that too many clusters per spur? With the idea of 10 spurs per cordon and one cluster per shoot, it would be a difference between 10 clusters or 20 clusters on that cordon.

This is the part that always gives me a headache!

I'll check out the UC Davis site as well, good idea. Thanks again,

Linda

Linda - I'm in the Kansas City area and I grow some vinifera as well as hybrids. I would approach your pruning with a pounds of grapes per vine point of view. My Cab Franc clusters weigh about 1/3 pound each. I'm not interested in maximizing crop yield. I want to be sure the vines can ripen their crop so I'm limiting the crop load to about 6 - 8 pounds per vine. I'll leave about 18 to 24 grape clusters per vine after I'm sure all cold weather and hail threats are over (I guess you don't have these problems). You can go crazy counting grape clusters but with 15 vines it shouldn't be a big deal. See if you can find out what crop loads locals target for with your grape varieties. The county Extension agent might have some information. Vintage Nursery or Nova Vine may have good information. Also, Ernie Bowman over at Kendall Jackson Nursery is very helpful with grape vine questions.

Bill Frazier Olathe, Kansas USA

Depending on whether it is too many or not is a subject of debate and can lead to holy wars on the topic. Dr. Richard Smart says one way to control vigor is to hang more fruit. Excessive thinning MAY result in more excessive vigor and MAY not any increase the wine quality. I would, however limit each shoot to no more than two clusters. How far apart are your vines? If you have room between vines, you could extend the length of your cordons next year and this may reduce vigor. I think you should taste the finished product and determine the proper crop load for your particular location. This year you could also do what is called green harvesting - after verasion has commenced and the clusters are predominately colored, find the clusters that still have a high percentage of green berries and drop them. This will even out the ripening of the remaining fruit and you will not have immature fruit when you harvest the rest of your crop.

Linda,

"it seems like it formed a second bud and I have two shoots kind of going in a V shape from the cordon. "

You didn't count the "basal" bud or the bud right at the intersection of the spur and the cordon. BTW, there is nothing wrong with you choice of pruning. There are a lot of growers in california who low cordon prune their vines on a VSP trellis. It actually is a good system.

" It seems way too vigorous to me." You want the vines to look healthy. I'm not sure how you can tell if the vine is too vigourous so soon. Are the distances between nodes on the canes longer than 6 inches???? If not the vine is probably not too vigourous. Don't sweat the water. VINES NEED WATER. Only nearing harvest is when you might worry. Let them grow. They know what to do best. As far as crop load if last year was your first year I'd suggest keeping ~20 clusters per vine. I wouldn't call your viners "mature" yet. Start from there and see how it goes

Bob

Thanks to all of you for your replies and help! You've given me a lot to work with.

Linda

Dear Linda,

I have Syrah and Grenache vines, we prune by the spur method to two buds (eyes), each develops a shoot which we keep. We go through our Syrah vines and remove any additional shoots by hand, the Syrah vines are trained on a 3 wire system and the Grenache on a single wire or bush (goblet). The vines only have a total of six spurs each. I am situated in the southern Rhone our climate may be slightly cooler than yours and the density of plantation must differ. Our vines are not irrigated; it has hardly rained here for six months. We have just started the process of removing shoots that we consider unnecessary, known as ebourgeonnage here.

Hoping that the above, may have been of some interest to you.

Arthur