Grape pruning

[Eoghan]

Having pruned ruthlessly when it was dormant, there are over 40 grape clusters developing.
1. Do I need to thin them out, given that they are spread over 20' or so of the polytunnel
2. Should I prune the shoot that has the grape cluster on it? The one pictured below has a nice cluster developing but it is also growing a new shoot, which I am tempted to terminate.

If I prune the shoots with clusters that would appear to be a second pruning. The first encourages grape development, the second stops growth going into leaves rather than the fruit.

[ameno]

You should thin to one bunch on each new shoot. Any more than that shouldn't really be necessary.
Traditionally, you would then prune all fruiting shoots to 2 leaves beyond the bunch, and all non-fruiting shoots to 2 leaves. Any further side shoots which develop should be pruned to one leaf.
However, as far north as you are you may want to go easy on the pruning. The grape needs those leaves in order to develop enough sugar to ripen the fruit, and the sun isn't nearly as bright up where you are.
That being the case, I think I would just recommend pruning only the shoots which are in the way or getting tangled with each other. Then, a bit late in the summer (early August, maybe), as the fruits just begin to ripen, remove any leaves which shade the fruit.

Either way, with summer pruning you only prune the new growth. Don't touch any brown wood. That's a winter job.

[Eoghan]

Either way, with summer pruning you only prune the new growth. Don't touch any brown wood. That's a winter job.

This is what I am coming to - two prunings per year, a dormant pruning to promote fruit and a summer pruning to encourage energy going into the fruit.

[ameno]

This is what I am coming to - two prunings per year, a dormant pruning to promote fruit and a summer pruning to encourage energy going into the fruit.

Indeed. And winter pruning should be hard. Once the vine is three or four years old and the basic framework is established you want to remove 90% plus of that year's growth each winter. With mine, I cut all of that year's growth back to one or two buds. That way, the basic framework grows only a tiny bit bigger each year.

[Eoghan]

Wow 90%! Started pruning the fruiting shoots today. Some of the shoots have two clusters and one is obviously the runt. However some shoots have two decent clusters forming do you go with the first or second? If you go with the second will the earlier leaves contribute to it? I suspect there is a rule of thumb, I just don't know it.

I am fearful of removing leading shoots from non-fruiting shoots to take them back to two leaves. What about rooting the cuttings?

[ameno]

Yeah, 90%+. You need to prune grapes very hard or they very quickly end up as massive uncontrollable and unfruitful triffids.

If a shoot has two similar sized bunches of flowers then I don't think it matters too much which you remove. Although the lowest bunch is likely to open sooner, and therefore (all else being equal) ripen sooner, so that may be a factor worth considering (although its likely only to be a matter of days, a week at most). How many leaves are where on the plant doesn't matter. It's all one system, so all that matters is total leaf cover.

Grapes do need a certain amount of leaf canopy in order to produce enough sugars to properly ripen the fruits, so since you might not get as much sun where you are, you may want to consider not shortening them quite as much as one normally would. But you don't have to worry in terms of the health of the vine or any impact on next year's flowering. Vines fruit on the current year's growth, so an established vine will always flower, no matter how hard you prune it.
As for cuttings, I wouldn't bother. Softwood cuttings from grapes can be rooted, but hardwood cuttings (taken November-January) root much more easily and grow more quickly into mature plants, so if you want more grape vines I would just take hardwood cuttings in the winter.

[Eoghan]

The grape appears to be self-fertile and does not appear to "flower"?

Just looked online and the "furr" is the flowering????

[Snoop Puss]

It might be self-pollinating, but you won't get fruit without flowers. No idea what 'furr' is, but have a look at this picture of grape blossom:
https://commons.wikimedia.org/wiki/F...pe_Blossom.png

[ameno]

The grape appears to be self-fertile and does not appear to "flower"?

Just looked online and the "furr" is the flowering????

Grape flowers are insignificant. They have no petals and are very small. You'll know they are open when you can see the anthers (the tiny bits which hold the pollen). This is probably the "fur" you are talking about.

Grape flowers are self-fertile, but that doesn't mean they are self-pollinating. They still need insect pollination. The only ones which do not are the seedless varieties, as they set fruit without any pollination (which is why they are seedless).

[Eoghan]