Any thoughts on this ^^, or should I just stop fiddling with it and see what happens?
Just so you’re not confused by my wording later in this post, standard grape vocabulary in my part of the world uses laterals to refer only to the shoots that grow out of the leaf axils of the current year’s growth. What you’re calling laterals are just shoots. Or primary or fruiting shoots if you want.
To ripen fruit, you need at least 14-15 well-exposed leaves on the shoot. You get some compensation from neighboring shoots if they don’t have their own fruit, but I would not take too much growth for cuttings if you want fruit this year. The shoots you topped will send out laterals and keep growing eventually, but it may reduce fruitset.
On the plus side, topping the shoots on the upper cane will promote growth on the lower cane.
That is a good idea. I’ve read that it was pretty common to do this with greenhouse grapes in northern Europe.
I would not do a vertical cordon, nor try to keep the shoots growing off the cordon horizontal. The growth of the lower shoots will be severely inhibited by the upper shoots.
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Thanks. I was looking at this diagram in a book by Dr DG Hessayon, a UK botanist who’s written a huge number of succinct books on gardening.
I think his leader is your cane, his laterals are your summer shoots, his sub-laterals are your laterals?
It looks like I should leave well alone for now, and maybe post an update in Nov-Dec for advice on pruning, and maybe, flexibility allowing, poking that upper cane into the greenhouse.
The only thing in the meantime would be when I take cuttings - I only need one or two to plant in the polytunnel.