Posted: 09/04/2013 at 00:26
Peter, I'd be tempted to give it a little water if the top couple of inches in the pot is dry. I grow a huge one outdoors (it's at least 40 years old and 50-60ft long) and it is as tough as old boots. Whatever you do though, do not prune it now or it will bleed, possibly to death. If you are growing it along the length og the GH, train it using the 'rod and spur' system and once you see the fruit forming in a few months, count 2 or 3 leaves from the bunch towards the growing tip of the shoot (spur) and nip it off there. Those 2/3 leaves will be ample to feed the developing grapes, but if you let the shoots keep growing (and, boy, do they grow fast!), the vine will waste its energy in them instead of putting it into the fruit. Don't let more than one bunch of grapes form per spur. Growing as a standard is slightly different (see RHS link below.)
As it's in a pot, once it starts growing, water very regularly and feed occasionally with something like tomato feed.
Ideally, you would plant the vine permantly just outside the GH and train it inside through a small opening, or plant it in the GH border. See the comprehensive RHS advice for glasshouse grape cultivation: