Posted: 30/05/2013 at 18:47
What size pot is it in and how old is it? I guess that it is Sauvignon Blanc, a white grape rather than Cabernet Sauvignon which is red. Not the easiest grape to try in the UK as it is a late ripening variety and will need that sunny sheltered position.
Grapes grow in very poor soil which isn't much good for anything else so don't be tempted to feed it often. You will only create a monster as it will respond by producing lots of lush growth, up to 5 metres a year.
You can expect grapes in the third or fourth year but should limit the number of bunches in the early years, only one or two per plant in the first fruiting year. Get it trained early to get the best out of it. If the trellis is wide enough (2 metres minimum) try the double Guyot system. Sounds complicated but basically you have 3 shoots produced each year which you train the following year. Two shoots go horizontally left and right and one goes straight up. The horizontal shoots produce vertical side shoots and this is where the fruit comes from. Grapes fruit on new wood. The vertical main shoot is used to produce three side shoots which become next year's horizontal and vertical shoots and replace this year's.
You might also have to thin the bunches to get decent grapes, remove about half of the grapes in a bunch when they are about pea sized. This gives you bigger grapes, less congestion and less disease.
Treat the pot every year for vine weevil, use nematodes not chemicals.