When vines shed their leaves ,they go dormant. This happens as the temp-
riture goes down.The dormant season ends as soon as the temperature
starts going up.It is THEN the time to prune vines. Pruning is an essencial
yearly job, to establish a well shaped vine and to make this tree productive. The first two or three years should be dedicated for shaping. All side shoots should be discarded and leave a main stem to grow to a desired height. Side shoots would be then allowed to stay and to become branches. Each year these branches should be reduced in mumber,and those that stay will be cut back to leave about five or six nodes.As was said earlier, this job is done yearly while dormant and before sprouting time.

Pruning must be done during complete dormancy such as mid winter well before the sap starts rising in spring or the plant will simply pump all the sugars it has stored in it's roots over winter straight out of the newly opened cut ends. By pruning in the dead of winter, the cut ends will dry out and die back a few millimetres effectively forming a plug.

We always prune them the first week of January, here, and that should work in the UK, too--as long as you bundle up well! Some kinds of grapes won't produce unless you leave a foot long stem from last years growth about every foot and a half, or so (called "cane" pruning) since the buds at the base of the stems don't produce flowers. Some of the hardier kinds of grapes are notorious for this. Other kinds fruit best when all of last year's growth is cut back to two buds ("spur" pruning)

We planted a grape vine in 2007 and it hadn't produced any fruit until this year.