I am a resident of Hampton Wick, a village in the south-west corner of London U.K.
I have lived at my present home for more than thirty years. My late mother brought a couple of grapevines from the house where she had previously lived for sixty years.
I don't know the age of these vines are, but they are old and, I regret to say, neglected by me.
The photo above shows the productive vine competing with ivy, to climb an old pear tree.
the layout of the garden
The garden runs east to west, with a large Victorian house at the east end. The vines are on each side of the garden. You might expect the vine on the south-facing wall to be the best but no - the garden is badly shaded by tall trees. At the moment, that vine produces no fruit.
This year, 2011, has seen the vine on the north-facing wall produce more than two dozen various-sized bunches of grapes. Now it has been a good year for fruit, yet several local vines have produced nothing - perhaps they are resting.
the productive vine
I think this vine has been luckier than the other. Whereas the unproductive vine has had to struggle and soar high into the tree-tops, the productive vine has only needed to make a little vertical growth to emerge into sunlight, over the top of the garden wall.
what to do?
My guess is that I will need to prune the northerly vine severely and bring it forward and lower.
In the case of the southerly vine, I believe all I need to do is to prune fairly normally. Though it is the usual practice to train vines along wires, I don't think I need to do that. In the wild, vines climb to reach the best light and, as my vine is already doing this, and is producing fruit, I will let it continue.
Most of the information that I found online related to vines in the USA, where the weather conditions are generally more extreme than in the UK and grape varieties are different. In the USA, vines seem to be propagated using ripe wood. I will try this, but will also be trying cuttings with leaves, as I have done before. In the UK, it has also been the practice to propagate using a single bud on a short length of ripe stem buried horizontally. I believe that worked before, so I will be trying it again.