Reviving an old grape, possibly choked by a privet
I'm posting a lot these days, as I've just bought a house in coastal Northern California with remnants of an old fruit garden. (Spent roughly thirty years under brambles, now those brambles are cleared and the garden is reemerging.) Current question is about grapes:
There is a grape vine that is at least thirty years old and about twenty feet long, rather thick for the snaky vine that it is. Has been in shade under trees and blackberries, but still putting off leaves and a little fruit (small, light-colored, sweet with seeds). I've cleared the brambles and plan to train it over a horizontal trellis to create a ceiling of grapes for a sitting area. Wondering if/how I should prune it, and other measures I should take to revive it.
One thing: on a previous post people suggested cutting it back to zero. The problem is that a) the original plant is now in a shaded area; its vines are what's in the sun now and b) a damned privet has grown up in the same spot as the original (see photo below)--a privet which I suspect is compromising the grapes, but which my neighbor would like to keep. Help?