I've had grapevine around in my families yards all my life. We had 3 plants
that grew very well and had such sweet green AND purple grapes. We never did anything to them but cut them every year!!
Over the last 8 years I have had one good old vine in my yard along the side of the house, it produces VERY well, and all I ever do is ignore it. I might go out there during the summers to give it some water when the temps reach over 100 but other then that...I do nothing at all. Think of the them as the hermits of the fruit family. They like to be left alone, not 'tended' too, and every once in a while to be checked on, oh and they like to have their 'children' leave when they are 'of age'.