we really hacked ours back last year due to renovations in the garden and this year we've got the most grapes we've ever had.it grows over a pergola and the bunches are hanging down through the roof as well as everywhere else. i regularly cut off all the leaves which are shading the sun from getting to the grapes, and also the runners which seem to grow overnight. you can't really hurt a grapevine too much, they just keep on growing. rain at the right time, and sun at the right time are what we've found has the most influence on grape production.