See that your Vines, having all their roots inside, do not suffer for want of water. Remove the surface-soil down to the roots, and then cover them with 4 inches of fresh turfy loam, mixing with it half a bushel of hone-meal to every cubic yard. In spring lay over this 3 inches of fresh horse or cow droppings, and during summer water with guano at the rate of two ounces to every gallon of water. If, as you seem to suspect, poverty is the cause of your Vines being so weak, this will put some fresh vigour in them.