As per Darlene's suggestions about summer pruning, I have cut the second year vines to encourage growth down the trellis. I have also cut the grass to help keep weeds down and reduce the competition for nutrients the vines need. I'm not sure if allowing the lawn mower to through the grass cuttings onto the ground under the vines is a good idea or not. In this photo the weeds still seem to be under control ... it won't stay that way!