Bob,
Are you grafting at 85-90 degrees and cutting to drain sap every couple of days? Not sure if you saw Jason’s experiment Grafting grapes onto wild rootstock. The hardest part I have is finding a spot for the right conditions. Grapes are just very difficult to learn to graft but the experts are getting nearly 100% take rates. Seems crazy to me they are doing that well! In Kansas we are still way to cool with this fluctuating weather. We are barely warm enough now to graft whips. I’m worried about pears and apples in this weather so grapes are a definite no for me at the moment. By the end of the week we are close to grape range again. I made one apricot graft but the temperatures have been all over the place. I didn’t graft cherries this year and will tbud those later.