Do you cut them back each year? That helps the nutrients stay strong. Not many grapes will grow, or no grapes, if there isn't enough nutrients. For the same reason it could have to do with the soil and what type of trees and other plants are around it because they could be stealing the nutrients. I flat out love the muscadine grape!!! I read about it after my heart attack a little over two years ago. I was determined to find a muscadine grape seed supplement and it has done absolute wonders for my health. It has truly given me my life back!!!