One grapevine planted several years ago now yields more grapes than I can ever harvest. This year I was able to reach four quarts of grapes for eating. They are sweet and crunchy. You know they are ready to harvest when the grapes are soft and springy, if they feel hard then they need more time on the vine. They seem to last quite a while in the refrigerator. Yes Muscadine grapes have seeds in them unless you are able to get a variety without seeds.
