Okay there has to be someone on here that knows the answer to this. I'm growing them for the first time this year--got slips for a 90 day variety that went in the ground in midMay. They are doing well, growing all over the place but I want to know when I can start harvesting them--don't want to wait til it gets too close to frost but don't want to dig them too early either. Any hints? The place where I got the slips--Johnny's--just said to dig them anytime they are as big as I want them but I don't really know where to find them. I grow regular potatoes and just dig down with my hands by the main stems to steal them when I need them until the vines die then I dig. Not sure when to start on these critters. Thanks. Here's what the sweet potato patch looks like.