How do I know when to try digging my sweet potatoes? I planted them late, maybe mid-June or early July or so. So I doubt they are ready yet, but how will I know? Also, where should I dig to find the tubers themselves? Close to the base stem? Finally, I didn't realize the 'vines' would run, can I put up poles next year for the yams to run up? And when would be the best time to plant them next year?