Harvesting sweet potatoes
In late summer, approximately 12 to 16 weeks after planting them, you will notice that the foliage and stems begin to turn yellow and die back.
Now is the time to start harvesting your sweet potatoes, although they can be left in the ground longer if you prefer larger tubers.
Make sure that you lift them before the first frosts though, to avoid the tubers being damaged by the cold. Lift them with a fork taking care not to bruise them.'via Blog this'