Sweet potatoes can be harvested as soon as they are large enough to eat. They must be harvested before the first frost of autumn since the colder temperatures damage the sweet potatoes even though they are underground.
Sweet potatoes should be harvested on a day that is dry but overcast. This minimizes the chances of infection and damage that can result if the sweet potatoes are exposed to sun or rain during harvest.
The best tool to use for harvesting sweet potatoes is a spade fork. It should be used gently, starting a few feet away from the plant to avoid damaging the plant's roots.
The harvested sweet potatoes should be allowed to dry on the ground for a few hours and then sorted and stored for curing in a warm, dark place with good ventilation. Properly cured sweet potatoes have a sweeter flavor than fresh sweet potatoes.