Sweet potatoes, or yams, were originally a tropical plant, which explains its need for warmth. Sweet potatoes need a long, hot growing season of usually more than 100 days of hot weather [source: Ellis]. This plant also doesn't like cold soil. For these reasons, sweet potatoes do better in southern climates and can be tricky for areas that have cold nights during the growing season. Northern growers might have a better chance at getting a successful crop by growing the plants in raised beds with row covers to protect the seedlings from the cold.