Sweet potato vines produce their potatoes underground, rather than on the vines that grow above ground. Sweet potatoes are well insulated underground, after all. If you can’t harvest sweet potatoes right away, cut those dead vines off at the ground so the decay doesn’t pass to the tubers below. “Sweet potatoes definitely grow well here in the mountains,” says Joe Evans, owner of Paper Crane Farm in Marshall. How to Grow Sweet Potatoes. Sweet Potatoes grow under the ground just like regular potatoes.However, that is the end of their resemblance to each other. Sweet potato, yam, carrot, beet, radish, jicama, turnip, cassava, ginger, turmeric, galangal and parnsip are only some of them. Unlike regular potatoes, Sweet Potatoes are a warm-weather crop and need about 4 months of high temperatures to mature. The varieties grown as vegetables will produce mature sweet potatoes ready to be dug up in 95 to 150 days after the slips are set out in the garden. Above ground, Sweet Potatoes are sprawling vines that can take up a lot of room in the garden. Collectively they are called root vegetables. The truth is once those vines blacken with frost bite, the answer to when to dig sweet potatoes becomes — Right Now! Yes, potatoes grow underground and so do a lot of vegetables. “I’d say our main challenge compared to the Piedmont is the cold. Sweet potatoes will grow in poor soil, but deformed roots may develop in heavy clay or long and stringy in sandy dirt.