Sweet potatoes grow in the ground, where the edible portion of the plant develops beneath the soil’s surface. This crop is an important staple food across many parts of the world, valued for its starchy, sweet-tasting underground structure. As a tropical plant, it requires a long, warm growing season to produce a substantial harvest.
The Core Difference: Root vs. Tuber
The edible part of the Ipomoea batatas, or sweet potato, is botanically classified as a “storage root” or “tuberous root,” which is a distinction from a true “tuber.” Storage roots are formed from the plant’s fibrous, lateral roots that swell to store starches and sugars for the plant’s energy needs. These roots do not possess nodes or internodes, which are characteristic features of stems.
In contrast, the common white potato is a true tuber, which is an enlarged, underground stem segment called a stolon. This stem origin means white potatoes have “eyes,” which are actually buds located at the nodes that can sprout new growth. Sweet potatoes, as true roots, lack these organized buds, though they can sprout new shoots, or “slips,” from adventitious buds.
How Sweet Potatoes Are Planted and Grow
Sweet potatoes are not grown from seeds or by planting a whole root like a potato, but rather by planting specialized sprouts called “slips.” A slip is a vine cutting or shoot, often developed by suspending a sweet potato in water or placing it in soil until it sprouts. These slips are then transplanted into the soil after the danger of frost has passed, when both the air and soil temperatures are reliably warm.
The above-ground portion of the plant develops into vigorous, sprawling vines with heart-shaped leaves, similar in appearance to its relative, the morning glory. These leaves perform photosynthesis, generating the energy that is then transported down to the underground roots. This energy causes the lateral roots to thicken into the fleshy, edible storage roots that are harvested. Optimal growth requires well-drained, loose soil, often sandy, and a long, frost-free growing period, typically ranging from 90 to 150 days.
Harvesting and Curing the Crop
Sweet potatoes are typically ready for harvest when their foliage begins to yellow, or just before the first expected frost. It is important to harvest before the soil temperature drops below 55°F, as cold soil can negatively affect the flavor and storage quality of the roots. Because the skin is delicate and bruises easily, the roots must be dug up carefully, starting a foot or more away from the main plant to avoid damage.
Once harvested, sweet potatoes must undergo a process called “curing” before they are stored or eaten. Curing involves holding the roots in a high-heat and high-humidity environment, usually 80–85°F with 90–95% relative humidity, for about five to seven days. This process promotes the healing of any minor nicks or scratches on the skin, which extends the root’s shelf life. Additionally, the heat triggers the conversion of starches within the root into sugars, which develops the characteristic sweet flavor.