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The Sweet Potato

The soft orange sweet potato is often mislabeled a “yam” in parts of North America. The sweet potato is botanically very distinct from a genuine yam. The genus Ipomoea that contains the sweet potato includes several garden flowers called morning glories. The sweet potato is not a potato or even a distant cousin. Potatoes are tubers; sweet potatoes are roots.
The plant is an herbaceous perennial vine bearing alternate heart-shaped or palmate lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple. Sweet potato varieties with white or pale yellow flesh are less sweet and moist than those with red, pink or orange flesh.
The center of origin and domestication of the sweet potato is thought to be either in Central America or South America. Sweet potatoes were domesticated at least 5,000 years ago. In South America, Peruvian sweet potato remnants dating as far back as 8000 BC have been found. Sweet potatoes are now cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth. The majority comes from China, with a production of 105 million tons. About half of the Chinese crop is used for livestock feed. In the U.S., North Carolina, the leading state in sweet potato production, provided 38.5% of the 2007 U.S. production of sweet potatoes. In 2007, California produced 23%, Louisiana 15.9%, and Mississippi 19% of the U.S. total.
Sweet potatoes provide twice the recommended daily allowance of vitamin A and more than one-third of the daily requirements of vitamin C. They are an important source of beta-carotene, vitamin B6, iron, potassium and fiber. Studies consistently show that a high intake of beta carotene-rich vegetables and fruits can significantly reduce the risks for certain types of cancer. Sweet potatoes contain virtually no fat or sodium.
Sweet potatoes that are a pretty, bright, orange color are richest in beta-carotene.
The orange tuber packs 438% of your daily value of infection-fighting vitamin A. Like carrots, sweet potatoes are a major source of skin-protecting beta-carotene. While bananas are often touted as the go-to source of potassium, a medium sweet potato has 28% more potassium than a banana. Potassium helps your body absorb fluids to replace sweat losses.)
Besides simple starches, sweet potatoes are rich in complex carbohydrates, dietary fiber, beta-carotene, vitamin C, and vitamin B6. Pink, yellow and green varieties are high in carotene, the precursor of vitamin A. In 1992, the Center for Science in the Public Interest compared the nutritional value of sweet potatoes to other vegetables. Considering fiber content, complex carbohydrates, protein, vitamins A and C, iron and calcium, the sweet potato ranked highest in nutritional value. According to these criteria, sweet potatoes earned 184 points, 100 points over the next on the list, the common potato. Despite the name “sweet”, it may be a beneficial food for diabetics, as preliminary studies on animals have revealed it helps to stabilize blood sugar levels and to lower insulin resistance. While sweet potato provides less edible energy and protein per unit weight than cereals, it is a higher nutrient density source of certain vitamins and minerals than cereals.
Although the leaves and shoots are also edible, the starchy tuberous roots are by far the most important product. Sweet potato leaves and shoots are a good source of vitamins A, C, and B2 (riboflavin).

The plant does not tolerate frost. It grows best at an average temperature of 24 °C (75 °F), abundant sunshine and warm nights. Annual rainfalls of 750–1,000 mm (30–39 in) are most suitable, with a minimum of 500 mm (20 in) in the growing season. The crop is sensitive to drought at the tuber initiation stage 50–60 days after planting, and it is not tolerant to waterlogging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor.
Depending on the cultivar and conditions, tuberous roots mature in two to nine months. Sweet potatoes rarely flower when the daylight is longer than 11 hours. They are mostly propagated by stem or root cuttings or by adventitious roots called “slips” that grow out from the tuberous roots during storage. They grow well in many farming conditions and have few natural enemies; pesticides are rarely needed. Sweet potatoes are grown on a variety of soils, but well-drained, light- and medium-textured soils with a pH range of 4.5-7.0 are more favorable for the plant. They can be grown in poor soils with little fertilizer. Sweet potatoes are very sensitive to aluminum toxicity and will die about six weeks after planting if lime is not applied at planting in this type of soil. They are sown by vine cuttings rather than seeds. The rapidly growing vines shade out weeds and little weeding is needed.
In the Southeastern United States, sweet potatoes are traditionally cured to improve storage, flavor, and nutrition, and to allow wounds on the periderm of the harvested root to heal. Proper curing requires drying the freshly dug roots on the ground for two to three hours, then storage at 85–90 °F (29–32 °C) and 90 to 95% relative humidity from five to fourteen days. Cured sweet potatoes can keep for thirteen months when kept at 55–59 °F (13–15 °C) and >90% relative humidity. Colder temperatures injure the roots.
Cuttings of sweet potato vine, either edible or ornamental varieties, will rapidly form roots in water and will grow in it indefinitely in good lighting with a steady supply of nutrients. Sweet potato vine is ideal for use in home aquariums, trailing out of the water with it’s roots submerged, as it’s rapid growth is fueled by toxic ammonia and nitrates, a waste product of aquatic life, which it removes from the water. This improves the living conditions for fish, which also find refuge in the vast root systems.
Researchers at North Carolina State University are breeding sweet potato varieties that would be grown primarily for biofuel production.

Candied sweet potatoes are a side dish consisting mainly of sweet potatoes prepared with brown sugar, marshmallows, maple syrup, molasses, orange juice, marron glacé, or other sweet ingredients. Often served in America on Thanksgiving, this dish represents traditional American cooking.

In South America, the juice of red sweet potatoes is combined with lime juice to make a dye for cloth. By varying the proportions of the juices, every shade from pink to black can be obtained.