Growing Sweet Potatoes

Nutritious and high-producing, sweet potatoes are a rewarding root crop to grow.

| Fall 2015

The sweet potato is a delicious and generous root crop. It is a plant with the potential to prevent measles and childhood blindness in Africa, and has been referred to as “food that ends famine quickly” in a Hawaiian proverb. It is a heroic plant, with an illustrious future ahead of it as an affordable and nutritious food source that can withstand harsh growing conditions, yet much of the history of this valiant root crop remains a mystery. Could this humble root, most famously found hiding under a blanket of marshmallows on the Thanksgiving dinner table, have a super-food secret identity?

Although they are native to the same geographic location, the sweet potato and the “Irish potato” are not closely related. The sweet potato is actually a member of the morning glory family, while the “Irish potato” is a close relative of tomatoes and eggplants. Many refer to the sweet potato as a tuber, which is a thickened stem much like the tubers of a regular potato plant. In fact, sweet potatoes are the swollen and starch filled roots of the sweet potato plant, not a stem at all.  Finally, the most muddled sweet potato myth: the yam, sweet potato or not? Often a fleshy southern variety of sweet potato is incorrectly referred to as a yam. The yam is actually an African native tuber that is related to lilies and grasses It has a much thicker stem, it cannot tolerate temperatures below 68 degrees Fahrenheit and it grows much larger than sweet potatoes. The confusion began when southern farmers decided to call their sweet potato variety yams in order to set their varieties apart from Northern varieties. 

Much confusion surrounds the history and origins of the sweet potato. Carbon dating has taught us that the sweet potato has been domesticated in Central America for at least 5,000 years. However, a wild ancestor of the domesticated root has never been found. The exact native range of the wild sweet potato ancestor remains a mystery. However, there is now strong evidence that the sweet potato may be native to the Yucatán Peninsula of Mexico and the Orinoco River of Venezuela. This theory stems from the fact that there is a great deal more molecular diversity in sweet potatoes from this area than in South America, where the sweet potato was first observed by Europeans.

Sweet potato and the “regular” potato, as well as corn managed to catch the eye of Spanish conquistadors in the 1400s. The sweet potato was immediately recognized as an exotic delicacy when introduced to Europe. Conversely, the starchy white potato was not embraced in Europe until well after the sweet potato was established. After its 1492 introduction to Europe, the sweet potato spread to Africa by the 1500s, and to North America and Asia by the 1600s.

Europeans are credited with the dispersal of the sweet potato and many other crops from the Americas to the rest of the world. However, an entirely different group of people have been found to have visited South America and brought this botanical jewel home for cultivation. It has been discovered that Polynesians had been cultivating a South American variety of sweet potato at least four hundred years before Europeans.

Captain James Cook visited Polynesia in the 1760s. He was fascinated to find civilizations inhabiting far flung islands far into the Pacific Ocean. Cook returned to London with samples of the sweet potatoes that he had found Polynesians cultivating. The genetic makeup of these 18th century sweet potato remains were recently examined and found to be from AD 1000 to AD 1100. The potato remnants are believed to have descended from Peruvian and Ecuadorian varieties. This piece of living evidence suggests that Polynesians made an incredible 5,000 mile journey to South America, and returned to the Pacific Islands to cultivate the crop. There is also compelling linguistic evidence to back up this almost unbelievable theory. There is a close relation between the words “Kuumala”, the Polynesian name for sweet potato, and “kumara”, a native South American word for the same root.

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