Pass the sweet potatoes please!Question: Can you tell us the difference between sweet potatoes and yams? Can we grow them here?

Answer: Yams and sweet potatoes are terms used interchangeably in the U.S. Confusion with the terminology started several decades ago when orange-fleshed sweet potatoes were introduced in the southern U.S. and producers and shippers wanted to distinguish them from the more traditional white-fleshed types.

The African word "nyami," referring to the starchy, edible root of the Dioscorea genus of plants, was adopted in its English form, yam. Yams in the U.S. are actually sweet potatoes with relatively moist texture and orange flesh. Although the terms are used interchangeably, the U.S. Department of Agriculture requires that the label "yam" always be accompanied by "sweet potato."

The sweet potato (Ipomea batatas) is distinctly different from potato (Solanum tuberosum) and yam (Dioscorea spp.) which are also grown and marketed in America. While sweet potatoes are commercially grown in the southern U.S., some varieties have been developed that can grow in the southern fringes of the northern states, and require a minimum of 130 frost-free days in order to produce a crop.

Yam is a tropical crop important in north China, Japan, and West Africa, and only in the most southern regions of Florida. In contrast to sweet potatoes, yams are dry, starchy, and light-fleshed. They are also much larger than a sweet potato, growing to between 3 to 8 pounds each. There are several other differences. True yams have rough, scaly skins with a long, cylindrical shape (some have toes) and because they contain more starch then sweet potatoes, they aren't as sweet.

Sweet potatoes have thin, smooth skins that, depending on the variety, vary in color from a pale yellow to a deep purple, to a vivid orange. Their short, blocky, shape has tapered ends with flesh colors that vary from light yellow to pink, red, or orange.

Grocers will often refer to the two types of sweet potatoes as dry (yellow fleshed) and moist (orange fleshed), although those terms do not accurately reflect moisture content. Growers cure both types of sweet potatoes by storing them in warm, moist rooms for about ten days before they are sent out to the stores. This helps to preserve them longer, gives them a darker color on the outside, and helps to convert their starch to sugar which makes them sweeter when cooked as well as giving them a smoother texture. Generally, only sweet potatoes harvested after October are cured.

According to the North Carolina Department of Agriculture, one cup of cooked sweet potatoes provides 30 mg of beta carotene (vitamin A). It would take 23 cups of broccoli to provide the same amount.

Sweet potatoes are a great source of vitamin E and they are virtually fat-free, which makes them a real vitamin E standout. Most vitamin E-rich foods, such as vegetable oils, nuts and avocados, contain a healthy dose of fat.

The Nutrition Action Health Letter rated 58 vegetables by adding up the percentage of USRDA for six nutrients (vitamins A and C, folate, iron, copper, and calcium), plus fiber. Sweet potatoes topped the list with a whopping 582 points; its nearest competitor, a raw carrot, came in at 434.

Sweet potatoes are a good source of dietary fiber, which helps to promote a healthy digestive tract. Sweet potatoes have more fiber than oatmeal.

Sweet potatoes are virtually fat free, cholesterol free and very low in sodium. A medium sweet potato has just 118 calories!

In our cool, coastal climate, growing either sweet potatoes or yams would most likely provide disappointing results. Most cultivars require a minimum frost-free period of 120 to 150 days, with a minimum average daily temperature of 77 degrees F. Even the new introductions, requiring a growing season of just 90 days, would not grow well due to the lack of heat units.

EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: baiter1@pacifier.com.

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