Learn about planting sweet potatoes, sweet potato slips and even a purple sweet potato in this detailed look at sweet potatoes.
Columbus had no idea how much he would change the world when he landed on what he thought was the East Indian island shore. Thanks to his confused sense of geography, several garden staples spread across the world, notably maize, tomatoes, peppers, Irish potatoes, and the unsung hero of the garden — sweet potatoes.
Sweet potatoes, or yams as many people call them, create more than a little confusion with their name. They’re not yams at all — African vegetables related to lilies, which are never grown in America — and they aren’t even related to Irish, or “true,” potatoes, either. They are, however, the first vegetable to be called “potato,” thanks to their Native American name, “batatas.” Their botanical name, Ipomoea batatas, reflects that early name.
Ipomoea includes morning glories and some moonflowers as well as two edible cousins, Asian native water spinach, and Man-of-the-Earth, a North American wildflower. The broader family, Convolvulaceae, contains more than 2,700 species across 85 genera.
The sweet potato is a groundcover vine originally from tropical Central and South America. Its vines tumble rampantly across the ground, but cannot climb wires or structures like morning glory or cypress vines. A sweet potato’s roots are a fibrous mass, stretching 8 feet or more from its crown. Like potatoes, the sweet potato is often called a “tuber”; more accurately, it’s a “tuberous root,” a thickened section of root, without a potato’s eyes.
Sweet potatoes display an astonishing diversity. Their leaves can be shaped like hearts, arrowheads, palmetto fronds, or just about anything in between. Leaf color can be just as varied, ranging from pale lime green to purplish-black. The potatoes can also be white, yellow, orange, pink, red or purple.
After Columbus carried sweet potato roots back to the Spanish Court, batatas quickly became all the rage on Europe’s banquet tables. On the other side of the globe, Spanish trade galleons sailing to the Orient carried sweet potato provisions, and colonies in the Philippines planted sweet potatoes in great quantity.
As Spanish and Portuguese traders and slavers sailed around the globe, sweet potatoes traveled with them, sailing to India, Africa, and the rest of Polynesia. Today, the sweet potato has become a main foodstuff in many countries. However, none can compete with Papua New Guinea, where the annual consumption averages 1,100 pounds of sweet potatoes per person.
As a result of American slavery, sweet potatoes secured their place in southern soul food, and at the same time, orange-fleshed varieties came to be known as “yams.” Slaver ships traveling the Middle Passage of the Atlantic carried tremendous stores of African yams, which were fed to the brutally imprisoned humanity below decks. Sweet potatoes so closely resembled these yams that slaves treasured them as a taste of their stolen homeland.
Sweet potatoes are a super food as well as soul food, as they are fat free, low in calories and rich in vitamins and minerals. One cup of orange-fleshed sweet potato contains a double dose of vitamin A, 35 percent of a day’s supply of vitamin C, 26 percent of daily fiber, and more beta-carotene than any other source. A cup of the tender greens holds 125 percent of the daily allowance of vitamin K.
Sean Thomas of Living Energy Farm in Louisa, Virginia, supplies sweet potato slips to Southern Exposure Seed Exchange for the company’s online catalog, offering 14 varieties of sweet potatoes. He recommends the following:
• Ginseng is a productive sweet potato well-adapted to Virginia. It delivers light orange roots, sometimes with purple streaks, with high beta-carotene content and a traditional sweet flavor, beneath vines with lobed leaves.
• Sweetie Pie is a new selection developed by Doug Jones at Piedmont Biofarm in North Carolina. Sweetie Pie produces many large roots in clay soils too dense for other varieties. This is another orange-fleshed variety, with heart-shaped leaves.
• For shorter seasons, try Carolina Ruby. Ruby, a daughter of Georgia Jet, provides sweet, creamy orange roots in about 115 days. According to Thomas, commercial growers who typically grow Covington sweet potatoes have been taking notice of Carolina Ruby recently.
• Violetta, Sean’s favorite variety, is a purple-skinned, white-fleshed root. While many whites tend to share characteristics with Irish potatoes, Violetta is described as sweeter and nuttier by comparison. It delivers a crop in 120 days.
• For a purple-fleshed sweet potato, take a look at All Purple, a Japanese variety. This is a dry, starchy, slightly sweet root that stores well.
Sweet potatoes grow well in gardens across most of the United States, and even into Southern Canada, with a little help. In frost-free zones, sweet potatoes are an herbaceous perennial; gardeners treat them as annuals in most of the U.S. With the right varieties and a little effort, sweet potatoes can be grown as far north as USDA Zone 3. They don’t have many demands — beyond heat, lots of heat.
Plan on planting your sweets a full month after your last frost date. They need warm soil as well as warm days and nights for rapid growth and root production. Plant them too early, and they will either produce lots of vine and few roots, or simply refuse to grow at all.
Sweets aren’t very particular about soil quality, either, growing well in rich or poor soils; they do produce best in sandy or loamy soils. Dense clay soils are more likely to cause twisted, oddly shaped roots, but the roots will still taste the same.
Sweet potatoes are not started from seed, but rather from slips, or rooted cuttings. Many gardeners produce their own.
The unassuming sweet potato possesses surprising super qualities and abilities. It crossed the globe, changed the world, and saved thousands of people from starvation and malnutrition. This humble root has changed the course of history; cultures have built their entire diet upon its foundation. It brings much more than Thanksgiving candied yams to the table, and all because Columbus took a shortcut.
Interested in more tips? Check out Growing Sweet Potatoes.
Starting sweet potato slips is easy to do. A week or two before your last frost, select a small, sound root, preferably one already sprouting. Cover it partially with potting mix, large end down, in a pot or bowl, or suspend it in a jar of water: Either method works well. While potting mix will protect the root from rotting, children get to watch the feeder roots form in water.
Place the root in bright indirect light, in a warm place. Roots will soon form, followed shortly by vines, or slips. The slips can be broken off and planted after they have formed at least three full leaves.
If the vines get overly long waiting for the garden to warm, trim them into smaller cuttings. One long vine can yield several smaller slips.
Andrew Weidman, Lebanon, Pennsylvania, has been researching and writing about historic vegetables for years. He is a member of the Back Yard Fruit Growers and has served as a county Master Gardener.
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