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Alert: Making Pesticide Applications in School/Community Gardens

Sweet Potato

Sweet potato, Ipomoea batatas, is a tender, warm-weather vegetable that requires a long frost-free growing season to mature large, useful roots. Sweet potato is native to Central and South America. It is one of the most important food crops in tropical and subtropical countries, where both the roots and tender shoots are eaten as a vital source of nutrients. Commercial production in the United States is mainly in the southern states, particularly North Carolina and Louisiana.

Sweet potatoes, which are related to the morning glory, grow on trailing vines that quickly cover the soil, rooting at the nodes along the way. "Bush" varieties with shorter vines are available for situations where space may be limited.

Though orange-fleshed varieties are most common today, white or very light yellow-fleshed types were once considered the finest types for sophisticated people. Some white-fleshed types are still available, though they may be hard to find outside the Deep South.

For their ornamental value, sweet potatoes are often grown as ground cover or in hanging baskets, in planters and even in bottles of water in the kitchen. Cut-leaf types exist that are particularly attractive. The sweet potato is rich in vitamin A. It is not related to the yam, though in the marketplace the two names are often used interchangeably. The true yam, Dioscorea sp., is an entirely separate species that grows only in the tropics.

Recommended Varieties

Beauregard (100 days to harvest, light purple skin, dark orange flesh, extremely high yielder from Louisiana State University)

Bush Porto Rico (110 days, compact vines, copper skin, orange flesh, heavy yield)

Centennial (100 days; orange skin, flesh; good keeper; resistant to internal cork, wilt)

Georgia Jet (100 days, red skin, orange flesh, somewhat cold tolerant)

Jewell (100 days, orange flesh, good yield, excellent keeper)

Sumor (ivory to very light yellow flesh, may be substituted for Irish potatoes in very warm regions)

Vardaman (110 days, golden skin, orange flesh, compact bush type, young foliage purple)

Commercial production is currently dominated by Jewell in North Carolina and Beauregard in Louisiana.

When to Plant

Sweet potatoes are started from plants called "slips." Transplant the slips as soon as the soil warms up after the last frost to allow the maximal warm-weather growing period. Always buy plants grown from certified disease-free roots. To grow your own plants, place several sweet potato roots about one inch apart in a hotbed and cover with two inches of sand or light soil. Add another one inch of sand when the shoots begin to appear. Keep the soil in the bed moist throughout the sprouting period, but never allow it to become waterlogged. Keep soil temperature between 70° and 80°F. Plants are ready to pull in about 6 weeks (when they are rooted and 6 to 8 inches tall). You can allow roots to continue possibly producing additional flushes of plants if more are desired. The sprouts (slips) are planted directly in the garden from the sprout bed.

Spacing & Depth

Set the plants 12 to 18 inches apart, preferably on a wide, raised ridge about 8 inches high. A ridge not only dries better in the spring but also warms earlier than an unridged area. Black plastic mulch can be a good way to speed early season growth by capturing and storing more of the sun's heat in the soil under the plastic cover. Because the vines of spreading varieties need a great deal of space, allow at least 3 to 4 feet between rows.

Care

After early cultivation (which is not necessary with black plastic), sweet potatoes need minimal care to keep down weeds. Once the vines spread to cover the ground, little weeding is required. Irrigate if an extended drought occurs. Do not water during the last 3 to 4 weeks before harvest to protect the developing roots.

Harvesting

Early roots may be "robbed," starting in late summer, by digging into the side of the ridge and carefully removing some developing roots while leaving the plant in place. Dig the main crop of sweet potatoes around the time of the first frost in the fall. Use a spading fork or stout shovel and be careful not to bruise, cut or otherwise damage the roots. Dig below the level of the ridge and gradually move closer toward the plants, removing soil until the fat roots are exposed. Carefully dig under these roots to gauge the depth to dig as you go down the row.

Proper curing can be a problem in the cool fall season. Ideally, the roots should be allowed to dry on the ground for 2 to 3 hours, then placed in a warm room for curing (85°F and 85 percent humidity (if possible) for 10 to 14 days and then stored in a cool (55°F) location. Sweet potatoes should be handled as little as possible to avoid scuffing and bruising. In case of frost, cut the vines from the roots immediately to prevent decay spreading from the vines to the roots and dig sweet potatoes as soon as possible. Cold soil temperatures quickly lessen the roots' ability to keep in storage. Do not allow roots drying in the garden to be frosted because they are quickly ruined. For best quality, use the potatoes as soon as possible after they have been stored.

Common Problems

To prevent diseases, plant varieties with multiple resistance, use "certified" plants and rotate sweet potatoes' location in the garden.

At certain sites, mice may become a problem by burrowing into the mound and eating the tasty, nutritious roots before harvest can commence. Check for evidence of mouse infestation regularly and apply appropriate control measures as needed.

Questions & Answers

Q. My sweet potato roots are covered with black splotches in the skin. What can I do to prevent this condition?

A. This condition is probably caused by a disease known as "scurf" that is superficial in the skin of the root. The sweet potatoes are still good to eat, although they may not keep as well in storage. Check for varieties resistant to this problem.

Q. Why did my sweet potato roots grow long and stringy instead of short and plump?

A. Too much rain, irrigation or poorly drained soil prevents proper root formation. Sweet potatoes prefer hot, dry weather once the vines cover the ground.

Q. What makes sweet potatoes crack and split?

A. Heavy rains or too much irrigation during the final 3 to 4 weeks before harvest may cause the roots to split, especially if conditions have been dry for a period before late water application begins.

Q. Are sweet potatoes ruined if the vines were frosted before digging?

A. No, but they should be harvested immediately. The length of time that they can be stored may be reduced and some experts say that taste and quality of the roots may be adversely affected.

Q. What are yams?

A. Moist-fleshed cultivars of sweet potato are often called "yams" in stores, but sweet potatoes are not yams - they belong to the morning glory family (Convolvulaceae). The true yams belong to the Dioscoreaceae family. These vary greatly in size and need a long, warm growing season. In addition, they grow only in the tropics.