Sweet Potato

Prepared by Susan James, Agricultural Assistant, Richland County; and Bob Polomski, Extension Consumer Horticulturist, Clemson University. Revised by Joey Williamson, HGIC Extension Agent, Clemson University. (New 02/00. Revised 12/04.)

HGIC 1322

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Planting

The sweet potato (Ipomoea batatas) is a warm-season crop that should not be planted until well after the last chance of frost in the spring. The soil temperature should be above 65 °F before planting this crop. Sweet potatoes are produced from plants or sprouts called "slips" produced from the roots of the previous season's crop and from vine cuttings. Most gardeners prefer to buy transplants.

Piedmont: Abbeville, Anderson, Cherokee, Chester, Edgefield, Fairfield, Greenville, Greenwood, Lancaster, Laurens, McCormick, Newberry, Oconee, Pickens, Saluda, Spartanburg, Union and York counties.
Central: Aiken, Allendale, Bamberg, Barnwell, Calhoun, Chesterfield, Clarendon, Darlington, Dillon, Florence, Kershaw, Lee, Lexington, Marion, Marlboro, Orangeburg, Richland and Sumter counties.
Coastal: Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Hampton, Horry, Jasper and Williamsburg counties.

Sweet potatoes grow best in a well-drained, loamy to sandy soil. Those grown in heavy clay soil may be smaller and misshapen. Plant sweet potatoes on ridges in the Coastal and Piedmont areas to provide better drainage. In the Central part of the state, do not plant in ridges if the soil is sandy. Plant the transplants in rows 3 feet apart with 8 inches between plants in the row at a depth of 4 inches. Water in transplants using a high phosphorus starter fertilizer according to label directions.

Recommended Cultivars

• Beauregard has a light rose skin, moderately deep-orange flesh, and is consistent in shape. It is resistant to some of the important sweet potato diseases, but is not resistant to nematodes.
• Centennial is smooth textured with deep orange flesh. It is resistant to root-knot nematode and wire worm.
• Excel has light copper skin with orange flesh. It is a high yielder with excellent baking and canning qualities and stores well. This variety has high resistance to southern root knot, stem rot or wilt disease and to internal cork.
• Jewel has deep copper skin, and deep orange flesh. It is high yielding with good wilt and root-knot nematode resistance.
• Regal has brilliant purplish-red skin with dark orange flesh. It is similar to Jewel, with higher yields. It is resistant to internal cork and Fusarium wilt or stem rot, pox or soil rot, and the southern root-knot nematode. This combination of resistances makes it an excellent cultivar for the home gardener because the use of pesticides can be reduced
• Southern Delite has rose to dark copper skin. It is a high yield with excellent baking flavor. It has high levels of resistance to a wide array of disease and insect pests.
• Sumor has smooth yellowish to light tan skin with white to yellow flesh. It is not very sweet and can be prepared similarly to a standard white potato. It has good field resistance to Fusarium wilt or stem rot and is also resistant to root-knot nematodes.
• Vardaman produces high yields of smooth, oval, orange-fleshed roots that separate easily from the plant at harvest. It is susceptible to soil insects and nematodes.

Fertilization

It is best to base fertilizer applications on the results of a soil test. If a soil test has not been taken, apply 5-10-10 fertilizer at 30 pounds per 1,000 square feet. Sidedress with 4 pounds of 5-10-10 per 100 feet of row before the vines cover the row.

Watering

Sweet potatoes need uniform watering with at least 1 inch of rainfall or irrigation water per week for normal growth. Water sufficiently to moisten the soil to a depth of at least 6 inches. Rainfall or irrigation after a long dry period may result in cracking of the sweet potatoes. Water is especially vital during transplant establishment and root development. To reduce the incidence of disease, always water the crop in the morning, so that the leaves will dry before dark.

Cultural Practices

Weed control is important until the plants cover the row. Cultivate shallowly to prevent root damage. Diseases and insects are, usually, not a problem in the home garden. Wireworm and root-knot nematodes may be a problem. Rotation with corn may help to reduce a root-knot nematode problem, as will the use of resistant varieties. Disease problems can be reduced by a two-year rotation between crops. Do not use transplants with spots of black rot on the lower stems. For addition information on cultural control of root-knot nematodes, see HGIC 2216, Root-Knot Nematodes in the Vegetable Garden.

Harvest

Sweet potatoes should be ready to harvest about 120 days after planting. Harvest the sweet potatoes when 30 percent are larger than 3½ inches in diameter. Harvest before frost because cool soil temperatures can reduce the quality and storage capacity of the sweet potatoes. When harvesting, it is best to cut and remove the vines before digging.

Be careful while digging the sweet potatoes, as they will skin very easily. Also avoid rough handling as the sweet potatoes are easily bruised.

Curing

Sweet potatoes should be cured to heal wounds and to convert some of the starch in the roots to sugar. The optimal conditions for curing are to expose the roots to 85 °F and 90-percent humidity for one week. Few home gardeners can supply these conditions, so place the sweet potatoes in the warmest room in the house, usually the kitchen, for 14 days. No curing will occur at temperatures below 70 °F.

Storage

After curing, store the sweet potatoes in a cool location. Never expose them to temperatures below 50 °F and never refrigerate them. Temperatures below 50 °F will result in off flavors and possibly rot the sweet potatoes. Sweet potatoes can be stored under good conditions for over six months.

Problems

Insects and diseases are usually not very trouble-some in the home garden. Wireworms and root-knot nematodes may be a problem. Rotate with corn to help reduce a root-knot nematode problem. Also, use resistant varieties. Disease problems can be reduced by a two-year rotation between crops. Do not use transplants with spots of black rot on the lower stems.

Excerpted from Home Vegetable Gardening, EC 570, 2002.

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