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.)
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||May 10-June 10||---|
|Central||May 1-June 15||---|
|Coastal||April 15-July 1||---|
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.
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.
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.
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.
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.
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.
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.
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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