The sweetpotato (Ipomoea batatas) is a warm-season crop that is not planted until well after the last chance of frost in the spring. The soil temperature should be above 65 °F before planting this crop.
|Piedmont||May 1-June 15||Not recommended|
|Coastal||April 15-June 15||Not recommended|
Sweetpotatoes do not produce tubers but produce an edible storage root that is developmentally a true root derived from root tissue. They grow best in a well-drained, loamy to sandy soil. Those grown in heavy clay soil may be smaller and misshapen. Till organic matter into the garden to loosen and improve the aeration and drainage of heavy clay soils.
Plant sweetpotatoes 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 (called slips) in rows 3 feet apart with 8 to 12 inches between plants in the row at a depth of 3 to 4 inches. Water in transplants using a high phosphorus starter fertilizer according to label directions.
Sweetpotatoes grow from plants or sprouts called “slips” produced from the roots of the previous season’s crop. Most gardeners prefer to buy sweetpotato slips rather than producing their own, but these slips are sprouts that are easy to grow from stored sweetpotatoes. Roots from last year’s home harvest or those that were organically grown are more apt to sprout and make slips as compared with most grocery store sweetpotatoes, which were chemically treated to not sprout during storage.
Producing Sweetpotato Slips
Start with healthy, medium-sized sweetpotato roots and regular or wide-mouthed quart jars. Insert 3 or 4 toothpicks into each root halfway between its two ends. Place a root into each jar allowing the toothpicks to rest on the rim of the jar. Add water to each jar until the bottom half of each root is submerged. Place the jars in a warm location with indirect sunlight. Watch the water levels and add water as needed to keep the lower halves submerged. Change the water weekly to reduce problems with bacterial growth in the water, which will appear as cloudiness. Sprouts will appear in about 2 weeks.
Once the sprouts are six or more inches long, grasp each sprout near its base and pull or twist the sprout free from the mother sweetpotato root. Place these sprouts into another jar with enough fresh water to cover their bottom ends. This will allow them to produce their own roots, which takes about 10 days. These rooted sprouts, now called slips, may be held in water until planting time or potted into containers for added root and leaf growth before planting into the garden. Plant slips at a depth of 3 inches.
- ‘Beauregard’ (90-100 days) has a light rose skin, moderately deep-orange, very sweet flesh, great flavor, and is consistent in shape. It is the quickest to produce harvestable roots. It is resistant to some of the important sweetpotato diseases but is not resistant to root-knot nematodes or bacterial soft rot in storage. It has moderate resistance to flood damage, but its roots may be misshapen. Stores well.
- ‘Centennial’ (100-110 days) is smooth and moist textured with deep orange flesh. It is resistant to root-knot nematodes and wireworms.
- ‘Covington’ (PP #18,516) (95-110 days) from NCSU has a great, sweet flavor and good yield. Storage ability is better than with Beauregard. Roots are very uniform in shape and not prone to misshapen or long, narrow roots. It has rose-colored, smooth skin and orange flesh. Yields are similar to Beauregard. Resistant to russet crack, Southern root-knot nematodes, and Fusarium wilt, and is moderately resistant to Streptomyces soil rot.
- ‘Excel’ has light copper skin with orange flesh. It is a high yielder (15% more than Jewel) with excellent baking and canning qualities and stores well. This variety has high resistance to Southern root-knot nematodes, stem rot or wilt disease, and to internal cork.
- ‘Jewel’ (120-135 days) has deep copper skin and deep orange flesh. It is high-yielding with good Fusarium wilt, Southern root-knot nematodes, sweetpotato beetles, and internal cork resistance. Stores well.
- ‘Mahon Yam’™ (PP #20,666) (90 days) is a sweetpotato and not a yam. It has pink skin and an extra sweet, orange, stringless flesh with a slightly drier texture than Beauregard. The flavor is excellent, and the yield is very good with uniform, cylindrical roots. Storage is excellent when properly cured.
- ‘Murasaki’ (100-120 days) from LSU has bright purple skin and light-colored flesh. Plants have vigorous vines (grows 20′). The flesh is less creamy than other sweetpotatoes, and the texture is flakier with a nutty flavor. It is highly resistant to Southern root-knot nematode and Fusarium soil rot
- ‘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, Southern root-knot nematodes, and many insect pests. This combination of resistance makes it an excellent cultivar for the home gardener because fewer pesticides may be needed.
- ‘Southern Delite’ (100 days) 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 diseases and insect pests.
- ‘Sumor’ (110-120 days) 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 resistant to root-knot nematodes and many insect pests.
- ‘Vardaman’ (100 days) produces high yields of smooth, oval, rich orange-fleshed roots that separate easily from the plant at harvest. It has a compact, bush-type growth habit. It is susceptible to soil insects and nematodes but has some resistance to Fusarium wilt.
It is best to base fertilizer applications on the results of a soil test. Please see HGIC 1652, Soil Testing, for more information. If a soil test is not taken, apply 5-10-10 fertilizer preplant at 30 pounds per 1,000 square feet and till into the soil. Sidedress with 4 pounds of 5-10-10 per 100 feet of row before the vines cover the row. For measuring small amounts of fertilizer, a pint container holds approximately a pound of most fertilizers.
Sweetpotatoes 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 sweetpotatoes. 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.
Weeds, Diseases, & Insect Pests
Weed control is important until the plants cover the row. Cultivate shallowly to prevent root damage. Most diseases and insects are not a problem in the home garden. However, home gardeners may experience a problem with wireworms and root-knot nematodes. A crop rotation with corn the following year may help reduce a root-knot nematode problem, as will the use of nematode-resistant varieties. For additional information on cultural control of root-knot nematodes, see HGIC 2216, Root-Knot Nematodes in the Vegetable Garden, and for more information on insect pests and their control, please see HGIC 2215, Sweetpotato & Irish Potato Insects.
Disease problems typically are reduced by using a two-year rotation between sweetpotato crops. Do not use transplants with spots of black rot on the lower stems. For more information on diseases and control, see HGIC 2214, Irish & Sweetpotato Diseases.
Sweetpotatoes should be ready to harvest about 90 to 120 days after planting. Harvest the sweetpotatoes when 30 percent of the roots are larger than 3½ inches in diameter. Harvest before frost because cool soil temperatures can reduce the quality and storage capacity of the sweetpotatoes. When harvesting, it is best to cut and remove the vines before digging. Be careful while digging and handling the sweetpotatoes, the skins are easily damaged, and the roots are easily bruised.
Sweetpotatoes require curing 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 sweetpotatoes 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 sweetpotatoes 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 sweetpotatoes. Sweetpotatoes can be stored under good conditions for over six months.
Sources of Sweetpotato Slips
Filaree Farms 509-422-6940
Gurney’s Seed 513-354-1491
Johnny’s Seed 877-564-6697
New Sprout Organic Farms 828-357-5501
Park Seed Co. 800-845-3369
Sandhill Preservation 563-246-2299
Southern Exposure Seed Exchange 540-894-9480
Sow True Seed 864-254-0708
Stark Bros. 800-325-4180
Steele Plant Company 731-648-5476
Document last updated on 4/22 by Sarah Oswald Scott.
Originally published 02/00