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Sweet potato slips can be planted safely in most parts of the state around May 1. Several leaves should be exposed above the soil line.
Photo by S. Cory Tanner
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When digging up sweet potatoes in the fall, handle them carefully to avoid damaging their tender skin. Let the roots dry in the sun for an hour or two, then pick them up and gently brush away the loose soil. Do not wash the potatoes until you are ready to cook them.
Photo by S. Cory Tanner
Southern gardeners to beautiful above-ground vines all summer and an underground bounty at harvest time. All they need from you are warm temperatures, good soil and a nice, long growing season.
Let’s get our terminology straight first. Sweet potatoes are not tubers; they are tuberous roots—basically, swollen storage roots. To the horticulturist, calling a sweet potato a tuber (a common blunder) is like confusing a limerick and a haiku to the poet: of little real consequence, but irritating. Yams are also totally unrelated plants.
Sweet potatoes are related to morning glories and produce vigorous, attractive vines. The ornamental varieties make great additions to flowering containers and borders, but their tuberous roots are generally inedible. Many edible sweet potato types, however, feature darkly colored leaves and stems and sometimes flowers that will complement the annuals in your landscape.
As with most root crops, soil preparation is the key to success. Sweet potatoes like the well-draining, sandy soils of the coastal plain, but with a little upfront effort, they do well in red clay. In heavy clay, till 2 inches of compost well into topsoil before planting to loosen and improve the soil. Otherwise the roots may be smaller and misshapen. If your soil is really poor, consider growing the crop in raised beds or containers.
Sweet potatoes are typically planted as root sprouts, called “slips,” grown from last year’s crop. Buying slips from your local garden supply or a mail-order source is easier than growing your own. I don’t recommend growing sprouts from grocery store roots, which are often treated to prevent sprouting; they may harbor pest or disease issues.
Sweet potatoes need a growing season of about 90 to 150 days, depending on variety. Transplant slips once all danger of frost has passed and the soil is at least 65 degrees. Set slips 3 to 4 inches deep with 8 to 12 inches between plants and 3 feet between rows. Keep the newly planted slips well watered until new vine growth begins. Established vines benefit from an inch of water each week.
Watch out for vines that root down, robbing energy from the main crop and producing undersized sweet potatoes. You can encourage good-sized roots near the crown by simply lifting or kicking aside longer vines occasionally to prevent rooting.
In late September, check root size by digging a plant. You want to harvest the crop when 30 percent of roots are 3 to 4 inches in diameter or larger. If the soil gets too cool (less than 55 degrees) or frost threatens, the roots lose quality and won’t store well. Harvest carefully; fresh sweet potato roots skin and bruise easily.
Perhaps the biggest challenge for home gardeners is curing sweet potatoes. Curing converts some of the starches into sugars, heals wounds, toughens skins and prolongs storage life. Years ago, many rural South Carolinians had a “sweet potato house” designed for just this purpose. Today we recommend curing the potatoes in the warmest room of your house (usually the kitchen) for two weeks. The temperature must be above 70 degrees or the roots won’t cure at all.
Store cured potatoes in a cool, dark location, not below 50 degrees and never in the refrigerator. Mine are in the crawl space under my house. Properly dug and cured sweet potatoes will keep for more than six months in good condition.
Learn more about growing sweet potatoes at Clemson Extension’s Home & Garden Information Center.
S. CORY TANNER is an area horticulture agent and Master Gardener coordinator for Clemson Extension based in Greenville County. If you have any questions or comments, you can email him here.