Grow Your Best Series: Sweet Potatoes!

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Being the top sweet potato producing state in the country, we rarely face a shortage of NC-grown sweet potatoes. Sweet potatoes (Ipomoea batatas) are in the morningglory family. They are rewarding and relatively easy to grow. One plant can produce 2.5 lb of sweet potatoes, and 20 feet of row can produce 100 lb or more.

Most commercial production is in eastern NC but we can grow them well in the mountain region as well. Sweet potatoes love heat, so if you’re at a higher elevation, consider growing them in black grow bags, next to a warm brick wall or in dark soil rich with organic matter that will absorb more heat. They will do best in looser soils such as bottomland free of root-knot nematodes, or in raised beds.

Popular orange flesh varieties include Beauregard, Covington, Jewel, Georgia Jet, and Porto Rico. These vary in root size, uniformity, and days to maturity. Their skin and flesh color vary slightly as well. Bonita, White Hamon, and O’Henry have cream-colored flesh. Japanese purple have purple skin and white flesh. All-purple varieties have purple skin and purple flesh. NC State University has long been a source of improved sweet potato genetics. Sweet potatoes are grown from a “slip”- a vegetative cutting from a sprout growing from a root. Purchase slips from a reputable slip supplier and do not grow slips from diseased roots. If you produce your own slips, do not use diseased roots to grow as diseases such as scurf can be passed on through diseased slips. If you purchase slips before you are able to plant, place slips, root side down, in moist potting media, until you are ready to plant.

Plant in spring after any danger of frost, once soil temperatures average 65°F. Incorporate lime and fertilizer prior to planting according to soil test results. Plant slips cut edge down, 9-15” between slips, in ridged rows 3-6’ apart. Plant 4-5” deep if possible, and be sure to bury 2-3 nodes on the slip. Maintain consistent soil moisture after planting and provide 1” water per week with rainfall or irrigation. Keep your sweet potatoes weed-free with 1-3” straw mulch, or by cultivating 1-2 times before the vines start running. Eventually, healthy vines will cover the soil and you only need remove weeds that may pop up from time to time. Sweet potatoes do well in black plastic mulch, though you must remove plastic prior to harvest. If you are growing on a large scale, consider using biodegradable plastic mulch, which will break down or be easier to remove by harvest.

Most sweet potatoes take 100-120 days to mature. Harvest before frost, when foliage has started to yellow. To harvest, cut the vines away from the crown, rake away any mulch, and loosen roots with a shovel or fork placed far enough away from the roots to avoid damage. Dig around each plant to be sure you have removed all tubers. Wash soil off and cure in a warm (85- 90°F) place with high humidity and good air circulation around each root for 2 weeks before eating or placing in storage. Store sweet potatoes in a dark place with temperatures above 55°F. It is easier to harvest during dry soil conditions, so monitor weather forecasts and harvest ahead of heavy rains, if possible. If you cannot dig your crop before the first frost, you should at least cut the foliage from the crown ahead of the frost to minimize injury to the root.

Voles, and wireworms, and sweet potato flea beetle are a few important pests of sweet potato. Wireworms are click beetle larvae that live in the soil. They feed on roots and will leave pinholes. To reduce wireworm damage, do not plant sweet potatoes in a place that was lawn or had another grass, such as corn or sorghum, growing the previous year. Sweet potato flea beetle feed on foliage, and their larvae will also damage roots, leaving tunnels on the surface of roots. Remove weedy hosts such as bindweed and morningglory, and avoid planting in areas where corn, small grains, or beets were grown previously. Practice crop rotation and till in any residues of these crops at the end of the season to destroy overwintering and egg-laying sites. If they are a persistent problem, consider planting resistant varieties Jewel or Centennial. Voles are always a challenge. They chew holes in the roots as they mature. The damaged sweet potatoes can still be cured and eaten, with chewed area removed, but are obviously not marketable. Keep a clean strip of bare soil around the sweet potato bed. Reduce populations by setting mousetraps baited with peanut butter if they are problem. Deer feed readily on sweet potato foliage, so consider appropriate fencing if your local deer enjoy venturing into your garden.

With further questions about growing sweet potatoes or other gardening questions, contact the N.C. Cooperative Extension, Wilkes County Center at 336-651-7333.