Confusion over sweet potatoes is somewhat common. It is often confused with the yam, and the names are used interchangeably depending on where you are. The sweet potato, Ipomoea batatas, often has moist, sweet, orange-red flesh, while the yam, Dioscorea species, often has dry, starchy, yellowish white, potato-like flesh. The sweet potato has a much wider appeal to gardeners because of its versatility and delicious flavor.
Planting Sweet Potatoes
Sweet potatoes are grown from slips, or rooted cuttings, not from seed. The slips can be bought from a garden center or via mail order. Once you’ve grown a crop of sweet potatoes, you can overwinter the roots for the next year’s crop. Don’t bother with trying to grow slips from sweet potatoes bought at the grocery store. They are treated to prevent sprouting.
To produce slips for the coming season, start three months before the last frost date by placing a sweet potato in a glass that is half full of water. One-third of the tuber should be immersed in the water. Place the glasses in a warm, sunny location to sprout. When the newly-formed sprouts are at least six inches long, gently pull them off and set them in water or damp sand until they develop a root system of their own.
Once the slips are rooted and hardened off, they can be planted out about two weeks after the last frost, once the soil has warmed. The night temperatures should be at least 60 degrees Fahrenheit. Plant the slips to the first set of leaves, about 12 to 18 inches apart, in mounded hills in rows. The rows should be about three feet apart. Sweet potatoes can be grown closer together. If you plant them closer, you'll get smaller, but more tubers.
Growing Sweet Potatoes
Sweet potatoes need full sun and at least 100 warm days and nights to produce decent tubers. Even the lightest frost will kill the plants, so make sure not to plant the slips too early. The soil should be moist and well drained.
Hilling the soil helps to keep the tubers warm and improves drainage. Laying a dark plastic mulch over top of the mounds, with the vines poking through, will help colder region gardeners raise the soil’s temperature. Top growth might be slow to start, but once they get rooted in and the daytime temperatures heat up, their growth will become vigorous. Once the vines begin to develop, make sure to cultivate underneath, or lift them occasionally, to prevent the vines from rooting in, which will only create competition for the main set of roots. Otherwise, sweet potatoes are very self-reliant and require very little effort until harvest. Fertilize with compost or manure tea, only if necessary, about six weeks after planting.
Harvesting Sweet Potatoes
Sweet potatoes can be harvested as soon as they are large enough to use. For the best flavor, wait until the foliage, or top portion of the plants, is killed off by a light or moderate frost. Once this has taken place, harvest the roots immediately. Remove the tubers carefully with a garden fork so you don’t bruise them. Bruised tubers should be used first, while the rest can be stored for long periods. If you’re going to store them, they should be cured first. Let them sit in the sun for a day, separated and dry, then place them in a humid location out of direct sunlight for roughly 2 weeks. Once the curing stage is complete, store the tubers in a dry, cool location for up to 5 months.
Sweet Potato Problems and Pests
Sweet potatoes are rarely bothered by pests or diseases, but might experience leaf spot, sooty mold, black rot on the base of the stem or brown rot on the tuber itself. Rotate crops every 4 years to ensure the consistency of pH in the soil, to discourage fungal and bacterial problems. If flea beetles are a problem, cover the tops of the plants with a floating row cover.