Sweet potatoes belong in the "Convolvulaceae," or morning glory family, as is evident by their morning glory-type blossoms.
Illustration By Keith Ward
(For details on growing many other vegetables and fruits, visit our Crop at a Glance collection page or check out our Food Gardening Guide app.)
Sweet potatoes (Ipomoea batatas) are productive, delicious and super-nutritious. Few staple crops keep as well as these flavorful tubers, which can be stored for months in a cool, dry place. This crop is a staple in climates with hot, muggy summers, but growing sweet potatoes is also possible in cooler climates if you adjust to meet the plants’ requirement for warm temperatures.
Types of Sweet Potatoes to Try
Sweet potato varieties differ in skin and flesh color and texture, as well as in leaf shape and vine length. The flavor and nutritional qualities of sweet potatoes vary with flesh color: Orange-fleshed sweet potatoes are rich sources of fiber and vitamins A and C. White-fleshed varieties contain less vitamin A, but are a good source of minerals and B vitamins. Purple sweet potatoes contain a little vitamin A, but are loaded with antioxidants.
Orange-fleshed sweet potatoes are the most popular. Tried-and-true ‘Beauregard’ is productive and disease-resistant. Some short-vined varieties, such as ‘Georgia Jet,’ make good crops in areas where summers are brief. In warmer areas, grow slower-maturing heirlooms famous for flavor, such as ‘Nancy Hall.’
White-fleshed sweet potatoes are easier to grow and store in warm climates compared with regular “Irish” potatoes. Fun to use in the kitchen, white sweet potatoes are distinctly creamy, making them a favorite for soups and baby food. Varieties of this type also make excellent potato salad.
Purple-fleshed sweet potatoes need a long, warm season to produce a good crop, but the starchy, deep-purple roots of varieties such as ‘Violetta’ and ‘All Purple’ are worth the wait. The dry flesh of purple sweet potatoes makes them perfect for roasting and frying. The anthocyanin pigments that give purple sweet potatoes their color also enhance their nutritional value.
For more information about sweet potatoes, see our Sweet Potatoes at a Glance chart.
When to Plant Sweet Potatoes
To grow sweet potatoes, begin with rooted stem cuttings, called “slips,” which sprout from the ends of stored tubers. If you want to grow your own slips, move parent potatoes to a warm room in early spring. A month before your last frost date, soak the tubers in warm water overnight, and then plant them sideways or diagonally in shallow containers, covering the tuber only halfway with sandy potting soil. After danger of frost has passed, move the sprouting sweet potatoes to a warm spot outdoors and keep them moist. When handled this way, stems (the slips) will emerge from both ends of the sweet potato, with each potato producing six or more. When the stems are more than 4 inches long and the weather is consistently warm, break off the slips from the parent sweet potatoes and plant them.
Planting Sweet Potatoes
Sweet potatoes grow best in warm, well-drained soil with a slightly acidic pH between 5.6 and 6.5. Choose a site with fertile soil in full sun. Where summers are mild, place plastic, either black (heats soil and prevents weeds) or clear (heats more than black but does not control weeds), over the site in spring to warm the soil. Plant slips into small holes cut in the plastic, and leave plastic on the site until harvest time. Sweet potatoes benefit from a generous helping of fully rotted compost dug into the soil before planting, along with a light application of balanced organic fertilizer. Space bush-type varieties 12 inches apart, but allow 18 inches between varieties that grow long, vigorous vines. Space rows at least 3 feet apart; long-vined varieties may need even more space. Situate sweet potato slips diagonally in prepared soil, so that only the top two leaves show at the surface.
Water well and frequently for the first several days and be patient. After about two weeks, the plants should be well-rooted and showing hardy growth. For even more information on growing sweet potatoes, especially in cooler climates, visit Grow Sweet Potatoes – Even in the North.
Harvesting and Storing Sweet Potatoes
Begin checking the root size of fast-maturing varieties 90 days after planting. Sweet potatoes can be left in the ground as long as the vines are still growing and nighttime temperatures are above 50 degrees Fahrenheit. One sign sweet potato plants are done growing is when the leaves and vines turn yellow. Starting from the outside of the row, loosen the soil with a digging fork before pulling up the plants by their crowns. Some sweet potato varieties develop a cluster of tubers right under the plants, but others may set roots several feet from the main clump.
Before storing sweet potatoes, you will need to cure them, a process that creates a second skin that is an incredibly effective seal. To cure sweet potatoes, gently arrange them in a single layer in a warm, humid place where temperatures can be held at 80 degrees for seven to 10 days. In warm climates, a well-ventilated outbuilding is ideal. In cooler climates, a bathroom or closet with a space heater makes a good curing place (put a bucket of water in the room to increase humidity). Another option is to place jugs of hot water in a large cooler with your tubers; add new hot water to the jugs daily to keep the space warm and humid.
After curing, choose damage-free sweet potatoes for long-term storage in a dry place where temperatures will stay between 55 and 65 degrees. The flavor and nutritional content of sweet potatoes improves after a couple of months of storage. If conditions are ideal, well-cured sweet potatoes will store for up to 10 months.
Pest and Disease Prevention Tips
Slightly acidic soil conditions help suppress sweet potato diseases, and the plants’ lush vine growth naturally smothers many weeds. Rotating sweet potatoes with grains, cowpeas or marigolds helps prevent disease problems, especially from root-knot nematodes, which infect tomatoes, peppers and many root crops. Avoid growing sweet potatoes in areas recently covered with grass, because ground-dwelling grubs and wireworms — often numerous in grass-covered soils — chew holes and grooves into the tubers. Deer love to eat sweet potato leaves, so you may need row covers or other deterrents. Stored sweet potatoes are a favorite of hungry mice, so stash your harvest in a secure location.
Some sweet potato varieties produce morning glory-type flowers in late summer, followed by tiny seeds. Plant breeders work with the seeds, but for gardeners, propagating sweet potatoes by growing them from slips is more practical.
With adequate moisture, shabby-looking slips usually recover quickly.
You can also increase your supply of plants by taking 4-inch-long stem-tip cuttings, clipping off all but the top two leaves, and rooting the cuttings in moist potting soil.
In the Kitchen
Sweet potatoes can be baked, boiled, mashed or used in stir-fries. Cooked, mashed sweet potato can be substituted for pumpkin in any recipe, and few desserts are as nutritious as sweet potato pie. In breads and puddings, use cinnamon, nutmeg, cloves or orange to add complexity to sweet potato flavor. In savory dishes, sweet potatoes’ flavor is enhanced by a range of spices, including garlic, ginger and curry, and sweet potato salads can carry big handfuls of chopped parsley or cilantro. Thin slices of sweet potato are great for grilling, or you can make sweet potato chips in a hot oven. Don’t overlook the new leaves on stem tips, which make excellent cooked greens.
Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on Google+.