Sweet potatoes are a tender, warm-season perennial plant grown as an annual. Set sweet potato starts or slips in the garden after all danger of frost has passed in spring, usually 4 weeks after the last average frost date. Sweet potatoes grow best where the air temperature remains very warm, from 75° to 95°F throughout the growing season. Sweet potatoes are best started indoors as early as 12 weeks before they are placed in the garden. Sweet potatoes require from 100 to 150 days to reach harvest.
Description. The sweet potato is a tender vining or semi-erect perennial plant grown for its swollen fleshy tuber, similar to an elongated potato. Tubers vary from creamy-yellow to light brown to deep red-orange in color and from 4 or 5 inches to 8 inches or more in length. The flesh of the tuber is yellow or gold. Tubers are described as “dry” and “moist” noting the texture of the tuber when eaten. “Moist” sweet potatoes are often called yams; however, a true yam is actually a different species found in tropical regions. The flower of the sweet potato is pink to purple colored. Tubers grow underground from the vine’s central shoot.
Yield. Grow 5 sweet potato plants for each household member.
Site. Plant sweet potatoes in full sun. Grow sweet potatoes in loose, well-worked, well-drained somewhat sandy soil with aged compost added. Soil that is overly rich will produce more foliage than tubers. Remove all soil lumps, rocks or other obstacles that might cause tubers to become deformed. Sweet potatoes prefer a soil pH of 5.0 to 6.5.
Planting time. Set sweet potato starts in the garden after all danger of frost is past in spring, usually about 4 weeks after the last frost. Sweet potatoes are extremely sensitive to frost and need a warm, moist growing season of as many as 150 days. Sweet potato slips can be started indoors as early as 12 weeks before they are transplanted into the garden. Well-rooted sweet potatoes require a soil growing temperature of 60° to 85°F and an air growing temperature of 65° to 95°F. Sweet potatoes will thrive in air temperatures as high as 100°F.
Starting sprouts or slips. Grow sweet potatoes from rooted sprouts, or slips, taken from a mature tuber. Here are two ways to start sweet potato slips: (1) Place a sweet potato in a jar of water that is half full with about one-third of the tuber submerged. Leave it in a warm (75°F), sunny location where it will sprout. When sprouts are 6 inches long, pull them off the tuber and set them in water or damp sand until they root. Start about 12 weeks before you plan to set the slips in the garden. (2) Place cut seed pieces (tubers divided into pieces each with one or more “eyes”) in a hotbed of moist sand or light growing medium with a constant temperature of about 80°F. Set the pieces about 1 inch apart and cover with 2 to 4 inches of sand or light soil. Shoots will appear in about 3 weeks then add another inch of sand or light soil; do not let the growing medium dry out. When sprouts reach 3 to 4 inches tall reduce the temperature to 70°F and grow on for another 3 weeks. Seed tubers will be rooted in about 6 weeks and can then be planted in the garden.
Planting in garden. Set rooted slips in the garden on mounded rows 12 inches wide and 8 inches high; space rows 3 feet apart; plant slips at 12 inch intervals.
Water and feeding. Sweet potatoes will tolerate dry soil once established but will produce best if kept evenly moist, an inch of water every week until 3 to 4 weeks before harvest. Sweet potatoes prefer well-drained soil; tubers will rot in soil that is too wet. Add aged compost to planting beds before planting; add a low nitrogen fertilizer (5-10-10) to the soil two weeks before planting.
Companion plants. Grow sweet potatoes with other root crops: beets, parsnips, and salsify.
Care. Sweet potatoes are easily trained onto trellises, lattice, or wires strung between sturdy poles.
Container growing. Grow a single sweet potato plant in a box or tub that is at least 12 inches high and 15 inches wide. Use a light, porous soil mix. Place a stake or trellis in the center to support the vine which grow up and outwards.
Pests. Insects are not likely to attack sweet potatoes in northern regions. In southern regions, sweet potato weevils and wireworms are common pests. Plant resistant varieties. Where infestations occur remove all plants and do not re-plant in that area for three years.
Diseases. Sweet potatoes are susceptible to root rot and fungus disease. Plant disease-resistant varieties and keep the garden clean of debris and weeds where pests and disease can harbor. Remove and destroy infected plants immediately before disease can spread to healthy plants.
Harvest. Lift sweet potato tubers when they have reached full size, when leaves and vines have begun to yellow and wither. Sweet potatoes require from 100 to 150 days to reach harvest. Carefully dig plants using a garden fork starting about 10 to 15 inches from the center of the vine and work inwards lifting. Be careful not to bruise the tubers which are thin skinned. Complete the harvest before the first frost in fall; tubers are damaged by freezing or cold weather.
Varieties. Beauregard (moist-fleshed, 100 days); Boniato (dry-fleshed, 120 days); Centennial (moist-fleshed, 110 days); Georgia Jet (moist-fleshed, 100 days); Goldrush (140 days); Jasper (150 days); Jewel (moist-fleshed, 100 days); Nancy Hall (moist-fleshed, 110 days); Porto Rico (moist-fleshed, 110 days); Southern Delite (moist-fleshed, 100 days); Vardaman (moist-fleshed, 110 days); White Yam (dry-fleshed, 120 days); Yellow Jersey (dry-fleshed, 120 days).
Storing and preserving. Cure (dry and harden) sweet potatoes in the sun for 3 to 4 hours after lifting then move to a dark, humid place at 80° to 85°F for 10 to 15 days; then store at 55° to 60°F in a dry, cool place for 4 to 6 months. Sweet potatoes can be frozen, canned, or dried.
Common name. Sweet potato, yam
Botanical name. Ipomoea batatas
Origin. Tropical America and Caribbean
Grow 80 vegetables: THE KITCHEN GARDEN GROWERS’ GUIDE