Botanical Names: Dioscorea (several different species)
Many use the words yam and sweet potato interchangeably in parts of the U.S. and Canada. However, they are not the same and come from different botanical families. It is often referenced that this confusion began with the early settlers called the sweet potato by the wrong name and it’s still happening today.
Yams have a rough, scaly skin that is often harder to peel when compared to sweet potatoes. The skin is typically brown with the flesh being white. There are eight different species of yams and all can be found for sale in different parts of the United States, but the Chinese Yam (Dioscoreaopposita) is the most widely distributed.
Yams are related to ornamental grasses and lilies and are native to Africa and Asia. There are over 600 different varieties of yams and 95% of the food crop grows in Africa. These perennial, herbaceous vines that are cultivated for consumption are not grown in the United States, but in Africa, Asia, Latin America and the Caribbean. Since yams cannot be grown in the U.S., here are the instructions on growing sweet potatoes, which are able to grow in different climates of the U.S.
Adding more confusion to the name game, one of the cultivars of sweet potato is called ‘White Yam’ due to its brown skin and white flesh. This variety is also referred to as ‘Triumphs’, ‘Southern Queen’, ‘Poplar Root’, ‘Choker’ or ‘White Bunch’. It is one of the oldest varieties in the America’s and very unusual, but still, a sweet potato is not a yam.
Sweet potatoes grow from slips, not seeds like most vegetables. Slips or rooted cuttings are sprouts that have matured to about 8 to 10 inches long, then cut just below the leaf joint to produce roots. Purchase certified disease-free slips from online garden sources, local garden centers and hardware stores. Sweet potatoes need a spot that is warm and well drained, with rich fertile soil that has a pH of 5.5 to 6.5. Plant slips in May to June when the soil has warmed, in earthed-up rideges.
If slips are not available, as an alternative place tubers with sprouting eyes in sandy, free-draining soil. Plant at a depth of 2 to 3 inches. Row spacing and distance would depend directly on the variety selected. Note that sweet potatoes need lots of water, but are susceptible to rot if the soil is not well draining. Once established, fertilize every two to three weeks with a high-potash fertilizer to encourage tuber growth. Typically, harvest the sweet potatoes 85 to 100 days after planting. A telltale sign for mature sweet potatoes is when the vines begin to yellow, generally 4 to 5 months after planting. For harvesting, use a garden fork and gently lift the soil, trying not to spear the roots. It is important to cure the tubers. Find a warm spot, such as a shed, garage or basement where the air is warm. After two weeks, the sweet potatoes will lose sufficient moisture and keep for a month or so without sprouting. If not used within a month, bake, peel and freeze for maximum use throughout the year. Never store raw sweet potatoes in the refrigerator.
Some pests and diseases are frequent problems for sweet potatoes. They include sweet potato weevils and pathogenic nematodes. Fungal diseases can attack stored tubers. If you suspect any pests or diseases, it is best to contact your local university extension service for control methods available in your area.