Organic Answers Column – February 12, 2025 – Sweet Potatoes v. Yams

Sweet Potatoes or Yams: Which is Which?

Sweet potatoes at harvest time, South Dakota U Extension

A question that comes up regularly illustrates one of the difficulties when it comes to knowing the difference between sweet potatoes and yams: there are producers of sweet potatoes who wanted to label them as yams because of the color of the product they were growing was so different from usual colors. According to an informational page at the University of Mississippi State Extension:

You won’t find many true yams in U.S. grocery stores because they require specific growing conditions found in the Caribbean. Yams are commonly grown in Africa, South America, and Central America. Although you can find canned potatoes that are marketed as yams, you’ll notice that they are also labeled as sweet potatoes and the first ingredient is sweet potatoes. The U.S. Department of Agriculture requires this dual labeling when sweet potatoes are labeled as yams.

Sweet potatoes are a New World plant, and Ipomoea batatas is a member of the morning glory family Convolvulaceae. Take a look at the flowers and you can see the family resemblance. The plant is remarkably responsive to the development of cultivars so there are many sizes and shapes of sweet potato but they are all still Ipomoea batatas with the variety name attached. Many of these are patented, including many of the fancy leafy vines that are planted for ornamental purposes. Sweet potatoes are more more plump and moist, and more prolific than yams, producing 4-10 roots per plant versus 1-5 tubers per yam plant.

Left, Yams from Ghana (by Edith Obayaa, via Wikimedia); Right, Beauregard sweet potatoes (by Llez via Wikimedia)

More about the differences from a North Carolina State University archival page:

In the United States [the terms “yams” and “sweet potatoes”] are used interchangeably but refer to what are really sweet potatoes. On the other hand, there is a plant called a yam that is not even closely related to a sweet potato. . . A true yam is rare to find in grocery stores because it is a plant that is mostly grown and consumed throughout the tropics. Yams are grown in Africa and South and Central America. True yams are a starchy, dry tuber that is scaly in appearance and typically has white flesh. They are best apapted to tropical climates and do not perform well in our climate.

Bookmark this topic to have handy when the “are these yams or sweet potatoes?” question comes up at the Thanksgiving table.

Sweet potatoes are grown for both the variety of cultivars for food as well as ornamental vines.
(Potato varieties l-r, Jewell, Oriental, Jersey, Garnet; photo from CA sweet potato council.)

Varieties (patented and not) https://potatoes.cals.ncsu.edu/sweetpotato/sweetpotato-varieties/

https://en.wikipedia.org/wiki/List_of_sweet_potato_cultivars

Ornamental sweet potato vines take on many colors and can spread over
large distances. Photo by Maggie Dwyer.

Now that you know the crop you’ll be growing this spring is sweet potatoes, here is some basic information for planting them:

Sweet potatoes do the best in acid sandy soils but will grow fairly well in all soils. The sweet potato weevil is not much of a problem in sandy soils. Loose, well-drained soil is needed. Use moderate amounts of compost, lava sand, and soft rock phosphate. Sweet potatoes are fairly drought-tolerant once established. Mulching is important to help maintain an even soil moisture. Mulch will also keep the vines from rooting. Without mulch, the vines should be moved every 7-10 days. Vines will root in good soil and make potatoes if not moved. After the second month of growth, try to keep the soil as evenly moist as possible, but not overly wet.

Visit the Dirt Doctor’s Sweet Potatoes page for more information, such as how to start your own slips to plant.