Farmers Weekly Review

Every year about mid-October, I get a very specific call from homeowners when they start emptying out their tired containers of annuals. I know just what the call will be when I see the message “sweet potato vine-edible?”
As the gardener digs out what is left of that hanging basket, if they planted any of the ornamental sweet potato vines, they are surprised to find a fleshy, up-to-fist-sized underground stem that vaguely resembles a potato. Could it be? That the sweet potato vine produced an actual sweet potato?
Well. Yes, indeed.
This long, attractive bold vine in darkest purple “Blackie” or the bright chartreuse “Marguerite,” are really sweet potatoes, and produce a tuber. But edible?
So, this falls under the category of what exactly does edible mean. Is it safe to eat an ornamental sweet potato vine tuber? Yes. Is it palatable and delicious. Absolutely not. That is the magic and science of food cultivation.
It depends what the goal is of the agricultural scientist working on cultivation. For the ornamental sweet potato vines that are great “spiller” plants added to containers, the focus became selecting plants for their showy foliage and flowers, and less on the underground modified stem — which is not tasty.
But does that mean you shouldn’t save that tater-looking structure? No, you should save it to get a free larger, more robust plant for spring. Store the ornamental sweet potato fleshy root in a cool, dark, non-freezing corner of the basement.
Because along with your cannas, gladiolas and other tender fleshy roots and bulbs, you can repot the ornamental sweet potato in March, and let it start growing again for the coming year.
But all this talk of sweet potatoes got me thinking to talk about the other question I get in November. Just what is the difference (if there is any) between sweet potatoes and yams? And the difference couldn’t be bigger, unless you ask the USDA.
Sweet potato, yam, yam, sweet potato. The terms are used interchangeably, like dressing and stuffing. But they are really different plants, and I doubt you have ever really had a yam, no matter how many times Aunt Mildred calls them that.
The differences between sweet potatoes and yams are significant. Sweet potatoes belong to the morning glory family Convolvulaceae and are dicots (having two seed leaves); yams belong to the Dioscoreaceae, related to lilies, which are monocots (think one-seed leaf like grasses, lilies and onions). And the difference doesn’t stop there.
Sweet potatoes are known for their sweet flavor and soft texture (when cooked). Yams are very starchy and less sweet. Sweet potatoes also come in four different color combinations (inside/outside). The one most people are familiar with is the rose-colored skin with orange flesh. Beauregard is the most common variety planted commercially.
Beauregard is known for its high disease tolerance and high yield, and matures relatively quickly. Sweet potatoes require a long growing season; Beauregard is considered a fast grower at 90 to 100 days.
The top growing sweet potato state is North Carolina, with its hot, humid climate. In 2023, they produced 16.9 billion pounds of sweet potatoes. We can grow sweet potatoes here in Illinois, but our fickle weather doesn’t get hot and stay hot (and moist) long enough for big crops.
There are three other varietal colors sweet potatoes come in, but these are far less common: pale copper-tan skin with white flesh; red skin with dry white flesh; and purple skin, purple flesh. Just like with other vegetable varieties, each of the color combos has a slightly different texture and flavor.
White sweet potatoes have a less sweet flavor and are often referred to as having a nutty flavor. They are great as side dishes or in hash. The purple-fleshed sweet potato has a more moderate sweetness than the common orange one.
So, if all this has been about sweet potatoes, what about the yam? And why can you still go to the grocery store and at least in the canned vegetable aisle still find canned yams, that look like sweet potatoes, and they are! The answer is interesting.
First, yams are a totally different vegetable. Besides being from a separate plant family all together, they are structurally different, too. Yams look like bark-covered logs with a rough surface, and have a starchy and dry texture.
Where a sweet potato tops out at 5 to 7 ounces, yams can grow up to 7 feet long and up to 100 pounds.
It used to be that you would never see yams in the produce section of most grocery stores unless you were in a specialty market that carry Caribbean, African or Asian produce. I was slightly alarmed to learn that yams are mildly toxic if not cooked. They are a starchy vegetable and usually prepared into a paste (like whipped white potatoes) although they can be fried, baked or roasted as well.
Now that most big box grocery chains have started carrying produce with a more international flair, I have occasionally seen true yams for sale.
So how did these two very different vegetables become synonymous in America? Geography, history and marketing all factor into the answers. The sweet potato originated in the tropical Americas near the Yucatan peninsula. Sweet potatoes have been cultivated for over 5,000 years. The yam originated from West Africa where they have been cultivated for 11,000 years.
According to the Library of Congress, the slaves started calling sweet potatoes “nyami,” meaning “to eat,” eventually anglicized to yams because they resembled the yam (a fleshy tuber) that they had known in Africa.
Further confusing the story, in the 1930s, Julian C. Miller at the Louisiana State University Agricultural Center developed a larger, sweeter, orange sweet potato. They wanted to differentiate their sweet potatoes that were orange and softer than those grown in other states, so they started a marketing campaign calling them Louisiana yams.
To avoid confusion, (which really adds more!) the USDA requires that sweet potatoes are labelled yams, even though they aren’t the same plant family, plant part or culinarily used the same way.
Go figure.