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LIFE GARDEN difference between sweet potatoes and yams how to grow and cure sweet potatoes southern exposure seed exchange
difference between sweet potatoes and yams how to grow and cure sweet potatoes southern exposure seed exchange

Sweet Potatoes or Yams?

by Mary Jasch

Where have all the sweet potatoes gone? There seemed to be a dearth of them this autumn, winter and spring with a coincidental explosion of yams. This year, signs on supermarket bins filled with the common large, red-skinned, orange-fleshed spuds proclaimed “yams” for sale. Once in a while, they were labeled “sweet potatoes,” but I have grown to know them as yams! To make matters worse, signs saying “yams” often hung above boxes labeled “Southern Sweet Potatoes” that came straight from the growers!

Confusion raged in my search for a real sweet potato and I determined to get to the bottom of this: why is the same vegetable labeled as two different ones; what, exactly is a yam and what is a sweet potato; and why the confusion!

Ira Wallace, Co-manager at Southern Exposure Seed Exchange in Mineral, Virginia, set me straight. Ira’s job in this co-op farm and seed catalog business is working with variety selections, including the 15 varieties of sweet potatoes the farm grows and sells, and writing catalog captions. Plus, she is author of the book, Guide to Vegetable Gardening in the Southeast (Timber Press 2014).

There are no true yams sold in the U.S. except in Asian and African markets, she said. “Definitely when you have one you think ‘Oh, aha!” Yams are white with scaly skin, low in beta-carotene and toxic until cooked. They can also grow as long as a person is tall and weigh 100 pounds. Plus, they are a different species entirely and even different families in the botanical hierarchy.

The truth turns out to be: Yam family: Dioscoreaceae, (Dioscorea spp.) Sweet Potato or morning glory family: Convolvulaceae, (Ipomoea batatas)

Ms. Wallace said that the variety ‘Beauregard,’ with deep orange flesh has been an old standard in U.S. markets for 40 to 50 years. It can get quite large and cooks up sweet, tender and moist even when baked in the skin. The skin on all sweet potatoes caramelizes when baked and is quite a low-carb, sweet treat. A smaller variety, ‘Covington,’ a Beauregard look-alike, keeps a smaller size desired by today’s smaller families.

‘Carolina Ruby’ is medium sized with beautiful color – dark orange flesh and ruby red skin – that bakes in a half-hour with “nice caramelized action.”

“We like to use whites in soups and stews because they aren’t quite as sweet. They’re half way between squash and white potatoes in terms of texture and taste,” said Wallace. “They break down and thicken the pot.”

You will “eat your vitamins” with ‘All Purple Sweet Potato,’ a traditional Japanese variety with purple skin and flesh that remains purple when cooked. Its high count of anthocyanins makes it extremely nutritious.

North Carolina grows over 50% of the nation’s sweet potatoes. In 2015, NC growers planted 83,746.16 acres of sweet potatoes – around 817,000 tons of sweet potatoes,” said Lauren Parrish, communications specialist, NC Sweet Potato Growers Commission, Benson, NC

So, relax, sit back and enjoy your sweet potatoes. Know that your candied yams are really candied sweet potatoes.

Ira Wallace's Advice on How to Grow Sweet Potatoes
- Prepare the soil and cover it with black plastic for two weeks before planting to warm the ground.
- If you like, keep the black plastic on and cut a hole every foot, put the slip in and hand water or have drip tape under the plastic.
- Plant slips when the ground temperature reaches 60 degrees (80 degree air temp). Buy a soil thermometer.
- Some people grow the plants in 5 gallon containers – one slip per pot.
- Plant two-thirds of a slip keeping one set of leaves above ground.
- Keep plants watered.
- Once plants start growing they don’t need much attention them except weeding.

Ms. Wallace's Advice on Sprouting Your Own, Harvesting & Curing
How to Grow Your Own Sprouted Sweet Potatoes
Put three or four toothpicks in the sweet potato and emerge halfway in water. Let it sprout. When the sprouts are 6-8” long, cut the potato with attached sprouts and plant when soil is 60 degrees. Get a soil thermometer!

Sweet potatoes grow in a clump right where you plant the slip. If you let the vine ramble on the ground, it’ll root at the nodes and produce smaller sweet potatoes. It’s best to grow them vertically. Expect 4 to 8 pounds per plant with 90 to 100 days till maturity.

When to Harvest Sweet Potatoes
It is critical to plant as soon as the soil reaches 60 degrees. Don’t wait because sweet potatoes take 90 to 100 days till mature – that means all of June, July and August for growing. Harvest in September before the ground starts to cool. They won’t cure right in cold ground and quality will be diminished.

How to Cure Sweet Potatoes
Cure sweet potatoes in a warm space over 80 degrees with high humidity such as a closet with a space heater and bowl of water. If at 90 degrees, cure in one week. If at 80 degrees, cure for two weeks but no longer to prevent drying out. Curing makes them sweeter.

Store at room temperature out of the light to prevent sprouting again. Do not refrigerate. “They are one with the highest nutrients of common storage vegetables,” said Wallace.

To further clean up the spud vs. yam mystery, I asked the produce manager of a large supermarket chain why the store labeled sweet potatoes “yams” despite being displayed in their grower’s box that was clearly labeled “sweet potatoes?”

He said they’re the same thing. I said no, they’re not.
He said the only difference between them is if the inside is smooth it’s a sweet potato and if it’s fibrous it’s a yam. I said that’s not true. They are a different species.
So he said: “Well… if you want to go that deep. I said ?!?
He said people want to buy yams” for candied yams so he has to label them yams. I said but they’re not yams. Yams are tropical and come from Africa.
He said that’s not true….

What ever happened to truth in advertising? Or doesn’t it matter if it pertains to “just botany”?

And the beat goes on….

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published May 04, 2016

Photos to enlarge

Yam or sweet potato? Julian Sparacino photo

Beauregard, Photo courtesy Southern Exposure Seed Exchange

All Purple, Photo courtesy Southern Exposure Seed Exchange

Bradshaw, Photo courtesy Southern Exposure Seed Exchange

Carolina Ruby, Photo courtesy Southern Exposure Seed Exchange

Ginseng, Photo courtesy Southern Exposure Seed Exchange

Hernandez, Photo courtesy Southern Exposure Seed Exchange

O'Henry, Photo courtesy Southern Exposure Seed Exchange

Violetta, Photo courtesy Southern Exposure Seed Exchange

White Hayman, Photo courtesy Southern Exposure Seed Exchange

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