Monday, October 31, 2011

Sweet Potato - Ipomoea batatas

Ornamental Sweetpotato, Ipomoea batatas 'Marguerite'
The news column this week has a segment about harvesting, curing, and storing sweet potatoes (Ipomoea batatas - part of the morning glory family), whether they’re the ones we grow for food, or the ones we grow for show. Believe it or not, given my preferences for growing edibles, I’m more familiar with growing the ornamental ones than the edible ones. I added ‘Tricolor’ this year to the chartreuse ‘Marguerite’ and dark ‘Blackie’ cultivars I've grown in the past as spillers in my container arrangements. I’ve also seen them grown as sprawling ground covers, spreading over a bank in home landscapes. Each year, new cultivars of the ornamental ones arrive with different colored leaves or shapes.


Ornamental Sweetpotato Ipomoea batatas 'Blackie'
You probably noticed a few of them in the containers around the Extension Office this year. New varieties trialed this year at Landisville (scroll down to the Ipomoea pictures at the link) include two from the ‘Sweet Caroline’ series developed by North Carolina State University: ‘Bewitched Improved’ and ‘Raven’. Check out the ‘Sweetheart Red’ and ‘Sweet Caroline Red’, ‘…Bronze’, and ‘…Light Green’ trialed by Cornell in Ithaca, NY. There are 14 varieties from the ‘Sweet Caroline’ series alone.
It's not only the color but the leaf shape and plant habit that makes the Sweet Caroline series so popular. And we've gotten more creative with the names -- "Bewitched" and the Sweet Caroline Sweetheart color series have followed the 2002 releases. The border series is next, and there are flowering and several variegated varieties in the pipeline.

The twist to this particular story is that the breeding program went against the conventional wisdom that you don't bring in "wild" varieties.

"They're part of the morning glory family," Yencho said. "And the morning glory is a prolific bloomer. What we've done is selectively breed a wide range of sweet potato varieties and then we selected them in such a way as to produce a great variation in color and shape of the leaf. So, in this project we were more interested in developing pretty foliage, not pretty storage roots, which is what people typically think of when they think of sweet potatoes.

 "Typically, what happens is that when you breed plants you don't bring in less adapted varieties, unless you really need them because they tend to cause the whole thing to collapse. Just the opposite has happened with ornamental sweet potato vines. The wild varieties have given us the range and the beauty of the plant that we see in the Sweet Caroline series. And, we've been able to take some of the lessons learned on the ornamental side over to the food-crop varieties."
Compared with the food-crop varieties, the ornamental ones are pretty expensive. Donna paid about $9 or $10 for 25 slips for the Victory Garden this year, while I paid about $2.50 for each one for my containers, about 6 times as much per plant. Still not very much, since I only planted four, but since becoming a Master Gardener, I’ve become more and more curious about the science of Horticulture and propagation methods. Plus I'm cheap (tho' I prefer the word "thrifty").

Ornamental Sweetpotato 'Tricolor'
I even tried, unsuccessfully, last year to produce a tomato/potato graft, just to see if I could do it. Took pictures and everything, anticipating a blog post on the subject.  It didn’t work out too well, probably because of the heat and drought of last year (that’s my story and I’m sticking to it) but I’m sure I'll try again in the future. Just 'cuz. At any rate, I’ve also been unsuccessful saving the roots of the ornamental sweet potatoes for propagating the following spring. Probably because I didn’t cure them properly, and I stored them with the dahlias, glads, and cannas, which have different humidity requirements while in storage.

Rescued Roots, Curing
So, I’m going to try again this year. Here are the ones I rescued from the compost bins at the Extension Office, my containers, and one food variety saved from the Victory Garden class. They’ve been cured, individually wrapped in newspaper, and are now stored in my basement. Come March, I’ll try to revive them and create my own slips. Any extras will be offered for the plant sale (assuming I’m successful). It’s not too late for you to give it a try, even after all that early snow we got this weekend, but you better do it now, since storage ability can be affected if exposed too long at temperatures below 50 degrees. Dig in the earth or container, looking for the large, fleshy roots. Cure them at 85 – 90 degrees for 10 days, or 70 – 75 degrees for 2 or 3 weeks. Wrap in newspaper and store in a cool (55-60 degrees), dark place, like an unheated basement, or closet.

By the way, I used to think they were tubers, like white potatoes, but they’re not. Tubers are fleshy storage underground stems. Sweet potatoes are fleshy storage underground roots. Here’s a good fact sheet explaining the differences among the various underground plant storage mechanisms – bulb, corm, tuber, rhizome, fleshy root, etc.

A final note. Sweet potatoes are not yams. Yams (Dioscorea spp.) are a different genus and species altogether (see fact sheets here and here), and are rarely, if ever, sold for food in the U.S., and we probably wouldn’t like them, if they were. They are a major nutrient source for people in Africa, however. The orange sweet potato that is a staple for Thanksgiving is commonly, but mistakenly called a yam (although if you look closely, you’ll notice that the word ‘sweet potato’ is somewhere on the labeling package, per USDA regulation).

The term  "Yam" was introduced to differentiate a new variety of sweet potato that was orange-fleshed, and moister when cooked than the then standard white and comparatively drier variety. It’s purely a very successful marketing ploy to rebrand a product. So when you watch a cooking show, or follow a recipe that calls for yams but goes on to say that sweet potatoes can be substituted if you can’t find yams, you can now smile knowingly.

UPDATE: 11/2/11 - The University of Georgia trialed several ornamental varieties in 2011.  Start here and see the results for 16 different cultivars.

UPDATE 2:  11/3/11 - Some nutritional information and sweet potato recipes from the Washington Post.

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