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How to Overwinter Ornemental Sweet Potatoes

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Ornamental sweet potatoes come in a wide range of leaf shapes and colors. Photo: sprinthorticulture.com

The sweet potato (Ipomoea batatas) may be best known for its delicious tubers, but it has also given rise to many ornamental varieties grown for their colorful foliage. You may even have one in your own container garden without knowing it. It is, by nature, a creeping plant, and can be used as a summer groundcover, but it’s most popular as a trailing plant for containers and hanging baskets, as the stems drip gracefully downward when it’s grown in a pot.

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Compare the cut leaves of this cultivar with the heart-shaped leaves of the plants above: there is a wide variety of leaf types. Photo: Krzysztof Ziarnek, Wikimedia Commons

There is a wide variety of cultivars with leaves in varying shades of chartreuse, orange, pink and purple and some are bicolored. Also, the leaves come in a variety of shapes: heart-shaped, star-shaped or deeply cut. Sometimes, when the summer is especially hot, ornamental sweet potatoes do produce edible tubers, but, if so, they won’t be as tasty, as large or productive as commercially grown sweet potato varieties.

Although the ornamental sweet potato is sold as an annual, it’s actually a tropical perennial and that means it’s possible to keep alive over the winter. Only gardeners living in the tropics, hardiness zones 9 to 12, can consider growing it outdoors all year though. Most of us will have to grow it indoors, as a houseplant.

Here’s how:

Easy to Root

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Cuttings of sweet potato illusion® Garnet Lace. Photo: Proven Winners.

In the fall, before nights become too cool (sweet potatoes are very intolerant of cold!), harvest a few stem cuttings about 6 to 10 inches (15 to 25 cm) long. Rinse them well under a tap to get rid of any insects that may be hiding there. Now, remove the lowest leaves on the stem to uncover a length of bare stem about 3 to 4 inches (7 to 10 cm) long. You now have two choices: you can your cuttings in water or in potting soil.

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Rooted cuttings of ornamental sweet potato in water. Photo: apieceofrainbow.com

Rooting cuttings in water is visually very interesting because you’ll see the roots forming. Also, some people do manage to keep them alive in water all winter. Water, though, is not the normal environment for sweet potato roots and the success rate is lower than with the cuttings growing in potting soil. Also, the risk of rot is much greater with plants grown in water. Still, rooting sweet potato cuttings is certainly easy enough. Just insert the lower end of the cutting into a large glass of water or other transparent container and add water whenever the level begins to drop.

Cuttings made in potting mix give more robust plants. Simply fill a pot that has one or more drainage holes (no need for a “drainage layer” of gravel on the bottom), make a hole in the mix with a pencil and slip the lower part of the stem into the hole that so that at least one node (point where a leaf was once attached) is covered. There is no need to apply a rooting hormone. Firm the mix down a bit, then water well. Mother Nature will take care of the rest!

Of course, there is a third possibility: that of starting the cuttings in water, then, when you see the first roots, potting them up. Don’t wait too long, though! When the roots are too long, the plant will have a harder time adapting to a terrestrial environment.

Care Over Winter

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Sweet potatoes make attractive temporary houseplants. The one above is ‘Margarita’. Photo: Proven Winners

The sweet potato loves warmth and sunshine. It will need a sunny window and, above all, one where it never becomes very cool. Ideally, you should maintain a temperature of at least 68˚F (20˚C) while roots are forming. However, it can tolerate night temperatures down to 50˚F (10˚C) once it is rooted. But that’s “tolerate”. You’ll find that sweet potatoes do best when temperatures remain above 68˚F (20˚C) at all times.

If you don’t have enough sun, you can also grow your sweet potato under fluorescent or LED lights. That will ensure more constant lighting and steadier temperatures, much to the delight of this highly tropical plant.

During the fall and winter, keep the glass filled with water (water-grown cuttings) or the potting mix at least slightly moist (soil-grown cuttings). Pinching the ends of the stems occasionally to stimulate branching will help stimulate a more attractive appearance. Good air humidity is also welcome.

It’s best not to fertilize your cuttings right after bringing them indoors. Under the short days of fall and winter, you’ll want your plants to grow slowly. Excess growth at that season will tend to be stretchy (etiolated) and unattractive. By winter’s end, though, that is from late February to mid-March on, days will be long enough that you’ll want to stimulate growth again. From then on, apply a fertilizer according to the instructions on the label. The sweet potato is not at all picky about the fertilizer’s formulation, so just use the fertilizer of your choice.

When Spring Has Sprung

Simply keep up the same care in the spring as you did all winter: watering, fertilizing, pinching, etc. But it’s also the season to “take cuttings of your cuttings” if you need more plants for your summer container gardens. This time, though, do root them in potting mix. Plants rooted in water will not acclimatize well to planting outdoors.

When outdoor temperatures warm up, gradually acclimatize (harden off) the plants to outdoor conditions, especially the sun’s ultraviolet rays. Remember that the sweet potato is very tropical: do not try to move it outdoors permanently until night temperatures regularly rise to more than 50˚F (10˚C). Depending on your local climate, that might well not be before the end of May or even in June.

Flowers?

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Blooms on an ornamental sweet potato. Photo: MSU Extension Service/Gary Bachman

Sweet potato rarely bloom at the best of times and ornamental varieties are even less likely to bloom than agricultural varieties. However, if the summer is long and hot, some cultivars occasionally produce a few pink to purple trumpets with a darker eye. If you think they look a lot like morning glories (Ipomoea nil and others), you’re correct. Both plants belong to the genus Ipomoea.

All that’s left is to let your ornamental sweet potato decorate your container gardens and hanging baskets in either sun or partial shade for the rest of the summer. Then, in the fall, bring in a few cuttings and start the cycle anew.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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