Growing and Propagating Ornamental Sweet Potatoes: Save them for next year and save $$
Check out the listings in PlantFiles, or start looking around garden centers this spring, and you'll be amazed at the different varieties of ornamental sweet potatoes. They can provide either complementary or contrasting color in containers, adding the third element to the design trio of "thriller, filler, and spiller."
The deep purple leaves of 'Blackie' contrast beautifully against bright green foliage and work with nearly any flower color. For an elegant look, pair it with lavender 'Tidal Wave' petunias! 'Tricolor' has green leaves streaked with pink and cream, and I love it with pink or purple flowers. Last year, it contributed to a riot of color and texture in a railing planter on my deck, working especially well with a magenta ivy-leafed geranium. 'Marguerite' is a popular lime-green variety that punches up container color and would be a great accent in a coleus planting.
Other varieties add different textures and colors to your containers also. or 'Ace of Spades' has the same color as ‘Blackie' with a simpler leaf shape. The finely dissected leaves of 'Lady Fingers' have a lacy look that would soften the edges of a container planting. You might even consider using the broader green foliage of a garden-variety sweet potato to anchor a design that needs a bold spiller.
These fancy-looking plants do come with fancy price tags. Here, they are usually sold in 4-inch pots for at least $5 per plant. At that price, I can only afford a few. Even if I could only grow them for one season, they add so much to a container that I'd probably still splurge on a couple. But I can feel smug when I splurge, knowing that one $5 plant can turn into dozens over the years.
As a kid, I remember taking a chunk of sweet potato and inserting toothpicks to suspend it over a glass of water. I watched in fascination as it sprouted first roots and then luxurious green foliage that scrambled right over the edge of the counter. Propagating ornamental varieties is just as easy!
In fall, before your first freeze, you'll need to "lift" your ornamental sweet potatoes and bring them inside for storage. Dig around underneath the plant and pull up any tubers you find. Some plants may make one large tuber, others may have formed a number of smaller, oddly shaped potatoes. Even the smallest tuber can give you new plants for next year, so feel around carefully and get them all. If an unexpected freeze kills the plant, don't give up on the tubers - they are likely just fine, under their blanket of soil.
Rinse and dry your treasure trove of rescued tubers, and store them in a cool, dark, dry place (I use my canning cupboard) until you're ready for them. They're perfectly edible and reportedly tasty when roasted, but I'd rather grow mine than eat them. I like to start slips from the tubers at least 8 weeks before my planting-out date (a couple of weeks after the average last frost date).
Start them the same way you sprouted sweet potatoes as a child, over a glass or dish of water. A small part of the tuber should be touching the water, to encourage roots to grow, but if you stick it too far into the water you may have trouble with rot. Change the water every day or two. Once roots begin to sprout, only the roots need to be in the water, and the tuber can be safely dry. Ornamental sweet potatoes are very forgiving. If you goof and let the roots dry up, just put the tuber in a fresh glass of water and it'll start growing again.
Little nubs will soon appear on the top part of the potato. It's fun to watch them unfold tiny leaves and start stretching into sweet potato vines! When the sprouts (also called slips) start getting their second or third pair of leaves and are big enough to handle easily, just snap them off at their base. Pot them in barely moist soil-less potting mix. I often put 3 slips into a 4-inch pot, but single slips will fit nicely into a 2-inch pot or a small cup with a couple holes punched in the bottom.
Because the slips don't have roots yet to take up water, extra humidity can help keep their leaves crisp. You can make an easy "humidity dome" by popping a plastic bag over your cuttings. Use chopsticks or something similar in the pots to hold the plastic away from the leaves. Leave the bag loose at the bottom or snip a couple of holes in it for ventilation.
A bit of moisture is good, but don't drench the potting mix with water until roots develop, or your cuttings may rot. Water as needed to keep the soil moist but not soggy. Bottom watering (putting your pots in a tray or pan with a quarter to half an inch of water and letting them soak it up) will help prevent fungus gnat and mold issues.
Stand back and watch them grow! When they've put out a few inches of new growth, either pinch the tips or take cuttings. The vines will branch below where you've pinched, and cuttings can be rooted in water for still more plants. If your little plants start getting root-bound before planting-out time, you may want to up-pot them.
So go ahead and splurge on a couple of different ornamental sweet potatoes for your patio containers this year. Enjoy their cascades of wonderful color and texture. And plan how you will incorporate dozens of these beauties into next year's containers, by saving and propagating the tubers!
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Photos by Jill M. Nicolaus
For more information about "regular" sweet potatoes, check out these DG articles:
Sweet Potatoes or Yams: Which is Which? by Lois Tilton