This year I grew the two most common varieties of ornamental sweet potato vine; Ipomoea batatas "Blackie" (black sweet potato vine) and "Marguerite" (green leafed variety) in containers in my garden. I grew a black sweet potato vine in my small container alongside my black Calla Lily and a black Oxalis (you can search my blog for photos) and two more in a large container with Coleus "Kong". The only sweet potato vine that flowered and produced seeds was the sweet potato vine that was in the small pot with the Calla Lily and black Oxalis.
My theory on my sweet potato vine flower.
I'm no expert but I wonder if crowded roots, poor soil quality and drier growing conditions lead to the flowering, fruiting and seed production in the sweet potato vine. The soil makeup of smaller pot was also poorer quality than the larger pot and would often dry out once the plants all were established. Perhaps this lead to stress in the plant and that stress triggered the flower and seeds production so it could reproduce before it died. The plants in the larger pots that had ample room to grow and never dried out concentrated in growing foliage. I've seen sweet potato vines in planters around Chicago for year and never noticed the flowers. When mine began to flower I paid extra attention to the public planters to see if they would also flower but I never observed a single flower on them.
Sweet potato vine tubers are weird.
When I lifted the sweet potato vine tubers in the photo above I was expecting something that looked more like potatoes-to me they look more like something you'd find inside of a baby's diaper than a potato. The other interesting thing about the tubers that I can't get over is the coloring of the tubers. The reddish tuber came from a black sweet potato vine and the larger lighter tuber came from a green sweet potato vine but the smallest tuber in the picture above also came from a black sweet potato vine. Does the color of a sweet potato vine vary with age of the tuber?
Overwintering sweet potato vine tubers.
After I washed off the tubers I placed them inside of a paper bag where I'll keep them for the winter in a cool and dry area of the house. If I had more room to spare I would have kept them inside the pot and let the foliage die back and allow the soil to dry out and place them in the area where the bare tubers will go. I've been doing some reading and some garden bloggers have reported that the tubers are slow to wake up in the spring and start growing. Maybe storing the tubers isn't such a great idea if you're looking to save some money in the spring. The other thing I noted was some gardeners stating that the tubers they left potted and stored were prone to rotting compared with those stored bare.
Some history for the garden nerds.
I did a search on Google for Gardeners looking for storage information and came across an interesting article on sweet potatoes. Here's an excerpt;
Sweet potato was already an important crop on Pacific islands when Europeans landed on the islands: Easter Island (Roggeveen, 1722), New Zealand (Cook, 1769), and the Hawaiian Islands (Cook, 1778). Sweet potato, known as kumara, was a staple in the diet of the Maoris of New Zealand; interestingly, the name kumar is used for this plant in Peru! Rongo ma-Tane, a Maori god, protects this plant; a buried tuber is powerful enough to cause enemy to go mad and run away.
Given that the species does not generally reproduce from seed, the spread of this plant must have been by the transport of the root tubers. Therefore, the pre-Columbian occurrence of sweet potato in southern and eastern Polynesia, as well as in New Zealand, needs an explanation. Certainly the plant originated in the Americas and was carried westward into areas where Asian root crops had not yet arrived. Two equally plausible hypotheses have been proposed: (1) Polynesians raided the Peruvian coastline and took sweet potatoes back with them; or (2) early Peruvians, who used balsa rafts, transported sweet potatoes to Polynesia on their oceanic forays (as tested by Thor Heyerdahl's Kon-Tiki experiment in 1947). Long-distance dispersal by ocean currents has been ruled out, because the tubers spoil in seawater.... Source: "Batatas, Not Potatoes".
Edit: see the new post on ornamental sweet potato vine propagation for a picture of sweet potato vine seeds and how to take cuttings of ornamental sweet potato vine. The post also explains if ornamental sweet potato vines are edible.