The somber blooms of Ipomoea batatas 'Blackie' wowed me when it bloomed in my garden a couple of years ago. I was already a fan of the dark foliage, but the beautiful flowers made me see this ubiquitous annual in a whole new light. Out of curiosity I pollinated the blooms by inserting a paintbrush in the center of several flowers. Some of the literature online I came across at the time explained that either ornamental sweet potato vine didn't produce seeds, the flowers were sterile or that plants wouldn't come true from seed. Undaunted and up for a garden challenge I continued hand-pollinating the flowers.
The sweet potato vines rewarded me by setting several seed pods that matured and produced seeds. If the seeds and seed pods are evocative of morning glories that's because they're both related. Sweet potato vine seeds are small, brown and very hard, like seeds from other Ipomoeas. I don't think seeds from a cultivars like 'Black Heart', 'Blackie', 'Tricolor' and 'Marguerite' will produce plants that are true, but it will be interesting to germinate the seeds anyway. There is also the possibility that the seeds themselves are sterile and will not germinate.
A far easier way to propagate ornamental sweet potato vines is to take cuttings. Vegetative propagation of ornamental sweet potato vines is really the only way to assure that your plant will look like the plant you want to make more of.
Ornamental Sweet Potato Vine Propagation by Cuttings
Step #1: Take a cutting from a sweet potato vine that is at least four inches long. Really long sweet potato vines could be cut in half.
Step #2: Remove all the leaves on the vine leaving only a couple at the tip so the cutting can complete photosynthesis. The lower leaves will likely die on their own if you don't remove them because there aren't any roots to feed them, but just remove them anyway to avoid having to pick them up from your potting area, kitchen sink or windowsill later.
Step #3: You can place your cuttings in potting soil or water. I like to put my ornamental sweet potato vine cuttings in water because they seem to root faster and I can observe the root growth. Place the cutting in a warm and bright place out of direct sunlight. Make sure that most, if not all, of the leaf node are submerged in water. Roots will start to form along the "bumps" at the leaf node.
After about a week you should start to see the formation of roots along the leaf nodes on your sweet potato vine cutting. Transplant your cutting into a pot once you have a nice bunch of roots forming along the leaf nodes that were under water.
Propagating your ornamental sweet potato vines is really easy and you don't need any special rooting powders or liquids to do so. Within a couple of days you've created a backup that you can overwinter indoors and plant in your garden next year. I should note here that most ornamental sweet potato vines are patented and by propagating them you're breaking the law.
If your sweet potato vine is already potted you can bring it indoors and treat it as a houseplant. The tubers of ornamental sweet potatoes can also be lifted, cleaned off and stored indoors in a cool and dry location in your home and planted out in the garden again in the spring.
Are Ornamental Sweet Potato Vines Edible?
Ornamental sweet potato vines are bred for their foliage, which is why they're described as "ornamental." All of the work in their breeding went into producing beautiful foliage or plants that grow well in poor garden conditions. If you look at the link above 'Blackie' didn't produce tubers that were very large, which would make it a poor choice for a sweet potato you want to eat. Varieties like 'Marguerite' may produce sweet potato tubers that are much larger. So, yes, ornamental sweet potato vine tubers are edible. Whether they are palatable is another question, one which I can't answer. Through the magic of the internet I witnessed saw Chef Jackson, who blogs at The Pleasant House, forage ornamental sweet potatoes from a sidewalk planting in Chicago and cook them. Do with that information what you will, I for one would not eat an ornamental sweet potato vine. Not because I'm above eating them, but because you don't know what chemicals were used in their production at nurseries.