There actually are two plants sold under the name corkscrew vine (Vigna caracalla). The one pictured here generally is considered the most desirable, since it sports multi-colored, fragrant flowers, while the other produces solid lavender, less heavily-scented blooms.
Gardeners occasionally like to distinguish between them by calling the second Phaseolus caracalla or snail vine, though botanists don't seem to agree that the two are different plants. Some gardeners think the lavender type actually is Phaseolus giganteous rather than caracalla.
I can’t give you an answer on that, but did grow the multi-colored form this summer—in a pot, since it only is hardy in zones 9 through 12. What I can tell you is that the blooms didn’t appear until late September here in zone 5, and continued until I brought the plant indoors in mid-October. The people at Logee's Greenhouses agree that the heaviest flowering period generally occurs in October and November.
The blooms, which curl like snail or nautilus shells, begin white and violet and age through yellow to tan. As you can see in my banner photo, they always have a few tiny ants scrambling over them. Some sources claim the ants are required for pollination. However, in Tropical Flowering Plants, Kirsten Llamas writes of corkscrew vine flowers that "When a bee lights on the lower petals, a lever-like action forces the stamens to protrude from the coiled floral tube, dusting the bee's head with pollen." (Please don't ask me who's right about that either!)
My plant, growing on an obelisk in a large pot, suffered a bit from yellowing leaves and tiny brown spots on the blooms. I'm not certain whether that could be ascribed to a dry period in late summer, to spider mites possibly instigated by that aridity, or to alkaline conditions caused by my having to water the vine frequently with hard tap water. Since I didn't notice any webbing on the leaves which would indicate mites, I should have tried applying liquid iron, but never got around to that.
I probably will place my vine under grow lights over winter. Being pressed for space though, I have been debating whether I should try digging up the tubers instead. Those reportedly can be stored in the same way you would store dahlia tubers. Keep in mind that a first-year corkscrew vine doesn’t always make tubers, though the folks at Almost Eden note that it is more likely to do so if it was grown from seed rather than from a cutting.
If you want to try starting a vine from the bean-like seeds, pour boiling water over those seeds and allow them to sit in the cooling water for about 24 hours. Then sow them no deeper than 1/2 inch beneath the surface of your seed-sowing mix and keep them warm. Under those conditions, mine sprouted in 8 days, but seeds which don’t have the boiling water treatment—or a chipping and soaking before planting—are likely to take longer to germinate.
The vine prefers well-drained and fertile soil in full sun, and can remain evergreen in frost-free climates. Even there, it tends to die back if temperatures drop below 50 degrees Fahrenheit, which isn’t a problem as it should re-sprout in spring. If you want to prevent the plant's dropping into dormancy, you'd best keep it at above 60 degrees indoors.
To add to the confusion surrounding corkscrew vine, some gardeners have dropped the Vigna genus name completely and now call the plant Cochliasanthus caracalla. Maybe we just can agree that this plant's identity is all corkscrewed up!
The banner image is my own. The pods image is by dave and the vine image by emmaregina1, both from the Dave's Garden PlantFiles. The antique image is from the 1803-1804 The Botanist's Repository by H. C. Andrews, courtesy of plantillustrations.org.