I've wintered mine over for several years. I cut it back almost to the soil level and keep it in an unheated greenhouse over the winter. I water it sparingly, maybe 1x/mo, just enough to keep the roots from drying out. I put it outside and begin watering and fertilizing when it starts to warm up.

Thank you Karyn1. I'll try it. And I'm wondering what zone your in...

I received 6 seeds in a trade and they all sprouted.
I sniped a small cut near the end with toenail clippers and soaked for about 24 hours.
I also overwintered 2 small ones that I bought last year by
doing pretty much the same way as Karen. I did bring them in the house when our weather stayed extremely cold for a few days.
I don't have a greenhouse, but we cover a canopy each winter and put a heater in for freezing temps.
I don't have flowers yet but my vines are about 16' now.

I grew 3 vigna caracalla or snail vines for the first year started from seeds outside. I left one outside with no protection, Used a upside down pot to cover one of them outside and brought a third vine inside still in the gallon pot. The one I brought inside stuck in the back bedroom next to a window went dormant and I kept it moist but not soggy and the foliage stayed alive but was small and slow growing then after I took it outside in the spring it grew like nothing had happened and is doing very well.

The unprotected vine died but the one I protected with a upside down pot lived to grow again and it is doing good too. I live in zone 8b I hope that helps.Karen