Tammy, I
plant onion
seeds in the fall as well as sets of
potato onions to overwinter. If you
plant your I'm not sure about vidalias, but Walla Wallas are fairly hardy. I use row covers over my overwintering onions, but try planting next to the south side of a building for extra protection. You're climate is warmer than mine anyhow, so there's a good chance it will survive.
Also, onions are biennials and need the cold temperatures of winter and then the warming temperatures of
spring and summer to tell them it's time to
flower and set
seed. It also works to store the bulbs in a cool place and replant in
spring, but since yours is already sprouted, it's probably best to
plant outside.