Re: Musa velutina hardiness.
I started mine off from one gallon containers 4 springs ago, and the clump in my photo gallery is from a one gallon container that I have divided off quite a bit from. I honestly think in your location those one gallon containers are plenty large enough to go ahead and plant out. You know how much faster they grow in the ground versus in a pot and if you are nervous about leaving them out, dig a pup to overwinter and see what happens. Hey, just a suggestion.... Best of luck with whatever you decide to do...