Certified GKH Gardening Expert
Since they are young, I wouldn't leave them outside. You can overwinter them inside a garage or basement, or where it doesn't get much lower than freezing. Only water them about once a month. Too much water will cause rot.
Another option would be to plant them in the ground and when the tops die back after a frost, cover the whole plant with a few inches of mulch. Uncover them in spring when new growth begins.