While S. tubiflora is hardy and will take short periods of cold weather (0 F), the operative word is short. If the tuber freezes the plant will die. Fortunately S. tubiflora sends out underground stems that produce new tubers at their ends. Thus if the main tuber freezes, these secondary tubers, hopefully deeper in the ground, will grow again (but late) the following spring. S. leucotricha forms one ever-growing-larger stem tuber. If this is frozen during the winter, you'll be buying another plant the following spring. Well-drained soils also seem to be critical for plant survival in the winter. Jon Fayetteville, AR Zone 6b