Here is the FAQ entry on ways to do this

I have two small refrigerators that I keep at 45 - 50 degrees just for over-wintering crocosmia corms and dahlia tubers -- would this be bad for canna rhizomes?

I washed them, let them dry, sprayed with lime sulfur, and sprayed the spindly ones with anti-dessicant, put them in paper bags filled with peat moss, labelled the bags, and put the bags in a box packed with newspaper, and put the box next to the heated wall of the house because the garage freezes sometimes. They came through very well, no losses.

I received dozens of plants from my neighbor last fall and the year before I dug up several of mine to thin the beds. After cutting the greens off, I knocked off most of the dirt and set them in cardboard boxes making sure the dirt was dry first.I closed the lids so they wouldn't get light and this spring I took them out and they all had new shoots starting out. I stuck the boxes under a large work table in an insulated side room of the garage. I had a small heater that I turned on only if it would get freezing in the room which it seldom does. I gave a lot away to friends and they all had success growing them.

50 would be too cold.

Thanks so much! So what temp would be too WARM?