Canna Indica overwinter problem

[Fab]

Hello everyone! I have a problem with my Canna Indica.
It is the first year that I have these flowers and therefore it is my first winter handling the rhizomes.
On the advice of my florist, after cutting the plants in fall, I left the rhizomes in the pots with soil, I placed in an unheated room and covered them, so that they could stay in the dark.
Problem: i saw that new plants have grown anyways!
I thought the problem was an insufficient coverage. So I cut the plants back and added more cover, but they are growing again even under the cover.
I guess the problem wasn't the light, but that the room is probably too warm?

Well now I don't know what to do, is it too early to remove the cover and let them grow (indoors until winter is over)?

 

[Logan]

Cut them down and put them somewhere very cool but frost free.

 

[Marck]

Greetings, welcome to the Forums.

I have personally witnessed Canna cultivars in the Midwest (USDA Zone 6: down to -10º F/-23º C), that were left in the ground over Winter and reliably returned year after year. The beds were mulched in Fall, but no other protection was given. Most articles say Canna are only hardy to Zone 7, but clearly, this is not always true. I don't know the cultivar identities of those cold-hardy Canna.