How do I store canna rhizomes that can't be planted till next spring?

Make sure there is no soil on the tubers. Place them in a brown paper bag with sawdust. Keep in a cool dark place. The sawdust will prevent moisture so they do not rot. Rhizomes, tubers, and bulbs should be stored this way.

Dark shady dry place

When you store them by William’s technique, make sure any growing stem from this year is tipped down, then if there is any remaining moisture it drains away and that diminishes rot. I just stick them in an oversized box in the coolest part of the cellar and skip the shavings, but the correct method is the sawdust....