I am certainly no expert but I have found that cannas do best when stored with the soil around the rhizomes. I just dig them up after frost has blackened the foliage, cut off the foliage and leave them to dry up a bit for a few days. Then i just wrap them loosely in newspaper and store in boxes in the basement or just dump them in a plastic garbage bag (not sealed). In the spring you can divide them and pot them up. I wouldn't worry too much about your stalks being a bit moldy as long as the rhizomes are still firm. I would cut off the mouldy stalks and store the rhizomes in very slightly moist peatmoss. Don't cover with plastic, that just encourages rot. Good luck.

Well, I cut off the moldy parts a few weeks back. As of last night, I still had soft and moldy rhizomes! 8-(

Looks like I will have to get new ones come spring time.

the problem is that you waited too long to dig out the rhizomes. i suggest you don't wait until after a freeze. why take a chance? cold + wet = not good! The mold could have infiltrated before you cleaned and dried them.

dig out your plants before they are damaged by frost and trim off what you need to.

also, caladium i think have a greater tendency to develop molds, maybe being in close proximity to them, it spread???

Another cause of moldy cannas can be from storing them at too cold of temperatures. They prefer 50-55 degree temperatures in storage. Colder temperatures, especially near freezing, can cause mold and death to cannas.