Once the foliage has been hit by frost, I cut the stalks back to about 6-10 inches above the ground, and CAREFULLY dig the underlying tubers up. They need to "cure" before being stored, so brush off the soil or even easier wash the tubers carefully, then leave them somewhere dry and warm (like 60 degrees or so and airy) to dry for two or three weeks. Then into storage they go: somewhere that’s dry but not too dry (so they neither rot nor shrivel) and that stays about 40-50 all winter. Crawl spaces, unheated but above-freezing basements, etc. Pots filled w/peat moss or bark chips would be good as containers, or boxes with the same material. Check them about once a month to make sure nobody’s shriveling or decaying. If the tubers seem shrunken, they can sometimes be revived with a little misting (NOT soaking). Each year you’ll have more…and bigger ones, too. This is the same basic idea for cannas and dahlias and such in our cold zones.