Dahlias are not winter hardy and do need to be dug over the winter months. The Turmeric roots may fall into a similar vein, although horseradish as a root is very hardy. You may want to just plant some in a big container and move into a warmer ( cellar) area for the winter. Try planting a few directly into the garden and save a few for a container. In this way, you will know what survives and what doesn't, then take it from there.

The only gardening book that I recall ever seeing turmeric (Curcuma domestica)in is the Hawaiian Organic Growing Guide (by Shunyam Nirav), written (naturally) for Hawaii (where the plant is called 'Olena). The Complete Book of Herbs and Spices (by Sarah Garland) says "turmeric is a tropical plant cultivated in China, India, Java, and Peru."

I believe that the very definition of a tropical plant is one that doesn't have the sense to go dormant for winter, which is why in Zone 5 they are either grown as annuals (e.g., tomatoes) or grown as houseplants. However, the Hawaiian Guide confuses the issue (and me along with it) by saying, "the leaf stalks come up in spring, the yellow and white flowers bloom, then the plant dies down in the fall."

This leaves me agreeing with ksrogers, assuming that you have more than one plant, or a big enough plant to divide. If you have only the one, I'd try it in a pot. Regarding the plant's culture, the Hawaiian Guide says only that it "needs sufficient moisture [which may imply that misting or setting the pot on a water-filled tray of pebbles would be needed to keep the plant healthy indoors in dry winter air], and prefers rich soil and some shade."

Most of the Tropical plants can not stand Freezing temperatures. That is why, I believe ,ksrogers suggestion makes good sense to plant few tubers in pots and bring them indoor during winter time.

You need to protect the turmeric from the cold, but you might want to wait until it is ready for harvest until you store rhizomes. I am going to try & overwinter mine, unless the leaves wither. The best information I have found on turmeric is turmericworld.com.

They dry the rhizomes & store them in underground pits. Here is a link:

http://www.turmericworld.com/turmeric-curing.htm

You might also read the harvesting link.

The rhizomes can dry up if kept too dry or rot if kept too moist. They need to be somewhat hydrated, so you can break dormancy with your next crop.