When should I dig up my Dahlias and how do I store them?

Before frost,clean and store in a paper bag in a cool dark location

Here's another article that will give you some insight into digging up dahlias for winter storage. I hope it helps you!

They are bit winter hardy. Prior to frost, dig them up. Place in something that air can circulate, like an old onion bag or old basket. Place in cool dark place that does not get below freezing, like a garage or basement. Pull out in spring and replant.