At the Nursery we are on very sandy soil so it is free draining so we are able to leave the tubers in over the winter period. After the Dahlia foliage has gone black and horrible wait a couple of weeks for the sugars to go back into the tuber then cut the stems off just BELOW the soil level then mound the soil up over the crown like a mole hill.
Unfortunately if your Dahlias are in Clay or wet soil you will have to lift your Dahlias after the frost has hit them. After the first frost and they have gone black and horrible wait a couple of weeks for the sugars to go back into the tuber then dig out the tuber make sure that you thoroughly washed off and dried so that their isn't any moisture on the tuber. Then store somewhere Frost and Damp free.
Alot of people relate Dahlias with Earwigs so if you do have a case of Earwigs where the flower petals have been nibbled all the way round, then to remove them place a cane next to the plant with a pot stuffed with newspaper then at night the Earwig will go up and read the newspaper and you will be able to dispose of them appropiatley the next morning (Not to your neighbours dahlias!)