In past years I have overwintered the dahlias in a plastic container or bag filled with wood shavings . The large roots are usually fine but I lose a lot of the little ones. New ones are usually too small to make it until spring, which is always a great disappointment! Last fall I had some little pieces and small, new dahlias that I didn't want to lose so I potted them up to grow indoors for the winter. 
I kept them as houseplants, sort of, in front of the south patio door. It gets as much light as is possible to get anywhere indoors, as it faces south and has no overhang. My kitchen is also freezing in the winter, which helps.
They sprouted and grew in the pots. They didn't grow fast, but they did grow and are picking up more now that spring is here with longer days and stronger light. I had no problems with them indoors in the winter at all! No bugs, no rot, nothing. I kept them on the dry side and, like I said, rather cold. I'm very pleased with the result!
I will be "storing" my small dahlias and little pieces like this through the winter from now on!
I love my 'Keri Blue' dahlia! Last fall I added a red one with yellow centers and tips and also a dark, rich purple dahlia with white tips. I am looking forward to getting huge blooms from them this year!
They make great cut flowers!
