I also wanted to mention that my father grew dahlias as well. As a teenager, I remember that he would drag me out to the garden to show me his beautiful dahlias. We lived in Blue Island, Illinois (just south of Chicago). At the time, I was not at all interested:)
At any rate, he would dig up his dahlias and put the entire root ball in the crawl space under the house. I have used this method, but it is not very practical if you have a large number of dahlias. Takes up too much room.
