For our climate, it's recommended that you dig up your dahlias in the fall and store them in a paper bag in the basement over the winter. Then replant them in the spring. You should let the stalk die off naturally allow the tubers to sit out in the sun for a few days.
This is my big salad plate dahlia. The tubers have really multiplied and grown! You can break these up and each one will have a flower next year.
I separated the different colored dahlias, so I would know which was which next year.