Dahlias?

When you lift the tubers cut the stems down to 4 to 6 inches, wash off any soil then push a knitting needle down the stem then turn them upsidedown doing this helps let any water drain out from the tubers, once dry store them in dry soil or compost, they must be kept frost free, if in future if leaving them in the ground over winter you can take cuttings from the new shoots just as normal