Take time to label each Dahlia: name, color, variety. Carefully dig up dahlia tubersusing a digging fork after the first hard frost in fall (when the leaves turn black). Cut the stalks so they are about 8" tall from the ground.
In mid to late February, unpack your (labeled!) tubers carefully to see which survived and which didn't. Discard any tubers that have dried up like a raisin or those that appear rotten. A healthy tuber should be firm like a potato.
Make up tags with the names of the Dahlias to stick into the pots.
Fill empty, clean grow pots with damp Pro-Mix and and sit the healthy tubers (tuber side down, stem side up) on the soil. Carefully pack more soil around the tubers up to the crown. When finished, store in a dark spot or cover with dry, clean newspaper until you see signs of life!
Once the Dahlias have sprouted, move to a warm, sunny spot inside your house and let them grow. Give them a few splashes of water now and then-- but not much. If over watered, months of work will be in vain.