Dahlias are tender annuals, but you can overwinter them pretty easily. In fall, after the first frost has blackened the foliage, cut off all but 2 to 4 inches of top growth, and carefully dig tubers without damaging them. Allow tubers to dry for a few days in a frost-free location, out of direct sunlight. Once dried, remove any excess soil, leaving 1 to 2 inches of stem. Store each clump of tubers in a ventilated box or basket. Fill the box with slightly moistened sand, peat moss or vermiculite and place it in a cool, dry location with temperatures that remain between 45 and 55 degrees F. Check tubers periodically through winter for rotting and drying out. If the tubers appear shriveled, mist them lightly with water. If any start to rot, trim the rotted portion of the clump so it wont spread. The tubers are fragile, so be careful when handling them.