For those readers interested in a little more detail about overwintering dahlias, here is a some more information that expands on the sidebar “Overwintering dahlia tubers: How Dahlia Hill does it” in the August 2011 issue of Michigan Gardener:
After the first hard frost in October, all the dahlia plants are carefully dug up by the Dahlia Hill Society members. Each plant can produce 5 to 20 new tubers, which are very carefully cut off the plant. They are individually labeled with a permanent marker and are rinsed in a light chlorine solution (5% chlorine to water; just enough to kill harmful bacteria). The dahlias are soaked in that solution for about 10 minutes, and then they drip dry on a screen for several minutes.
Next, they are placed into white plastic storage bags, as many as 40 or so in a bag (depending on the size of the tubers), and covered with fine, dry vermiculite. The bags are closed and folded over, but are not made airtight. The tubers are stored alphabetically in large, cardboard boxes, 3 to 6 bags per box. The basement storage room is humid and temperature-controlled to about 55 degrees.