Question
Can I leave empty clay pots outdoors all winter (in Michigan) or will they crack in frezing weather?

Answer
Jack,
Empty clay pots can usually be left outside if they are upside down and are resting on a few small pieces of wood, rather than with the clay on the ground.  This is because damp clay may freeze on the ground and the rest of the pot may thaw, causing it to crack.  They need to be upside down so that no water collects in them, which will later freeze and expand.  The only clay pots that should not be left outdoors are the inexpensive Mexican kind that often have air bubbles in the clay.
I hope this helps!
C.L. Fornari