To ensure that smaller terra-cotta pots emerge from winter storage intact and ready for spring planting, take the time to put them away properly in fall. First, thoroughly clean and dry the pots to prevent the growth of fungus and disease. Then, lay them on their sides, one tucked inside another, in a shallow wooden crate; store the crate out of the freezing cold. Never stack pots vertically -- changes in temperature and humidity will make them swell, causing them to stick together and practically guaranteeing breakage when you try to pull them apart.
Martha Stewart Living, March 1999