The light weight of potting soil is also desirable if containers are to be moved. To prevent roots from being cooked, containers should be well insulated. Black vinyl cans used by nurseries are not suitable for garden use because black absorbs heat from the sun and the vinyl is so thin that the heat is transferred directly into the soil. Nursery cans may only be used if contained within larger containers or baskets. Wood pots and barrels are well-insulated and stay as moist as the potting soil within them, so roots will not desiccate as they come into contact with the inner surface.
Unglazed clay is probably the best material for containers.
It is very well-insulated and has good moisture retention. Roots that come into contact with clay cannot distinguish it from rocks or other material they may encounter if they were growing in the ground. Although glazed pots are not as appealing to roots, they are well-insulated and usually reflect sunlight. Because thorough drainage is necessary, it is important that dishes used to catch water are not allowed to hold it between watering. These are the most desirable for those who want fresh fruit available through the growing season.