Store agar plates upside down. Stack the plates in their original bags for further protection from contamination.
Store agar plates in a refrigerator. Most bacteria cannot grow well in cold temperatures.
Store plates in a cold room if a refrigerator is not available. If you are storing plates in a cold room, check the plates for condensation a few hours after pouring. Condensation results from exposure to a heat source that drives water out of the water and into the lid of the plate. This will dry the agar out and render it unusable. Turn the plates over if condensation is visible and monitor closely for more condensation development.