White chalky deposits on clay flower pots appear when the water that evaporates through the porous clay sheds minerals. The deposits are harmless but can be unsightly. Clay pots used both indoors and outdoors are susceptible to these deposits. Chalky stains are not a problem with plastic or ceramic pots, because the sides are impermeable to water. Cleaning clay pots is time-consuming but not arduous and it's possible to prevent most of them from forming with one simple step.
Empty out the flower pot. Use this opportunity to repot plants that have outgrown their containers. Rinse the pot thoroughly. Take large pots outside and use a garden hose.
Use a stiff brush to scrub off as much of the deposits and any remaining dirt as possible.
Make a solution of 9 parts water to 1 part household bleach. You can do this in a sink or bucket if you only have a few small pots to clean. Larger pots can be cleaned in the bathtub or large plastic tubs.
Soak the pots in the water and bleach solution for several hours. It's not likely that they will float, but weight them down if they do.
Remove the pots from the bleach solution and rinse them thoroughly. After they're rinsed, submerge the pots in clean water and let them soak for several more hours.
Take the pots out of the water and repot your plants. It's not necessary to let the pots dry before using them.