Gather the clay and/or plastic plant pots you wish to clean. Clay pots include terracotta pots. Wipe dirt, spider webs and other debris from the pots by using your hands or a small brush. Scrape off deposits accumulated on the inside and outside of the pots. Using a knife may be necessary for that task.
Mix one part household bleach with nine parts lukewarm water in a tub, bucket or sink, using plastic gloves to handle the bleach and bleach-water solution. Put one or two drops of dish-washing detergent in a separate tub, bucket or sink, and add water to that container. Mix the detergent in the container with the water. If the water does not become sudsy, then add more dish-washing detergent. Fill a third tub, bucket or sink with clean, cool water.
Soak your pots in the bleach-water solution for at least 10 minutes. Transfer the pots to the dish-washing detergent-water solution, and remove all mineral deposits and other debris from the pots. Scrub clay pots with steel wool or scrape them with a knife if necessary to remove the debris, and use a scrubbing sponge or scouring pad on plastic pots if necessary to remove their debris.
Rinse the pots in the third container's water. Allow the pots to dry.
Decorate your pots if you desire. Use craft-store cement and broken or store-bought mosaic tiles, for example. Another option is to apply a primer appropriate for plastic or clay, depending on the pots' material, and spray paint the outside of the pots. Alternatively, smear yogurt on the outside of the pots, and let them dry outdoors for at least one week, until they take on a whitish, aged appearance.