Eliminating the Moss and Algae Growing on Clay Flower Pots

February ,1999 I recently repotted an English ivy. I received this during the Christmas holidays. I repotted the plant in a new clay pot, but after 10 days or so, there was a pale, green-white material on the outside of the pot. Could this be mold? The plant is placed in a northern exposure window, (the only place my houseplants will grow). I don't think I have overwatered. There is a drainage hole in the bottom. We live in zone 6. Could you please help????? Clay pots are better for your plants because they breathe and allow more oxygen to the roots. That is just algae growing on your pots. Unfortunately that is a drawback to using clay pots. It won't hurt a thing other than the looks of the pot, but if it remains on the pot long enough it will stain. The algae can be removed from the pot with warm soapy water, and if you add a little bleach it will even slow the algae's return. Unfortunately, unless you are growing cacti in the clay, algae is inevitable. Another drawback is that clay pots dry out more quickly than other containers. Therefore you must be more vigilante in your watering. I would suggest that you set the pot inside of a ceramic or plastic pot with a layer of gravel in the bottom. This will hide the algae, and at the same time help the plant to retain it's moisture..