Q: I have some crusty-looking stuff on the bottom of a clay pot.
Can you tell me what it is and how to get rid of it? A: I think
you’re seeing efflorescence. This powdery material is the
remains of fertilizer or minerals in the potting soil inside the
pot. Water wicks through the clay pot wall and the minerals
dissolved in it dry on the outer surface. The white stuff is
composed of calcium, magnesium, sulphate, nitrate, phosphate and
ammonium salts. Simply soak the pot for an hour in a bucket of
water and scrub off the white powder.