Question
How on earth do I get rid of the white moldy looking substance on the outside of all my clay pots.  I have 18 plants in clay pots and 12 in plastic pots, only the clay ones have this substance.   HELP....... have already tried warm soapy wash, I don't want to hurt my plants in the process of removing the substance.  

Answer
Hi Cindy,

There are several ways to clean up the salt build up on clay pots.  The first is to simply scrape it off with any sharp tool or a wire brush, but that can also mar the pot.

The white deposits are the concentrated organic salts from the application of water soluble fertilizers or can be from water rich in magnesium or calcium carbonates commonly found in hard water areas.

Try first to put the empty pots in the dishwasher, and run through the longest cycle.  The sodium salts of the dishwashing detergent will "force" the calcium and other chemicals into solution to be washed down the drain.  Depending on the severity and thickness of the deposits, this may take several washes.

Another approach is to allow the pots to soak in a bucket covered with water.  You may add a cup washing soda(sodium carbonate  NOT SODIUM BICARBONATE)/5 gallons water and soak for several days.

If you want to do this quickly and don't have the patience to allow the pots to soak in the water, you can also use dilute solutions of muriatic acid (which is also used to clean paving tiles and masonry).  This can be very dangerous, and unless you are certain that you can safely handle the acid (hydrochloric acid = muriatic acid), I would use that as a last resort.  There are other weaker acids, such as phosphoric acid that can also be effective.  Check with your hardware store and ask about acids used to clean masonry and cement.  These will all be safe for clay pots.  After the acid bath, the pots must be rinsed thoroughly, and I would suggest soaking in clear water after rinsing.

Good Luck and Good Gardening.