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Salts on Clay Pots

That white powder on clay pots

By: Sandy Feather 2006
Penn State Extension


Q. I have noticed a yellowish-white crust on the surface of the soil and sides of my clay pots on many of my houseplants. Is this some kind of fungus?

A. What you are seeing is the accumulation of soluble salts from fertilizers and the minerals dissolved in hard water. Fertilizers are salts, just like table salt, except that they contain plant nutrients. As the salt builds up in the soil, it becomes difficult for the plants to take up water.
 


Address the Problem

To minimize this buildup, be sure to water houseplants until the water comes out of the drainage hole(s) every time you water. It is easiest to put smaller pots in the sink or bathtub and water them there. Use a turkey baster to empty the saucers of plants too large to move so they do not sit in the drainage water. Otherwise, the soluble salts will be reabsorbed as the soil takes up the water in the saucer.

drainage hole in flower pot
Drainage hole in flower pot

Plants that grow in the same pot for a long time should be leached every six months or so by running water equal to twice the volume of soil through the pot. If salt has accumulated on the top of the soil, remove the top 1/4-inch of soil before you leach.

 


Correct Fertilization Levels

Be careful not to overfertilize houseplants. As a rule of thumb, do not fertilize them at all through the winter months when they receive less light and are not actively growing. Use a water-soluble fertilizers such as Miracle-Gro or Peters formulations from April through September. Once a month should be more than adequate for most foliage houseplants. Use a balanced formulation such as 20-20-20.

Those grown for their flowers should be fertilized more often, perhaps every two weeks. Be sure to use a formulation with a higher phosphate (the middle number) content to avoid pushing vegetative growth at the expense of flowers.

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