Q. I have noticed a white substance accumulating on the soil and edges of my houseplant pots. What is causing this?

A. This is probably salt residue caused by an excess of soluble salts in the soil. If your plants do not have proper drainage, or if you are watering them too lightly and too frequently, a buildup of salts can occur. Soluble salts can also be found in fertilizers or in excessively hard water. Such residue can be prevented by occasionally watering your plant heavily and flushing out the salts. If you live in an area with very hard water, you might want to water your plants with distilled water.