Should Rocks Be Put In Pots?

Q: Please settle a bet. Should rocks be put in a houseplant pot to help with drainage? 

A: Which side did you take? I sometimes say that folks who put rocks in their pots to improve drainage have rocks in their head. The reason may not be obvious but it is based on soil physics. Imagine the way water moves in a pot. When you water a potted plant, the moisture initially soaks lower and lower through the soil. Eventually some drains out of the bottom. Much, however, stays in the soil at the bottom of the pot. The soil there becomes saturated with water. But soil above that area is only moist and roots thrive.
As you know, roots suffocate and die when they are surrounded by water-filled soil because the roots can’t breathe. When rocks are placed in the bottom of a pot and then covered with soil, there is less soil in the pot above the saturation zone in which the roots of your plant can grow. When you add rocks to the bottom of a pot the result is a higher proportion of harmful, water-logged soil.