Interior plant roots are usually in the bottom two-thirds of the pot. Therefore, you should not water until the soil in the bottom two-thirds of the pot begins to dry. You can't tell this just by looking. You have to feel the soil; not on the sur face, but about one-third the depth of the pot below the surface. For a 6-inch pot, stick your index finger about 1-1/2 to 2 inches into the soil. This is ap proximately to the second joint of your finger. If the soil feels damp, don't water! How damp should it feel? It should feel about as damp as a cloth you would wet and ring out prior to wiping a kitchen counter. Keep repeating this test until the soil is barely moist at the 2-inch depth. NOW, it is time to water! For larger pots, the one-third from the surface rule should be followed. For smaller pots, about one inch below the surface is adequate.
When testing for watering, pay attention to the soil. If your finger cannot penetrate 2 inches deep, either the soil is not porous enough or the plant is becom ing root-bound.