Does gravel at the bottom of pots improve drainage?

Many older houseplant guides advise putting a layer of gravel or stones in the bottom of a pot before adding compost. It is presented as basic good practice: the thing you do to stop soil from retaining water, which can cause root rot. The idea is that the gravel provides a place for excess water to collect below the root zone, keeping roots above the waterlogged area and allowing air to reach them from beneath.

The usual method is to cover the drainage hole with stones, then fill the pot with compost; the gravel layer will fill the bottom quarter of the pot and reduce available root space. In a simple test, two pots were set up—one with gravel, one without—and both were watered.

Pressing a finger into the compost just above the gravel in the first pot showed the soil there was wetter than in the pot without gravel.

gravel, pots, drainage, compost, root rot, houseplants, drainage hole, soil moisture, excess water, root zone