Module 3 · Soil & pots — roots need air too
lesson 3.2
14 / 33
Lesson 3.2 · 6 min
The gravel-layer myth
After this you will stop adding a gravel layer and understand why it backfires.
Almost everyone is told to put a layer of gravel or crocks in the bottom of a pot to improve drainage. It sounds obvious — water flows through gravel, so it must help. It does the opposite, and the reason is a bit of physics called the perched water table.
This one surprised me, because it is repeated everywhere. But extension horticulture research has shown it for decades: a coarse layer under the potting mix perches the water higher, it does not release it. The thing that actually drains a pot is a hole in the bottom and a mix with structure — nothing you layer underneath.