Hands up anyone who puts stones, gravel or 'crocks' (pieces of terracotta pot or broken crockery) in the bottom of their pots before filling them with compost. I imagine that will be most gardeners because as everybody knows, putting crocks in the bottom helps drainage. Well, that actually isn't true and was disproved nearly one hundred years ago. Plants cannot survive in saturated soil, their roots need air and eventually will drown if the soil remains waterlogged. Stones or crocks can actually prevent water from draining out through the holes at the bottom of the pot as water molecules are subject to forces of cohesion and adhesion. This basically means they like to stick together or stick to other things causing the capillary action that pulls the water up into small spaces. The crocks form a layer called an aquitard, a layer impenetrable to water, and the soil above would become saturated before the water was forced to drain through the bottom layer. So what is the answer? Use paper towels, coffee filters or even newspapers to line the base and then stand the pot on 'feet' so water can drain freely away though the holes in the bottom.