Container drainage

Credit: Brand X Pictures/Gardening/Sandra Ivany

Intuitively, it seems that it should, but it can have the opposite effect. A movie seen in my student days showed how this really works.

The water molecules that move down through the soil experience a particular surface tension. When they come up to the much larger air holes between the gravel or plastic chips, they don’t have the pressure to “leap” into those large holes. Water backs up and eventually the downward pressure forces the water into those larger air spaces, so drainage is actually slowed. Add something like perlite to the entire soil mix to improve drainage.

I do recommend adding packing chips to reduce the overall weight of a container, if it is very deep.