Hydrological Discontinuity…isn’t that a great 25 cent word! On Wednesday, I was doing some research for Nancy P. for her presentation on Container Gardening. I was looking up information about whether you should add a layer of drainage material in your containers or not.
The old saying, or myth, is that you should “add a layer of gravel or other coarse material in the bottom of containers to improve drainage.” A quick search for research based information brought me to the website of Dr. LInda Chalker-Scott from Washington State University. Dr. Chalker-Scott is a Horticulture professor at Washington State University who is known for debunking gardening myths with research-based information.
Dr. Chalker-Scott has a page devoted to debunking this myth. I encourage you to read her article. But essentially, what happens when you add coarse material to containers is that the finer material (or the material above the coarse material) must become saturated with water before the water will move into the coarse layer. So you are essentially doing the opposite of what you set out to do. You are not improving the drainage but making it worse.
I sometimes learn better by seeing, so here is a great visual that shows what happens.
So what is the take-away from this?
- Planting containers must have drainage holes for root aeration.
- “Drainage material” added to containers will only hinder water movement.
- Use good topsoil throughout in perennial container plantings for optimal water conditions and soil structure