Caseyhoo showed a good example of what I meant, but here's one of my growing containers as another example. It's used to be a meat bin in a refrigerator until the refrigerator broke.
The area in the corner is composed of cinder, which is where the container gets its water. I have an automatic watering system, so I simply bury a watering stick in the cinder, and the medium isn't disturbed when watered.
Here's a hole in the side of the container to drain excess water.
Here's another container. This one is more conventional. The drainage hole is on the bottom, but the container gets watered 3 times a day, so the medium stays wet.
