I don't because I am usually stoned and forget. Plus my PRO-MIX drains so well I don't worry about making mud in the bottom of the pot.

However, it is a good idea to put lava rocks at the bottom. They retain moisture but are very pourous and airy.

You can place the lava rock (small pebble size) at the bottom about an inch high, or, just enough to cover your side drainage holes.

Happy Growin.