I may take some criticism for saying this, but it is a myth that rocks, perlite or any other stuff at the bottom of the pot improves drainage. Putting stuff in the bottom of the pot only reduces the amount of space for your roots. Rocks or perlite do not suck the water out of soil-- the soil will continue to hold just as much water regardless of the material under it. In fact, changing mediums within the pot only slows water movement.
