I just built a 2 ft high plant box in my backyard where I plan on growing veggies. I built it on the dirt and did not think about the fact that my back yard is made up of clay like soil. I have read mixed messages on putting gravel/sand at the bottom to avoid drainage issues. Does anybody have any insight on this. Has anybody used it and had success? Do you think I even need to worry about drainage issues since I will have about 1.5 ft of good soil to work with, and it is on soil (even though it's clay like)? If you all think I should put in gravel, how deep does it have to be to work? I would love any feedback.