I have been awarded a contract to plant 5 Large Jap. Maples which will be planted in very large ( say 200+ gallon) concrete pots which are located in the lobby os an office building. As for the soil medium, I am using a general purpose topsoil with a light amount of organic humus. I was wondering if the large concrete planters need to be able to have some type of drainage, or should some absorbing material be put in first. My concern is that a fungus or rotting may occur. Or will total soil be OK?