The potting medium is pure coarse perlite, nothing else. I try to use shallow pots also. perlite can retain a lot of moisture in deep pots and for plants that don't like that, its dangerous for root rot. It can be a bonus if your too light with the watering or going away for long periods. If your over doing the watering ( like me ) shallow pots dry out quickly so its not a problem. I also feed the plants every time I water. Its very weak but since the perlite gives nothing in the way of food, you have to feed. The plants seem to be benefitting greatly from it also.