The first step is to have a large amount of dirt as the bottom layer. I use any organic mix, (no ferts added) It is best if you soak it in a separate container for a minute or two so you don't have bubbles coming up through your top layer once it is up. I like to mix it by hand so I know I am getting out all the major clumps. At this point plant heads add all kinds of ingredients, I like clay myself. The point is that plants take in up to 10x to 40x more nutrients from their roots. So success starts in the substrate from the start.