My thoughts on Silcon stim from a pod cast where I was listening to Dan Kittredge describe what plants do with the different elements. He stated that silicon is used for the outer cell walls of the plant . If you have abundant silicon than they show greater resistance to fungal disease. He also said that silicon comes from the mineral component of your potting mix rather than the compost. My potting soil last year was made of all organic material except for perlite. I struggled with my melon plants in the green house.