Don’t confuse “substrates” with “compost. The compost is but one of several ingredients in a substrate. A substrate is a mixture of 6 or 7 ingredients, which together, gives your container the below described characteristics. The compost is the ingredient which has all the nutrients. It is a pure “fermented” solid, organic material, decomposed and turned into dense fertilizer over 8 weeks time. This compost is one ingredient (25 to 30%) of the substrate.