Crops grown in containers, whether indoors or outdoors, must be grown in planting media that contains at least 2% by dry weight or volume of minerals (sand, silt, or clay, excluding perlite and vermiculite) at the start of the production cycle. There must also be a biological fraction which contributes to soil structure; and except for seedling/starter mixes, the media must be composed of at least 10% compost by volume. Pre-mixed planting media may be used but keep in mind that all products must first be approved by the Certification Committee. Planting media must contain no prohibited substances.