Humboldt Roots is a highly concentrated organic root stimulant which, when used during the critical growth stage, expands the root zone of your plants. Large yields are directly related to a plants metabolis Humboldt Roots is a highly concentrated organic root stimulant which, when used during the critical growth stage, expands the root zone of your plants. Large yields are directly related to a plants metabolism rates. Plant metabolism rates are directly related to their root zones uptake of nutrients and fertilizers. Humboldt Roots' job is to expand the root zone, and it knows how to get things done. Humboldt Roots gives you larger yields through increased metabolism.