Sun Gro Horticulture Black Gold Vermiculite, 8 quart Black Gold Vermiculite 8qt This naturally occurring material expands into layers under heat to become a highly absorbent, lightweight additive to potting soils and soilless mixes Its unique characteristics are sterile and neutral ph, which promotes faster root growth and improved anchorage to seedlings Vermiculite absorbs and holds both moisture and nutrients in the root zone while ensuring consistent aeration