Coarse Perlite Horticultural Seed Starter Improver Soil Structure 12.5 oz provides aeration and drainage, yet retains and holds substantial amounts of water that it releases when needed sterile media for drip or passive hydroponic systems, ideal for growing delicate plants such as lettuce increases the nutrient holding capacity when water-soluble fertilizers are used As Perlite is sterile, it is free of disease, weed seeds and insects. Chemically inert, does not deteriorate and has an essentially neutral pH