Horticultural Vermiculite has the excellent property of improving soil aeration while retaining the moisture and nutrients necessary to feed roots, cuttings, and seeds for faster growth. Like perlite, horticultural vermiculite is permanent, clean, odorless, nontoxic and sterile. It will not deteriorate, turn moldy or rot. The pH of vermiculite is essentially neutral (7.0-9.5) but owing to the presence of associated carbonate compounds, the reaction is normally alkaline. It also will vary (become more alkaline) with changes in processing techniques and time, and with the presence of moisture. The pH, color and chemical composition of vermiculite also will vary from mine to mine. Medium Grade.