5 lb bag. Greensand works by trapping moisture in the ground at the layer of soil where plant roots feed. The natural mineral coating works like a filter, allowing water to seep in and holding it there until the plants needs it. A natural silicate that holds moisture in soil at root level Greensand is a naturally occurring, non-burning aggregate “sand” made of marine potash, silica, iron oxide, manganese, calcium and over 30 other trace minerals. Greensand can be safely stored practically anywhere, and safe to use around people, pets, and wildlife with no waiting period.