Eco-friendly SteadyGROWpro grow medium was engineered specifically for the germination, propagation, and growth of plants. It is produced using an aromatic-based system of thermoset carbon based polymers which creates a cell structure allowing for optimal water retention and air flow. Unlike rockwool, SteadyGROWpro can be safely ground for disposal or can be incinerated with no harm to the environment. The following products use SteadyGROWpro H+ media for maximum water retention.Plug Trays are 6 strips of 13 plugs in a standard 10" x 20" tray. 78 plugs per tray.