Grodan Rockwool Cubes (1.5 Inches) 98 Per Sheet - Case of 30 Sheets An inorganic and sterile growing medium made from spun molten rock Superior medium for rooting cuttings 20% air space when saturated, and does not contain nutrients Condition by soaking for eight hours in a pH 5.0-5.5 and then rinsing with pH 7.0 water