Grodan A-OK 36/40 1.5 Inch Starter Plugs, Sheet of 98 Grodan A'OK plugs are designed for seed and cutting propagation prior to "blocking on" into larger growing blocks Grodan Stonewool (rockwool) is made from molten rock spun into cotton candy-like fibers Seedlings or cuttings started in the Grodan cubes can also be transplanted into more traditional planters and growing mediums The purpose is to support the requirement of the plant in the different plant stages The V-shape design of the plug discourages tangling of roots AO grodan rockwool plugs made of molten rock spun into cotton candy-like fibers and then compressed into cubes, blocks, or slabs The purpose is to support the requirement of the plant in the different plant stages a tremendous capacity for absorbing nutrient solution while retaining plenty of oxygen for rapid plant growth Measures 20-inch length by 9-4/5-inch width by 1-1/2-inch height