Rapid Rooter® plugs are all natural soilless grow plugs made of composted tree bark and organic materials. These plugs are perfect for seedlings or cuttings. Transplant plugs in soil or soilless hydrogardening applications. The composted bark gives off a natural rooting hormone that helps promote rapid rooting. These starter cubes also have large quantities of beneficial microbes that colonize young roots and help young plants to resist disease while maximizing nutrient uptake. The Rapid Rooter Starter Tray comes pre-filled with 50 plugs.