Superior to Rockwool Blocks. They are lighter, and wet instantaneously with enhanced root growth. They do not break or fall apart and there is no dust and no mess. They are also free of pathogenic organisms and require no pretreatment or further sterilization. STG Grow Blocks are designed to accept plants grown in commonly used propagation starter cubes or STG Grow Cubes that have already rooted or sprouted. When the roots in the STG Grow Cubes are exposed, they are ready to be transplanted into the larger STG Grow Blocks.