Grodan Gro-Block Improved GR22 Jumbo with Hole, 6" x 6" x 4" (Case of 64)Grodan Gro Block Improved GR22 Jumbo with Hole, 6" x 6" x 4" Case of 64 New and improved stone wool substrate with advanced wetting technology from Grodan Introducing Grodan Gro Blocks Improved, a product specifically engineered to deliver real results for your crops, developed by plant scientists, researchers, and top growers. The uniform distribution of water and nutrients throughout the block allows for more efficient use of the entire substrate