Rockwool Starter Cubes (49 Cubes (1/2 Sheet of 1.5")) Root Cuttings, Clone Plants, Start Seeds and more! Perfectly-sized to fit a standard flat growing tray (or 1/2 tray) Predrilled planting holes make seeding and plant propagation a breeze! Optimum water and oxygen retention for seedlings Branded 5GallonBucketHydro. Don't accept substitutes!