Grodan Stonewool Gro-Blocks Delta 5.6 - W/ HOLE - 3" x 3" x 4" - Stonewool is recognized the world over as an ideal hydroponics growing medium. Seeds or cuttings are started in these larger Grodan Gro-Blocks and, once rooted, the blocks are transferred to a larger stonewool slab. Gro-Blocks can be planted directly into containers for soil gardening as well. This is a strip of eight 3" x 3" x 4" Gro-Blocks, each with pre-formed holes. Grodan stonewool is known for its quality, consistency and performance. Holes are perfect size for any 1.5 starter plug.