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 also be planted directly into containers for soil gardening. This is a strip of six 4"x4"x2.5" Gro-Blocks, each with pre-formed holes. Grodan stonewool is known for its quality, consistency and performance.