Introducing FloraFlex® RockWool, a hydroponics grow medium for soil-less growing. Rockwool grow cubes are created by spinning together fibers formed from melted basaltic rock. This forms a sterile substrate for your plant roots to take hold. Because a rockwool growing medium is a manufactured product, it does not contain any important nutrients or organic compounds to supply sustenance to your plants. Plants rooted in rockwool grow cubes will need a complete fertilizer solution to ensure they experience vigorous growth.