Rock wool is a growing medium made from rock and sand fibers spun into shapes similar to the cotton candy making process. This medium is versatile and easy to use, making it popular for hydroponics seed propagation and plant growth. The benefits of using rock wool is that it retains water and holds air to improve the hydroponics growing process. Rock wool disadvantages are that it has a high pH that requires water amendments sometimes and it is not environmentally friendly because you cannot easily dispose of it.
Soak 1-inch rock wool cubes in water until the cubes appear hydrated. Use plain water until the seed germinates and the sprout appears.
Place the rock wool cubes in an empty germination tray. Drop one seed into each cube so it is set approximately 1/4 inch deep. Verify the seed germination depth for the plant type as it may vary slightly.
Apply water to the germination tray to make sure the rock wool cubes are thoroughly soaked. Cover the tray with clear plastic and set it in a warm location that receives indirect sunlight. Do not cover the tray if setting it in direct sunlight, as the temperature becomes too high for germination.
Monitor the moisture level of the rock wool cubes during the germination process to verify that they remain moist. Drain excess water pooling at the bottom of the tray. Move the tray to full sunlight and remove the plastic cover once the seedlings appear.
Mix a container of nutrient water according to the hydroponics nutrient instructions for the quantity of water. Sprinkle water evenly over the rock wool cubes once the seedlings appear, to keep the cubes moist without creating standing water at the bottom of the tray.
Transplant the seedlings to larger rock wool cubes once the true leaves of the plant appear. Set the small rock wool cube inside a larger cube. Choose a cube size that fits into the hydroponics system. Place the larger cube into the system to continue the growing process.