Rockwool (also called stonewool or mineral wool) is an inert growing medium made by melting basalt rock and spinning it into fibres, then pressing it into cubes, slabs, or granules. It holds both water and air simultaneously, making it one of the most widely used substrates in commercial hydroponics and propagation.
Key Facts
- Inert, pH-neutral substrate β holds no nutrients, so growers have full control
- Excellent water-to-air ratio: retains moisture while maintaining 15β20% air porosity
- Available as propagation cubes (for seed starting and cloning), grow slabs, and granules
- Must be pre-soaked and pH-adjusted to 5.5β6.0 before use
- Non-biodegradable β requires specialist disposal; some operations recycle it
- Compatible with NFT, drip, and top-feed hydroponic systems