For many years, clay pebbles have been a popular hydroponic substrate. While the form and rough surface allow for entirely unrestricted drainage and plenty of air in the root zone, the rough surface holds a lot of water. Growing clay pebbles have significantly improved in recent years. With up to 3 times greater water retention and 12% more air retention than traditional hydroponic media, Grow Stones are a new player on the market. They have the capacity to hold more of the nutrient solution and oxygen that your roots require to thrive because they are made entirely from recycled materials.