Rockwool has long been among the most popular hydroponic growing medium on earth. Horticultural rockwool has been used for hydroponic growing in Europe since 1969 and produces 50% of their greenhouse grown vegetables. Yields have been recorded of up to 160 tons per acre, crop after crop, with greenhouse tomatoes grown in rockwool. Originally used as insulation, it was called “Mineral Insulation” and was later developed for gardening in Denmark. The main distributer of Rockwool is a company called Grodan, which means, “to grow the Danish way”.