Earth Growing produces green roof modules from expanded cork, as an alternative to plastic trays. The cork is derived from the residual flow of bottle stoppers, which in turn are made from the bark of the cork oak. This has been used to build a pilot plant where Dutch wool, currently a waste product, is being tested as an "additive" in the soil mixture (substrate). Sheep wool can keep the other ingredients (compost and ground roof tiles) aerated. It can also buffer water and decomposes slowly, releasing nutrients for the plants growing in the substrate.
