Grodan horticultural grade rockwool consists of a mat of long, fine fibers, spun from molten natural rock. It is inorganic and inert, very light when dry, sterile, is not biodegradable and has a very high water and air holding capacity.
Rockwool is mainly used in hydroponic flower production and generally is not widely used by the home grower apart from its use as a propagation medium.
The most popular brand of rockwool is of course Grodan, made in Denmark since 1969. Grodan rockwool has been widely recognized as the ideal growing substrate. Suitable for almost any growing application, Grodan rockwool is known for its ease of use, cleanliness, quality, and consistency.
Grodan is made from basalt rock and chalk and in the manufacturing process that are heated to 1600°C, to create lava. The lava is then blown into a spinning chamber, which makes fibers similar to cotton candy. The fibers are packed into mats, from which Grodan cubes, blocks and slabs are then produced.