Grodan Stonewool (rockwool) is made from molten rock spun into cotton candy-like fibers and then compressed into cubes, blocks, or slabs. Where other rockwool brand manufacturers cut all sizes from one batch of wool, Grodan is unique by making different types of fibers. The purpose is to support the requirement of the plant in the different plant stages. Grodan has a tremendous capacity for absorbing nutrient solution while retaining plenty of oxygen for rapid plant growth. Grodan comes in graduated sizes. Seedlings started in cubes are easily transferred to blocks and then onto slabs, if desired. Seedlings or cuttings started in the Grodan cubes can also be transplanted into more traditional planters and growing mediums. Grodan Blocks - Grodan Delta blocks are the most uniform blocks available on the market. They feature improved grooves at the base to promote better drainage. They are available in a large assortment of sizes and configurations to suit all types of plants. These growing blocks are used for direct sowing or "blocking on" of Macro and Multiblock raised plants. AO 36/40 plugs fit well into the hole sizes provided by the blocks. The blocks can then be placed on top of a slab to provide for a larger growing volume. Hugo is the largest of the growing blocks. It provides enough growing volume to support a larger plant, so it does not need to be placed on top of a slab.