“The Kratky method generally functions best when it uses either rockwool, hydroton, or coconut coir. Rockwool (pictured above) is made out of basaltic rock that has been spun into fine fibers and then packed together into cubes or blocks. Hydroton is made out of expanded clay pebbles. Coconut coir is made out of the shells of coconuts and is most often found packed together like rockwool. Using one of these three growing mediums is recommended because they come in larger sizes than many of the others. The large size prevents the growing medium from spilling out of the holes in the net pots that the Kratky method uses. Using one of these will also help to keep your Kratky method system cleaner.”