Answer: Rockwool is a sterile, inert planting medium made from fibers spun from molten mineral rock. Inert media don't harbor disease or pest that soil can and discourage the problem of "damping off." Rockwool has a porous structure that allows an air/water ratio that is good for seed germination and rooting cuttings. Rockwool comes in loose fibers, a loose "greenmix," plugs, and planting blocks. (Note that it is not the same as a water-repellant rockwell that is used in construction.) Loose fibers can be added to soil mixes or used for root cuttings. Plugs are soaked in water for 20-60 minutes and then seeds or cuttings are inserted. To monitor water levels, gently squeeze. If water comes out the surface, then no more is needed. If not, stand it in water for a few minutes only. Don't waterlog, or it reduces the aeration. When roots appear, transplant the entire plug into a soil mix. Rockwool will disintegrate over time.
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