Granulated rockwool can be used alone or as an amendment to organic based mixes. For example, the addition of water absorbant granulate to peat mixes at 25-50% volume, increases water holding capacity and aeration, improving plant growth and shelf life. The water repellent granulates are superior substitutes for aerators such as perlite or Styrofoam. The granulate is prilled for easy mixing. Granulated rockwool as potting mix: When you use granulated rockwool to pot up your plants, the great advantage is that you never have to change the mix. The rockwool will last for the life of your plant. Rockwool's high water holding capacity will enable you to go on vacation without worrying about your plants drying out.