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What Is Rockwool (Growing Medium)

June 02, 2022 2 min read

What Is Rockwool (Growing Medium)


Rockwool is hands-down the ultimate growing medium for germinating and raising seedlings due to its high aeration and good water retention properties. It's easy to use and hard to fail with! Rockwool is the product of molten rock which has been spun around at high heat (similar to fairy floss). The result is a light material with thousands of tiny cavities that help store water and air. The main features of rockwool are:

  • High success rates
  • Sterile
  • Great water retention
  • Great root aeration
  • Affordable and easy to use
  • Light weight

Using rockwool for germinating seeds

To germinate seeds in rockwool; make sure that the rockwool cubes have been fully soaked, place 2-3 seeds in the hole at the top of each rockwool cube. Make sure the seeds have been "activated" by wetting them with some water to help them germinate. Ensure that the rockwool cubes are sitting in about 1cm of water as this will help them stay hydrated. To maximise success with germination, you can use a clear glass or plastic cup/bowl/container to create a warm and humid greenhouse effect which can speed up the progress of your seeds sprouting.

Using rockwool to root cuttings

Cuttings can be rooted in rockwool too! Prepare by soaking the rockwool cube in water, then simply cut the parent plant as you normally would (usually just below a "node" on the plant stem), and then trim some of the unecessary leaves back. Dip the cutting in rooting hormone (optional) and embed the cutting slightly in the hole at the top of the rockwool cube. Keep the cutting in bright indirect light

Rockwool is stable and has no adverse environmental impacts - the product can typically be disposed of in an ordinary landfill (local regulations may apply).

That's everything on rockwool. If you wan't to learn more, check out the rest of our series: