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Grow Mediums – Vermiculite

what is vermiculite

Vermiculite is a non-toxic mineral that is not only used as a growing medium, but also in the building industry, added to concrete, ceramics and can even be used as a pet bedding for animals.

Vermiculite is made up of small shiny mica crystals, when the crystals are heated to over 180 degrees Celsius, the water inside will expand due to the steam being formed, increasing the size dramatically.

The crystals can expand up to 3000%, creating a very lightweight texture and chemically non-reactive substance. This is a great material for absorbing chemicals such as fertilisers and holding in water and nutrients.

Vermiculite is durable and creates a good structure when added to soil. It has a neutral pH level of around 7, that usually mixes well to other growing mediums to create a quality mix. 

vermiculite
(CC BY-SA 2.0)

advantages of vermiculite

  • Great with water retention
  • Holds nutrients well
  • Can loosen up a heavy or dense soil
  • Does not rot
  • Good aeration and drainage
  • Mixes well with other soils 

disadvantages of vermiculite

  • Can be expensive
  • Not as effective when used alone
  • Does not aerate as well as perlite
  • Will fall apart after a long period of use 
cannabis growing vermiculite
(CC BY-SA 2.0)

how to use vermiculite

Vermiculite is best used with another growing medium. With similar characteristics to perlite, it actually has the opposite effect. Vermiculite holds water, while perlite will increase the drainage. These two growing mediums can work really well together, mixing in around 10% of vermiculite.

It can also work with soil and coco coir peat. You can mix 2 parts of compost to 1-part vermiculite and 1-part coco coir peat. Then add a small around (1 cup) of organic matter such as worm castings. Adding more organic matter will further increase the quality of your soil.