What is vermiculite?

Vermiculite is a great way to improve soil structure in gardening as it improves aeration, increases moisture retention and holds on to essential nutrients.


Vermiculite is a naturally occurring mineral composed of shiny flakes resembling Mica. It is produced in different grades and sizes. When heated to a high temperature, vermiculite flakes expand 8 to 30 times their original size and lose weight.


In general, coarser grades of vermiculite are used for loose-fill insulation, potting mixes and a growing medium in gardening horticulture, whilst finer grades are used in building boards and in carrier applications for animal feeds.


Exfoliated vermiculite is an excellent germination and potting medium for gardening and horticulture; it can also be mixed with other mediums. Vermiculite is sterile and therefore needs to have nutrients added to the growing mixture. Vermiculite is used in potting mixes in horticulture and gardening for the following reasons:

  1. It improves aeration.
  2. It increases moisture retention.
  3. It holds onto essential nutrients and minimises fertiliser leaching.
  4. It has a near neutral pH.
  5. It is inorganic and sterile.
  6. It is much lighter in weight compared to other mediums.



Vermiculite is ideal for the germination of seeds, because its aeration properties combined with its water-holding capacity make it a very suitable medium for direct contact with the seeds. When vermiculite is used alone, without compost, seedlings should be fed with a weak fertiliser solution when the first true shoots appear.

  1. Sow seeds into pure vermiculite or mix with peat or pine bark in seedling trays.
  2. Press seeds down firmly and cover with a layer of vermiculite and spray with a fine mist daily.
  3. Seeds will germinate within a few days. It is important to add nutrients after a few days, as vermiculite is sterile.
  4. Transfer seedlings into beds; the roots are protected with vermiculite, which acts as an insulating and moisture-retaining medium.



Mix vermiculite in roughly equal proportions with clay soil to absorb the excess water as well as to lighten the soil. Similarly, mix equal parts of vermiculite with sandy soil to aerate the soil and stop compaction. This will improve both its water-holding capacity and its surface tension.


Vermiculite mixed with potting soil or compost gives a very light compost, which holds more water and thereby lengthens the time between watering; the compost will also retain more nutrients. Mix equal parts of vermiculite and potting soil to have lighter hanging baskets and containers.

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