Actually, perlite is an expanded stone (just like pop-corn).
The raw material comes from Greece and this stone is vulcanic.
This material is sieved in several gradations and comes that way to Holland or Germany.

The Perlite-producer will take this sand and heat it up to 1.000 oC and so it will expand and after cooling down you have the perlite.

This sounds easy but you can imagine that the temperature is very important, also the speed of warming up will have its influence on the quality of the perlite.
F.i. if you heat it up to much or to fast, the perlite will be to weak and can be destroyed easily.
If you heat it up to low, probably the perlite is harder but also less airily.


The reasons for using perlite are:

  1. Perlite will bring air in the potting soil. If you take a seedling substrate f.i., you know that the peat should be fine (otherwise machines will refuse or trays will not be filled properly) but that directly means that there is less air in the potting soil. By adding Perlite, you bring air in the potting soil and still it is very well possible to handle the potting soil in/on the machine.
  2. But, if you have a coarse mix, it does not bring air (the Perlite will “sit” in the “air-wholes” made by the coarse nuggets) actually, if I take 10 m³ of course peat and 1 m³ of Perlite, totally I will have 10 + 1 = 10 m³. But there is another advance of Perlite: it does not adsorb much water (only 2,5 times its own weight) but it adsorbs the water very easy and fast. So if you want to add water in a dry potting soil, it goes much faster with Perlite.
  3. This only counts if water is added from the top. The other way around is actually the opposite; the capillarity will be less with.

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