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Perlite or Vermiculite?

Can someone please explain which is best for mixing with MPC to make a lighter medium for cuttings.Do they have different uses? I'm confused which to use and for what!

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  • pansyfacepansyface PEAK DISTRICT DerbyshirePosts: 18,682

    Another forum and some time ago, but this may help.

    On Fri, 8 Apr 2005 01:32:20 +0100, "Miss Perspicacia Tick"
    wrote:

    What's the difference and when should one be used in preference to the
    other? As I understand it, both perform the same function - that is to
    improve drainage; should the former be used with cuttings and the latter
    with more established plants (i.e. if you're repotting)? My father appears
    to use them interchangeably but I reckon that, if they could both be used
    for identical tasks, then why would they both be sold? I was potting on some
    mystery plants (mystery because they were something new I'd bought and I'd
    lost the packet and brain fog means I forget my own name sometimes!) and I
    didn't know which to use, so I used vermiculite simply because we had more
    of it.

    So could someone please explain the difference to me (Monty Don only appears
    to use vermiculite - I was hoping he'd use perlite for something so I could
    fathom it out for myself)?

    Thanks

    Vermiculite starts life as a relative of mica, which is flash heated
    to a few hundred degrees C, when the water bound in the crystal
    structure instantly turns to steam and expands the mica-like sheets to
    give the result you see. The name comes from the latin 'vermis' - a
    worm.

    Perlite starts life as a volcanic glass, which is crushed and then
    also flash heated but to a rather higher temperature than vermiculite.
    The glass softens and water within the glass converts to steam and
    foams up the glass. Not sure whether it's an 'open' or a 'closed' foam
    structure though, i.e. whether the pores are interconnected and open
    to the outside world, or whether they're just a mass of sealed
    bubbles.

    IME, vermiculite has an alkaline pH. I used to use it in potting mixes
    for heathers but didn't understand why the foliage was getting
    chlorotic (yellow), until I tested the pH of the vermiculite. I now
    only use perlite.

    Vermiculite can get quite soggy, but perlite doesn't to nearly the
    same extent, so I suppose the argument that it retains moisture better
    than perlite is probably true. But I also feel that vermiculite can
    inhibit drainage, especially in potted plants, due to the flat platy
    nature especially of the larger particles, and after it's been around
    for a while. OTOH I am quite happy with the idea that vermiculite
    retains nutrients better than perlite, due to what is known as its
    'ion exchange capacity', whereas I doubt that perlite has an exchange
    capacity of any consequence.


    --
    Chris

    E-mail: christopherhoggvirginnet

     

    Apophthegm -  a big word for a small thought.
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