vermiculite
 

How durable is pure vermiculite? I have phal stuartiana up for repotting: it's in coarse bark now, but the bark has begun to decay. I'd like to try to grow it in pure vermiculite. Never used pure vermiculite before, though, so if it's a bad idea pls let me know. Thanks in advance!

Its not a bad idea but you need to mix it with other media...by itself it is tiny particles; unless you can get the large ones average 4to 6 mm at least...the commercial ones being sold are fine and sandy and I dont think your phal will like that...I have a phal on LECA on S/H method where the clay pellets are 4 to 8 mm in diameter.

I would advise against vermiculite. Like Bud said, most kinds you can get are very much like sand, and when wet, it compacts very much. I recently had changed my houseplants' potting soil to a mix with vermiculite - all but the nephthytis and dragon trees hated it. It would be far too smothering for a phal, and I'm not sure how it would work in a mix with bark, perlite, or charcoal. It may just end up sticking to that when watered.

Vermiculite is usually used in mixes (for both orchids and normal plants) to increase water retention and aeration. So I assume that a vermiculite-only mix would take a very long time to dry out, which is definitely not a good thing for orchids. IMO, if you want an inert potting medium, you are much better off using hydroton/leca.

Yes, not only does vermiculite/sponge rock retain water it compacts !

There are many brands of leca (light expanded clay aggregate). Hydroton, Prime Agra, and AliFlor come to mind.

I agree with camille and the others that it would be too fine, sandy and moisture retentive. New course bark would last a year or two and it's what the plant is used to.

They are also no longer recommending vermiculite as inhaling the tiny particles can cause lung cancer.

I have got seedling that used it in a mix and the roots where rotted.

I recommend a mix of LECA, CHC, and charcoal and use a airy pot. You my have to water more but helps alot in keeping the roots heathy.

Thank you all for the fast reply! My other phals have all been repotted at least once, they are all either in sphag or in fine bark (this is a low-humidity environment, indoors under a ceiling fan; coarse bark holds too little water when it's new, too much when it's old; not good either way). This phal is the last one I haven't moved out of its original medium yet, so I wanted to try an inert medium to see if it works better. Guess it's time to shop for LECA :) . Thanks again! Dima.