>Admittedly, I currently use moss peat but Coir or rock wool may prove to be
just as good since these are relatively 'inert', non-alkaline, low nutrient
>media.
I wouldn't be too eager to try rock wool if I were you.
The rock wool craze has hit several countries before and time and time again
you see the 'rock wool disciples' turn round looking for something else.
The craze started in Holland as a wonder cure for growing almost anything.
Several of the large Dutch orchidfactories started using rock wool but in
the end this product didn't work for them. Sure tomatoes grow wonderfully on
them, but we're not growing tomatoes !
What are the disadvantages then ?
For starters : have you ever handled rock wool ? After a day your hands are
itching and if you have to work in it all day then a mask is recommended.
(in my parents orchid nursery we used the water reppellent kind in a mixture
with peat, we stopped using it several years ago)
Secondly, once you let a rock wool pot dry out, you have to repot the plant
immediately, there is almost no chance in rewetting the compost.
Thirdly, you are correct about the low nutrient content. There's nothing in
it ! Now I hear you all mumbling 'hey, nothing in it that OK for CP's!'
forget it ! Every plant needs a bit of fertiliser, there's always something
in peat, coir or whatever. CP's may grow in low nutrient conditions in
nature but they never grow in non-nutrient places (there's always a bird
passing over somewhere).
An additional problem is a requirement that most CP's need : an acid
environment. Now sadly this is the one thing that rock wool can't stand.
Rock wool starts to dissolve when the pH gets too low !!! Don't be afraid,
you won't have to worry about getting up in the morning and find nothing but
empty pots with helpless Cp's in them, it doesn't dissolve that quickly.
Fourthly, since we all care about the environment : you can compost peat,
coir, ... but what can you do with rock wool ? Nothing, this has proven to
be one of the main problems in Holland. After a few years the growers there
had enormous mountains of this stuff, they have tried to turn rock wool into
bricks, new road surfaces etc...
regards,
Kenneth Bruyninckx
akerne@innet.be