Orchid Growing Substrates

Important Parameters
With all we listed previously, we can start to work out a potting mix. Now, remains to design what are the
most important parameters :
Pots
- Clay pots will need a bit more water retentive mix.
- Plastic pots will need a less water retentive mix, and more draining one.
- Some growers in the USA use baskets lined with sphagnum moss. They give great results, however on
a commercial scale, that would be somewhat hard to imagine, getting a wood basket, eventually
plastic one, lining it from top to bottom with moss, hanging it and there are other options, so why
bother?
The MAGIC pH.
- There is one pH that suits all the species, except a few exceptions that will be listed afterwards, with a
specific how to pot part 5.7-5.9. There are in fact very few Paphiopedilum species growing at a higher
pH, or the measures were gross mistakes. Paphiopedilum armeniacum grows in fern roots and some
sorts of herb roots, at a quite acid pH of 5.3, however the whole clumps are growing on top of
genuine limestone, with a pH that can be measured at 7.5-8. But the roots never venture in that
alkaline limestone part, they are in the humic/acidic layer. As for Paphiopedilum rothschildianum, I
saw them in the wild some years ago, and again they did not grow in pure rocks or alkaline matters,
but in decayed leaf mould, fern roots, decomposing material, at a pH of about 5.9. True, there was a
lot of serpentine, but for sightseeing only, the rothschildianum roots were always in the humus cover.
- Asking Tony Lamb, who has seen more wild orchids than most people in this world from Sabah, he
said too that in his mind the plants need to be on the slightly acid side, because with all the effluents,
the rain passing through the canopy, decomposing matters and the material that always supported
the roots, he never believed that the Sabah Paphiopedilum needed alkaline conditions. He grew at
Tenom some fantastic clumps of rothschildianum, using leaf mould, tree fern, a few stones (but not
alkaline ones, more a kind of granite), and he did that again now in the Kipandi Butterfly Farm. One
can see as well at the Kundasang dozens of Paphiopedilum rothschildianum, stonei, hookerae,
volonteanum, on the ground, in a blend of leaf mould, debris, and tree fern, with some rocks to
prevent compaction. So much for the ‘alkaline loving’ Paphiopedilum.
- In Burma I saw Paphiopedilum bellatulum, growing in humus, extremely wet. It was hard to see any of
that ‘limestone’ and bellatulum is an acid loving Paphiopedilum, but with calcium carbonate available
at its roots. It seems complicated, but as seen previously, that’s the way to grow it.
- In the Netherlands, the target pH for most commercial potting mixes is 5.7, though some might say
that the Netherlands produce disposable plants. I think that the entire Floricultura motherplant
collections, grown in potting mixes buffered at that pH, is more precious than the entire stock of most
orchid nurseries around the world, yet they use the pot plant potting mixes.
- So our objective, to grow Paphiopedilum will be the pH of 5.7-6.
- Carbonate/lime availability.
Xavier Garreau de Loubresse
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