Orchid Growing Substrates

Mosses
Historically mosses were used for potting orchids for centuries. It is clear too that some early Chinese and
Japanese grower’s manual, when speaking of moss, did not consider Sphagnum moss, but what we call ‘sheet
moss’, or ‘wood moss’, which is the usual growing media of quite a few Paphiopedilum species. It is as well
the usual growing media of quite a few epiphytic species. However, there are a nearly infinite number of
mosses genus and species, some suitable, some not. Lance Birk, the noted Paphiopedilum grower, did design
a mix using bark and sheet moss nearly 40 years ago. It is a very successful mix, partly because most sheet
moss has a poor buffer capacity, and therefore will not remain acid for a long time. It is aerated, and moss can
regrow in the pot. However if the moss dies, it will kill the plant by decomposition after a while, and
depending on the temperature, the feeding and other elements it can become really sour suddenly. Xavier
used successfully moss in the mix; however it has now been replaced. Irrational thinking’s can always come,
and when using sheet moss and bark, the plants grow well, notwithstanding the decomposition of the
potting mix, that can be pretty fast. The next question was to find out what the moss really brings to the
plants, and, apart from some water retention, that can be easily reproduced with other materials, or adjusting
the watering frequency, it provided, through its decomposition, organic compounds and micronutrients. The
microflora harbored in the moss could have had its importance, but so far the effects can be reliably
reproduced without the use of sheet moss anymore. Study the two aspects of a product, physical and
chemical, that’s the key to find how to replace some ‘magic ingredients’.
Sphagnum.
- Sphagnum moss is probably one of the most popular compounds around the world. It has been used
for a long time, since the early days of orchid culture. In the 19th century, live sphagnum moss was
used mixed with osmunda fern roots. It is important to note that the sphagnum used was from
Europe at that time, and alive. In the USA, sphagnum harvested locally was used too, with various
successes. Many growers reported that some ‘colors’ and structure of sphagnum grew pristine plants,
where some other ‘colors’ especially the red small headed types were strongly phytotoxic to the
plants. Now, we know that there are many sphagnum species, and some can even colonize sodic
marshes, pure water stream, forests, bogs and swamps. In Europe the harvesting has been strictly
controlled and prohibited subsequently, as sphagnum became rarer. Anyway, with the tissue culture,
and the massive productions starting in the 50’s of many hundreds of thousands of plants around the
world, it was not feasible to harvest sphagnum in Europe and the USA to re-pot such plants.
Sphagnum was used in Europe commercially until the mid-90’s as a local harvest in France and
Germany, with some further supplies from Denmark. However, most European sphagnum moss
would not last very long, and it was always preferred live. The attempts to use it dried were
sometimes successful, sometimes not, and anyway it required a very low mineral salts content of the
water not to decompose. Most moss from the Northern Hemisphere would not become a popular
commercial success, because of problems of availability, lack of resources, especially renewable ones,
and the fact that most of the easy to harvest sphagnum moss did not react well to many chemicals. As
an example, the French Sphagnum moss would become gray and metallic smelling nearly overnight,
killing the plants, after a single application of either a copper compound, or fosetyl-al fungicide, or
even of some fertilizers containing urea.
- First, there are some things to state about Sphagnum moss. A lot of misconceptions arise around
‘sphagnum bogs’, and again ‘very low mineral content’ sphagnum moss. In fact, sphagnum moss
tends to grow first in full sun for the commercially harvested varieties, with its ‘feet kept cold’. In New
Zealand, it grows on apparently very old grey clay, with a junction that is wet, and the fibers are
Xavier Garreau de Loubresse
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