Nowadays we use basically tree fern fiber alone or mixed to pebbles in many proportion, depending on the genus.
With Cattleya, the proportion is 1/3 of pebbles for 2/3 of tree fern fiber, with Cymbidium, is 50 to 50. For orchids with delicate roots, we just use tree fern fiber. With Vandaceous, we use nothing, just tie them to the hanging wood basket.
I would like to say that I am approaching the subject by the point of view of a big commercial orchid grower because for the small collections, the control is almost individual for each pot is easy and can be done, there is no problem to have the collection divided into many kinds of substrates and containers. But, in our case, as well as the other commercial nurseries, we need uniformity on the staging. With more than 150.000 adults plants, without counting the seedlings, there is no possibility to do differentiated watering.
Because of this and for many other reasons, in Terezópolis, all of our plants, except for Vandaceous and Oncidium, are planted in plastic containers.
We have already done experiences in alternative substrates and all of them can be considered disastrous. We tried to use only pebbles, it didn't work, it dries out excessively. We tried Acacia bark, a disaster. Due to low level of lignin and as a leguminous plant, it is too soft, retains too much water and hasn't enough oxygenation, the decomposing is processed in a high speed. Some times, in 6 months, it becomes a solid mass.
We have done a mixture formed by cork bark, small balls of polystyrene and sphagnum moss. First, if works well but then the chemical composition used in cork changed and didn't work any more. The cork sold is the residue of the cork stopper fabrication so it receives a chemical treatment inappropriate to orchid cultivation. Besides, it is a very expensive material. Solved the problem the control chemical products, it can work with a small collection but in a large extent, it wouldn't be economically possible.
And the sphagnum moss, isn't it a good substrate?
Nowadays we have at our disposal the sphagnum moss from Chile so good as New Zealand's, which doesn't crumble as our. It is an excellent substrate but not for all orchids. For Masdevallia and some orchids with delicate roots is terrific but its decomposing is very fast and have to be replaced every year.
It is excellent to recover plants and can be used in community pots. The watering control must be very rigid. Another problem is the very slowly growth, there is no way to be replace at short date. It becomes a very expensive substrate, not possible to a large extent.
However, concerning this question, many experiences are being done or had already done. In USA, far bark is very used, comes from California region. To use the bark from resinous trees, it is necessary to eliminate the resin they have. It seems that in the South of Brazil, it has been used and works very well but it is still very expensive. I've seen good results with this kind of cultivation.
Piassaba is another substrate which seemed to be very interesting but the continuous used proved that it doesn't work well. It has many inconveniences, it doesn't retain humidity, causes skin problems, it is very hard to touch, hurts manipulator fingers and hand. It is easy to manipulate 1 or 2 pots but you can imagine manipulate 12.000 with so hard product which doesn't permit the use of gloves to protect the hands. The glove should be very thick to prevent the fiber passes through it.
I can't talk about coxim because Aranda is not using yet. It is a very expensive substrate.
So, there is not yet a substitute for tree fern fiber?
After all, the tree fern fiber is the best alternative but organic materials will disappear and that is why they become more and more expensive.
The organic substrates are or will become impracticable for a big nursery. It is universal. Australia or New Zealand, where there are cultivation with organic substrates from native species, are facing the same problems.
In other words, no way-out?
In my opinion, soon or later, in a moment, we will start using the inorganic substrates. We'll take the same way United States and Europe got in. In this places, inorganic substrates like rock-wool and floral (derived from petroleum) are use. They worked very well if used in well controlled collections, very well organized. Inappropriate to out-door cultivation because they practically assimilate all substances, water, chemical residues of fertilizer, residues of medicines applied. The control of this excess must be rigid. Before applying fertilizer, the mineral salts presence must be carefully measured.
Who has succeeded in regulating all those controls, like the greenhouses orchids in Holland, has an excellent cultivation. Before adopting this method, we have to do some adaptations and researches in order to verify how the plant will react with the combination of tropic hotness, high humidity and accumulation of saline water.
We have to consider the alteration of the plant capacity to assimilate mineral salts and the alteration of chemical composition of those salts. Finally, how those substrates act and react under different conditions.
There is many differences between European and American climate and our and there are a rigid control of the temperature inside their nurseries. In low temperature, the metabolism is slow, has less power of assimilation. In higher temperature, it modifies but just until a certain point because above 27o C, the plant metabolize slowly again.
All those points should be studied before adopting those substrates. I have being observed this phenomena with Phalaenopsis, although there are warm climate plants, the excess of hotness affects their development. During the hot period of the summer, their leaves become softer. How they will react in a new substrate which retains more water?
Finally, In my opinion, we can't run away. In the future, we will have to use inorganic substrates because the organic ones will disappear.
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