KINDS OF SUBSTRATES AND SUPPORTS FOR EPIPHYTIC ORCHIDS
by Delfina de Araujo
There is no ideal substrate for all epiphytic orchids but until now the tree fern fiber is the one which congregates more qualities to occupy this place. Nowadays, the big challenge to the orchids growers is to find its substitute because the tree fern fiber commercialization is about to be forbidden by reason of the Dicksonia selowii's extinction. Although it has been replanted (unfortunately in a small extent), there isn't a true replantation program. The consummation is bigger than the production because it grows very slowly. It can also be extracted from Osmunda, Cyathea and so on...
The purpose here is putting this question under discussion by knowing some commercial and amateur growers' opinion and experience.
The substrate should have many proprieties: It must retain humidity for a while without getting soaked, to be able to hold the plant firmly (a plant which is not firm never sets healthy roots), to be easy-to-handle and to be long lasting. Another important point is the substrate's pH, the efficacy of absorption's fertilizer depends on its acidity.
Some cultivation media such as cork bark, nylon foam, palm's fiber (piaçava, Attalea funifera and Leopoldina piassaba) are inert because they don't have food values for the plant which needs to be integrally nourished by fertilizers. They are considered just a support. Some other cultivation media such as tree fern fiber, osmunda, tree bark, sphagnum moss and coxim are considered the genuine substrates because they provide food although the plants remain needing to receive a complement by a regular fertilizer application.
Inert cultivation media
Expanded clay is a potting medium that requires high fertilization. It is not recommended for small pots (seedling) because it dries out quickly. However is highly recommended for the big and medium ones instead of using pebbles to former the drainage's layers in the bottom.
Pebble is used mixed to tree fern fiber in clays or tree fern fiber pots and plastic containers for Cattleyas and Dendrobium phalaenopsis but it is not indicated for dry climate because it doesn't retain humidity.
Cork bark is indicated to Cattleya, Oncidium and Coelogyne species.
Piaçava (Palm's fiber): The one used to cultivate is the remains of broom fabrication. It dries out very quickly and doesn't require drainage's layer on the bottom. When the plant requires a high level of humidity, you must mixed it to sphagnum moss in the proportion of 1/3 of sphagnum for 2/3 piaçava.
We can't remove a plant from tree fern fiber substrate directly to piaçava, first we must used it mixed to tree fern fiber or sphagnum moss and later, we can use it alone.
This support doesn't have food values but there are some advantages: it doesn't retain water, grease or dust. Besides it doesn't have dust remains as tree fern fiber, for example. It allows a good ventilation provides it is not too much compressed when reppoting. Indicated to high humidity level places like Petrópolis.
In Rio de Janeiro, sometimes, the plant refuses to bloom. Some years ago, it was considered as promising support however, against all expectations, it revealed not to be adequate for most part of orchids perhaps due to fact of the lignin presence which inhibits the decomposition.
Commercial growers who adopted it some years ago are returned to the old system of using tree fern fiber because the results fallen short of their expectations. Perhaps it could work in a very small collection.
Charcoal, provides it has not been treated for burning in barbecue, gives excellent results in rainy places. There is no decomposition and never gets soaked. Working as a filter, it controls the acidity when mixed to tree fern fiber, extending its use for more time. There are two main disadvantages, because of its weightless, it can't hold the plant and due to its porosity, it accumulates mineral salts. It must be often watered of pure water to wash those salts. It is good for orchids which don't like having theirs roots wet such as Vanda, Ascocenda, Rhynchostylis, Renanthera, etc...
Tree bark decomposes very easy in the tropics because of the humidity, hotness and bacteria. Another preoccupation is tannin which must be eliminate before using.
Peroba bark ( Aspidosperma polyneuron) is indicate for some Cattleya species such as walkeriana and nobilior.
Pinus eliottii, it must be boiled before using to eliminate the tannin and the resin.
Coxim is a semi-industrialized product from the parenchymatous tissue of the coconut bark and seems to have many nutrients. Before using, it must be immersed in water, daily renewed for, at least, 8 days in order to eliminate the tannin.
It is found in cubes, granulated, logs, slabs and sticks, each has its own needs concerning the immersion. It can be kept in a plastic container for many months to used be according the needs and won't presents any decay.
It also seems to retain too much fertilizer in its tissues accumulating excessively mineral salts. Just fertilizer with nitrogen and apply every 3 months, a soap spoon of urea solved in 10 liters of water or a mixed of Ricinus communis'bran and bone dust. Unlike to other substrates, don't wait for the completely dry out before watering again. However, you must pay attention because it retains (according to the producer) twice its weight in water.
The upper layer dries out and the inferior ones maintain the humidity. It seems to be long lasting, 4 years in high humidity place 8 years in a drier place. At first sight, depending on the climate conditions, the results are more satisfactory when used in plastic containers than in earth pots.
Sphagnum moss is specially indicated to those plants which need high level of humidity like Odontonia, Sophronitis, Miltonia, Paphiopedilum .
It can also be used for Phalaenopsis provides it is in a clat pot, mixed to tree fern fibre and close to the drainage layer. The use in the upper of the substrate is dangerous because it can provoke fungus diseases due to the high humidity. It is easy to use and have an excellent capacity of retain humidity however it decomposes very fast specially when the plant is often fertilizer (like Phalaenopsis, por instance) making difficult to keep it alive.
It must be used indoors to provide a controlled watering. If it crumbles, you must renew it.
Osmunda fiber: Very used for the American and European growers, it never (or very rarely) used among us. It has good aeration properties and breaks up slowly however it tends to arise when watered.
Wood log is very easy to use. Just tie the plant around the log. The plants will never suffer for being too much wet. It is not recommend for dry climates because it doesn't retain water.
Tree fern found in stick, slab, containers, fibers, is the most known and the most used substrate in Brazil. It hold well the plant and gives the nutrients while decomposing. It is a very good substrate but in high humidity climate, it can suffer fungus attack.
To get best results, just used the fiber, previously sifted in order to eliminate the dust which can provoke rots when is decomposing. Never use tree fern dust. It must be renewed after 2 or 3 years, depending on the plant.
Cabbage-palm and Peach-stone, they must be boiled before using to inhibit budding. The decomposition is very fast and must be renewed, at least, every 2 years.
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