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Why Bark for Orchid Culture ?
To fully understand the answer to this question one must first understand a fungus - plant relationship called "mycorrhiza association" , mycorrhiza is a nutritional relationship between certain fungi and the roots of plants including orchids. Orchids that are saprophytic depend almost entirely on this relationship for their nutrition while others have no real need for this relationship at all.
Mycelium's are fungal strands - endotrophic mycelium's grow within the plant whereas ectotrophic mycelium covers the roots or tubers externally but do not enter it. There are two different types of endotrophic mycelium's relevant to orchid plants:
(i) Tolypophagy where the fungal coils of the mycelium enters the roots and are killed and digested by the plant.
(ii) Ptyophagy where only the tips of the fungus enter the digestive cells of the orchid roots and the fungal mycelia's contents are squirted into the digestive cells of the orchid plant.
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Whether the fungus receives carbohydrates or other useful nutrients in return from the orchid for supplying these inorganic nutrients to the orchid seems hard to discover. It is known however, that the fungal mycelium consists of protein, carbohydrates and oil, so when this is digested by the orchid plant more than just inorganic nutrients are obtained.
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So why treat bark?
It is known that not all forest trees support orchid growth. Some trees can support populations of orchids while an adjacent tree can be devoid of any orchid plants. It is however, known that some barks exude phenolic substances such as tannic, elegiac and gallic acids and these are suspected of being toxic to orchid seed and the growth of the orchid plant. It is more likely however, that these phenolic substances are inhibitory to the growth of fungi particularly the mycelium fungi.
The reason therefore for treating bark prior to its use is:-
(i) To remove any of these phenolic substances that maybe present.
(ii) To feed the micro-organisms present and commence a healthy growth of mycelium fungus to live with the orchid from the time of re-potting.
(iii) To leave within the bark structure traces of nutrients such as iron, phosphorus and magnesium in a soluble form that the plant can take up as it grows.
(iv) To correct the pH to the ideal range for orchid culture.
These mycelium fungi are "Good fungi" and have no connection with the pathogen that causes the form of the bacterial pneumonia known as "legionnaires Disease".
Orchid Barks can be purchased from Fame Orchids Nursery direct. Various grades are available in 50, 25, 12.5 or 2 litre bags.
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Happy Growing
