Bark

This is the evenly broken pieces of the bark of the fir tree. The bark is taken from the white fir (Abies concolor), red fir (Abies magnifolia ), both of which are from California and also from Douglas fir (Pseudostuga aneuzeiesia) which is from the Pacific North West . Bark of the Ponderosa pine (Pinus ponderosa )is also sometimes used , mixed with fir bark in the ration 1: 4 . Fir bark may be used as such or mixed with redwood bark in the ration 3:1 . When mixed with redwood bark , chances of attacks by fungus , snails etc. are considerably reduced . It is also used in combination with free fern fibre. Though most of the conifers are temperate plants , they do well in the cooler hill of the tropic also .

Bark also needs fertilising , which could be supplied in liquid form at regular intervals or with every other watering , or added in solid form prior to potting . To one cubic yard of bark , the following may be added :

5lb of hoof and horn meal

1 lb of single superphosphate

4 lb of calcium carbonate

4 lb of dolomite lime ( Jones , 1964)

Bark is available in several different grades , from fine to coarse , to suit the requirements of orchids of different sizes and age. It was introduced in 1955 and immediately became popular . It is reported that more than 90 % of American Orchid -growers now use bark.

Osmunda and tree fern fibre are self-conditioning , ie. they are able to maintain thier own pH , whatever be the composition of the water of the fertilisers we add to them . But bark does not possess this quality and hence , whenever bark is used , the pH of the medium should be checked frequently , and corrected .

Apart from these popular types of media , namely , Osmunda , tree ferns fibre and bark, orchids have been grown experimentally in a variety of media and results reported -perlite (plastic pellets ), coconut fibre, charcoal , broken bricks , moss , gravel , peat , pacco wool , saw -dust , wood shrivers used for packing purposes, oil-palm-seed husks and several more have been tried individually and in combination with other media .

Osmunda and tree ferns are available in India in the interior of the forests , though on the Western Ghats they are not abundant . In this age of intensified deforestation , it would be advisable not to tamper with what little wealth we have in this botanically interesting specimens. Bark industry is non- existent in India , no doubt , due to lack of demand for the product. But it has potentialities , particularly in view of the increasing interest evinced in orchids and their culture in recent years in this country. Selection of a suitable treebark is the first prerequisite . During our survey of the forests of Western Ghats we have very often observed that orchids show preference to certain kinds of trees while they totally avoid certain others . For example , the smaller kinds of species like Polystachya , Oberonia , Chiloschista , smaller Dendrobiums etc appeared to have a special preference to Careya arborea , while the larger species especially Vanda tessellata and Acampe praemorsa inhabited Mango , Jack and Tamarind trees in great masses.

We found a satisfactory medium in coconut husk which is available in plenty in south India and is very cheap. The husks were cut into small pieces, the size chosen depending upon the size of the orchid to be potted , the smaller and more delicate ones requiring finer grades and the sturdier ones, coarser grades . The pieces are washed throughly , dried in the sun and stored . Orchids prefer dry husks to the raw green ones . The dried chips were mixed in equal proportions with broken pieces of clean roofing tiles which helped not only in retaining moisture , but also in adding weight to the potting medium thereby keeping the freshly potted plant in place . Usually for terrestrials like Calanthe ,Acanthephippium , the various Habenarias, Arundina etc. the following compost was used successfully: