Over the years of orchid cultivation there have been many different ideas on what to grow the orchids in. Still today there is a wide range of composts from which to choose, both those that can be bought ready-mixed and those that can be mixed at home from a variety of ingredients. For the beginner this can be a little confusing, so it is best to keep it simple.
There are several different grades of bark that can be used for different types or sizes of orchid. The finest grade contains pieces of bark that are, on average, 5 mm (1/4 in) across and this is ideal for very young orchid seedlings or mature miniature orchids that have a fine root system. As the young plants mature and are moved into larger pots, they can be potted into a coarser grade of bark; each piece in this grade measures around 2 cm (3/4 in). Certain types of orchid prefer an even coarser mix, such as cattleyas, which like to be kept relatively dry-bark with quite large chunks will not hold the water for as long as the finer grades.
Try to buy bark chippings that have been produced especially for orchids. The bark that is sold for mulching flower beds in the garden can be very rough and contains a lot of white sap wood pieces which are not easy to use in a pot and do not hold moisture well. An even grade with bark pieces of a similar size is the best. The most commonly used barks are pine and fir, which are stripped in timber production. Redwood barks are of a higher quality, so tend to be a little more expensive.
There are many additives that can be used in conjunction with the bark to aid either moisture retention or drainage. Moss peat or a peat substitute will help to prevent the compost drying out by holding water. This is good for those orchids that prefer to be relatively moist, such as the terrestrial paphiopedilums and pleiones. It is also common to add perlite or the larger perlag into a peat and bark mix, as this helps with the drainage. These are types of porous volcanic rock that have been reduced to very small granules. A mixture of peat fine-grade bark and perlite is ideal for seedlings.
Before bark composts were so easily available, the most common potting mixes were made from sphagnum moss and osmunda fern fibre. The latter is not so easily obtainable now, and bear in mind that it dries out easily. Sphagnum moss is still regularly used, usually purchased in dried and comparted form, which is then rehydrated with Inter. The moss helps by holding moisture around the orchids’ roots and is especially good for potting sickly plants to aid recovery. Another possible addition to compost mixes chunks of coconut fibre. This performs a similar role to the bark in holding some moisture while still draining freely.
