Plants are traditionally grown in soil. Many have experimented in using medium other than soil to grow healthier plants. You may have heard about hydroponics and tissue culture techniques. Depending upon specific needs of individual plant, micro-and macro nutrients are added to the medium to supplement nutritional requirements. These are costly of techniques, so majority of us resort to the natural ways of growth and propagation. For orchids, we can use a variety of natural organic or inorganic growth medium. In the market a number of man-made artificial mediums are also available. You can even use your own ingenuity while choosing the right growth medium for your orchids. You only need to keep in mind three things: the medium should be able to retain some moisture, but it should not remain wet for long (no water logging!) and it should be porous enough to allow free circulation of air.
My orchids mostly fall in the epiphytic category, so I have used coconut husk as well as coconut shell for many of my orchids. When using coconut husk, I separated the fibers into smaller sections. Then I tied these with the orchid in such a way that the roots were covered with the husk. This can now be hung as such or can be tied to pieces of broken off or fallen tree branches (thatís what I used!) or logs (about 20-30 cm long and 4-5 cm wide).
Wooden slabs with grooves on the surface can be used to hang orchids. Grooves in the slab helps the orchid roots in binding to the wooden surface. Advantage of using slabs is that, you can use the dipping method watering the orchids. In this method, the orchid is dipped in the water container and then removed after about ten minutes or so, giving roots the time to absorb water.(Caution: Avoid splashing water on parts other than roots).
Moss also retains moisture, so it can also be used as growth medium for epiphytic orchids. For terrestrial, you can use these as a layering on top of the potting mixture, to prevent evaporation.
Coconut shells can also be used. I have seen orchids growing in tyre-tubes, even other flowering plants. While using rubber tubes, do not forget to drain the excess water, or better still punch a couple of holes in the bottom.
Coconut husk and moss can be hung in wooden or plastic basket; while logs, slabs, coconut shell, tyres tubes can be hung by themselves using coir ropes or plastic/metal wires.
For terrestrial orchids, using garden soil/mud worked fine for my orchids. You can use mud individually or mixture it with bits of charcoal, bark pieces and/or small pebbles etc. My Phaius tankervillaea has been growing in plain mud for last ten years. I have kept it away from direct sunlight, along with the other shade loving plants.
Each orchid has it own specific requirements. So while choosing a growth medium check out the growth needs which are particular to that orchid. There are a number of growth media available in the market, locally or on internet. If you have bought the orchid from a nursery, do not forget to note down all the specific and general needs.
Whatever medium you use, just take care on water logging and make sure that there is some air circulation around the roots. Change the medium occasionally.
In case, you notice fungal growth, remove it immediately and seclude that orchid to prevent spreading.
You are the best judge to decide which medium suits your orchids best. Each orchid behaves differently, so the response to the growth media too could be different, so do not worry if some of your orchids do not grow well in a particular medium. Just change it:-)