Orchids are traditionally divided into two principal categories, epiphytal and terrestrial. Epiphytal orchids grow on the bark of tree trunks and tree branches. There are several different methods for growing this type of orchid in one's house or in a greenhouse. It all starts with potting.
Epiphytal orchids, in their natural habitats, have their roots more exposed to air than the majority of other plants do. As a consquence, by "potting" we do not mean to pack them all around with dense potting soil. Rather, we want to place them in a pot containing loose, organic matter, from which they can pull necessary nutrients, along with rocks or broken pottery pieces to create sufficient open space as well as to assist the plants to stay upright.
The standard recipe for potting matter suitable to epiphytal orchids is 1 part sphagnum moss to one part peat. Place a layer of this matter in the bottom of your pot, followed by a layer of rocks or pottery bits, then another layer of the compost, and so forth. When the pot is around a quarter or at most a third full, carefully place your orchid's root system down into it. Then proceed to add more rocks and mix, packing all of this material just tightly enough to support the orchid plant.
You should gradually build up the compost until it is up to and even a little above the top of the pot. The height you should go above the pot depends on the size of the pot as well as the depth to which you have placed the orchid. The general rule is to allow the plant's crown to rest on top of the compost. By crown is meant that part of the plant from where the roots start.
If you happen to be repotting an orchid, you must take care when extricating it from the old pot. If there are any young roots clinging to the exterior of the pot, you should try to ease them off with a penknife. It you have a mass of living roots -- meaning, roots that have sap in them -- attached to the interior of the pot, then you might need to break the pot and pick away all of those roots that you can. You may need to repot it with pieces of the old pot still dangling from the roots, and this is OK.
It is good not to water the orchid for a day or so before and after potting it.
This has been a basic introduction to potting epiphytal type orchids. The subject can be more complex than this, especially in the case of some of the more delicate or senstive species. Whole volumes have been written on how to pot the various types of orchid! Happily, most of us don't need books devoted entirely to the potting art in order to enjoy success with orchids. A recognized, comprehensive guide to all aspects of orchid growing is sufficient.
In our day, of course, we have a tremendous amount of solid information on the successful way to grow orchids. The most accurate and clear guide to modern orchid cultivation, it is widely acknowedged, is Orchid Care Expert by Nigel Howard, which may be downloaded online. Howard's well-written guide constitutes a complete education all by itself. And, you will find it appropriate for beginners as well as more experienced orchid cultivators. Also, visit the Orchid Secrets site, which contains a growing database of information on a wide range of facets of orchid care.
