Soil Preparation and Care
The title is actually a little misleading since orchids don't really live in soil.
In the wild, some cling to the sides of trees, getting support from the bark. These are called epiphytes. Nutrients come from the air and they receive water as it drips down the side or falls from branches above. Others, called lithophytes, cling to rocks. Still others will grow in leaf litter (saprophytes). A final type actually manage to grow in sand, or very sandy soil (the terrestrials).
As with all gardening, 'Nature, to be commanded, must be obeyed'. Here, that means that in order to successfully care for orchids in the home or hothouse, it's important to be aware of the way they've adapted to their natural environment. Then those conditions can be emulated in an artificial setting.
Fortunately, that's very easy to do. Putting together a mixture of lava rock or fir bark chips is simple. Watering should be regular but light. Slight drying in between watering is a good idea with most species. The loosely packed material helps ensure the good drainage that allow orchids to thrive.
Repotting is required about every two to three years for most common orchid species. Like other plants, they can outgrow the size of pot they're in. Also, the media they cling to (like bark) can break down over time due to repeated watering, insect activity and other causes. Left in the pot too long, roots can grow over the side, indicating it's past time to take action.
Fortunately, since the material used to support them is very loose, repotting is much easier than with most plants. It's still necessary, of course, to exercise care. Repotting should be done when the plant is relatively inactive, such as early Spring before the high growth season begins.
Simply remove the plant from the pot and lightly brush off any clinging material from the roots. Clip any excessively dried or soggy roots to prevent any problems from spreading and give the plant an impetus to regenerate new roots.
Refill the pot, a larger one if needed, with a layer of bark chips, lava rock or other media suitable to your species. For some species, a special orchid sphagnum moss does very well. Make a space for the plant and gently insert it, then fill with more material up to the crown (rhizome) just below the level of the rim.
For those needing a little extra help, you can stake it temporarily. But try to avoid leaving it in place permanently. Orchids do best when they can grow freely.
Also, when you place the media, keep in mind that its primary purpose is support, not feeding. Good air flow is essential. Smaller chips will retain more moisture and provide less air space. Size according to your species' needs. Then, once you notice new leaf growth, feed with a bit of fertilizer (18-18-18).
