Guidelines for Growing Mounted Orchids:
Many genera and species grow well mounted ...after all, there are no pots in nature! Types that typically respond well to slab culture are those with thicker leathery leaves and prominent pseudobulbs.
Slab culture of Orchids do tend to require more time and attention than pot culture - but only in the respect that they dry faster. However, the benefits can be great. Mounted plants rarely need "repotting" - which means far more time growing and less time re-establishing from being disturbed. Sometimes, growing a plant mounted makes them easier to manage - particularly true if a plant is sensitive to being overwatered and/or wet roots.
Plants can be mounted on any neutral substance. Commonly used materials are: aged wood, various barks, cork, cypress & tree -fern. A "bedding" of moss, sphagnum, osmunda, husky fiber, or oasis (the material florists stick flowers into), all of these provide a moist pad so the roots have a longer time to absorb water. Dehydration is the most common cause of decline in slabbed/mounted plants. It is the result of low atmospheric humidity and too infrequent waterings. Many people try to get by with watering once a week, a practice common to pot culture, but wholly insufficient for plant whose roots are so much more exposed to the air. If you do not have the time for daily watering of slabs, an alternative is to soak them (plant, slab and all ~ just don't forget and leave them to drown!) in water for 10 to 20 minutes three times a week and use misting for the in-between days. Using a very weak fertilizer solution is also helpful.