POTTING MEDIA

Most orchids are epiphytes. ORCHIDS WILL NOT GROW IN REGULAR POTTING SOIL!

I offer this warning because years ago, when I was first learning about orchids, I nearly killed a beautiful and large plant given to my wife (then girlfriend) as a gift by a friend. Fortunately, she still married me, even though I repotted her giant Oncidium into a dense pot of garden soil... and consequently reduced it from a couple dozen large and healthy psuedobulbs to two spindly little new growths that barely managed to survive solely because they weren't in contact with the dirt. I was trying to be helpful, but in my ignorance doomed the plant to a miserable setback (it has since recovered, after pouting for several years, but still has not yet returned to its former glory).

Epiphytes (which literally means "upon the leaf") are sometimes commonly known as "air plants." They grow on the branches of trees in the rainforest. The only real purpose of putting any kind of media in their pot is to hold the plant upright, and possibly also to aid a bit in moisture retention between waterings. The main function of the medium, though, is to provide support. Anything that does this and allows good air circulation around the roots is acceptable as a potting media.

Each type of media has its own advantages and disadvantages, and some of these are exacerbated by local growing conditions. The best way to choose a suitable media for your growing area is to speak with local growers and breeders to see what they are using. Common media include the following:

New Zealand sphagnum moss: most often used for orchids that need to stay moist, such as pleurothallids.
peat moss: Used for the same reason as sphagnum.
fir bark chips
redwood bark chips
osmunda fiber
tree fern fiber
coconut fiber
coconut chips
sifted perlite
granular charcoal
expanded clay pellets
cork (usually used as a slab to mount orchids)
rockwool
The size of individual particles in the media affects its water retention character. Small chips of a medium retain more moister than will large chunks of the same medium. All the media listed above dry at different rates. The media at the top of the list retain the most moisture, while those toward the bottom of the list dry out much quicker. If you tend to overwater, think about using the faster drying media. If you prefer to water less, use the media that hold moisture. Many people combine media (at OrchidMania, we typically use a mixture of fir bark, perlite, and charcoal) to suit their watering habits and preferences.

source:orchids.org
photo courtesy of aka fortex