The bamboo orchid, or Arundina graminifolia, is a small lavender and white orchid native to Burma. It has become naturalized on the Big Island of Hawaii, but is not invasive. A real estate developer introduced this plant to the southernmost Hawaiian island to enhance the name "Orchid Isle." It was well adapted to the warm, damp climate and has spread to many lowland areas, where it often appears to grow out of solid lava rock.
Like most orchids, the bamboo orchid prefers to grow in rocks or bark instead of true soil. However, the website Garden Exotica states it is possible to grow the bamboo orchid in potting soil mixed with perlite or vermiculite, which will improve drainage. In contrast to this advice, OrchidMania states "orchids will not grow in regular potting soil." All orchids need good air circulation around their roots, and potting soil fails to provide this important need.
If you plant a bamboo orchid in small lava rocks, it will do well. Any type of small rock, such as gravel or pebbles, will suffice as a growing medium for the bamboo orchid. However, because rock retains no moisture, you can combine rocks with another material, such as perlite or peat moss, which will provide your bamboo orchid with a source of moisture without keeping the roots constantly wet. When you add a water-retaining material to rock, you needn't water your bamboo orchid every day.
Bark and Peat Moss
Bamboo orchids will grow well in shredded bark, such as the type sold for growing orchids. This substance is fast draining: it retains enough moisture to keep the orchid's roots moist, but not too wet. Peat moss is another good growing medium for the bamboo orchid. Peat moss retains moisture well, making it a good addition to the bark or rock in which you grow the bamboo orchid.
Other Soil-Like Materials
OrchidMania recommends using the following materials as a growing medium for bamboo and other types of orchids: sphagnum moss, peat moss, tree fern fiber, coconut fiber, coconut chips, sifted perlite, granular charcoal, expanded clay pellets, cork and rockwool. The items at the beginning of this list retain more water than the later items--you can choose the material in which you grow your bamboo orchid based on your watering habits. For example, if you like to water your plant every day, choose expanded clay, cork or rockwool. If you don't always remember to water, choose sphagnum moss or peat moss. .