Choose a potting material which will not decompose quickly. For us Pine Bark have given great results and it is recommended potting medium by American Orchid Society (AOS). This mixture allows two-three years to lapse between re-potting efforts. Coconut Husk or the mix of coconut husk and charcoal also works. But coconut husk decomposes quickly, especially at the bottom of the pot, which increases the chances of root rot and fungal/bacterial infections. We wouldn't suggest using charcoal as a potting medium unless it is mixed with coconut husk.