If you want a simple key to Dendrobium care, here it is. Look at the thickness of the roots. A good deal of the Dendrobiums have very fine roots, kind of like an Oncidiums root system. They need a finer mix that retains a bit more water. They however do like to be watered quite so often as an Oncidium.
Dendrobiums like the Phalaenopsis types possess coarser roots similar to many Cattleyas, they like a more open mix with larger particle size.
A good way to go is for the fine rooted ones, try a "seedling mix". For the heavier roots, try more of a Cattleya mix.
If you want to mount them, in my experience, they do not like it as much as a pot. For me they show signs of being underwatered 6 months after being mounted. I have had much more success mounting the Phalaenopsis types!
Suggestion #2: place them in as small a pot as possible, underpot them. The nigro-hirsute plants I grow are 15, 18, even 24 inches tall, yet they are in no more then a 4" pot. They look a little 'silly' if you will but They Are Happy that way!!
And as a last suggestion, repot them as infrequently as possible. Bark breaks down often forcing repotting, aliflor does not. They can grow undisturbed for longer periods of time.
My final word: with very few exceptions, they might not like as much light as we imagine. Try dialing down the light intensity a bit. Five hours of 3,000 foot candles is harsher then 7 hours of 2,500 foot candles. They will flower either way but look and grow better with the lower light intensity.
