Hello, TZ!

Not that I doubt you, but I'd be interested in finding any
empirical data that indicate that there is substantial foliar uptake in
orchids- CAM or otherwise. I know there was one paper (Sheehan?) that was
in one of the Orchid Biology books (book 2 or 3) that used radioactive
tracers to show this was the case. Reportedly, the author recanted his
results some years later, indicating it was probably contamination.

In any event, I'd like to know of any papers on the subject. I've
always thought the cuticle of orchids is too thick for substantial uptake
of nutrients via the foliar route.

I do have an anecdote to share with the group: some orchids do not
like foliar feeding. I have noticed that bacterial infections (apparently
anthracnose) form more readily when water with fertilizer gets onto the
leaves, even when given time to evaporate. I suspect, but have no
evidence, that it supports bacterial growth which in turn may facilitate
infection.

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-AJHicks
Chandler, AZ