I believe the idea is that the guard cells of the stomata allow for uptake
in foliar feeding. At least that's what Alan Koch says, and he quotes alot
from Marschner too.

As to the idea that stomata close during the day and open at night there is
a broad time zone most notable in the early AM when orchid growers (Rebecca
Northen being one) notice the increase benefit of early AM sun - even
direct sun - on their orchids. One of the reasons for that being that the
stomata are still open becasue its not yet hot. So fertilizing can be best
taken up by the plant at those times. Both by the roots and the leaves
(the 'leaf' part is my surmise)

As I get older I'm beginning to wonder about the foliar feeding & cuticle
inhibition thereof idea. I understood that everyone quotes from one study
and that may never have been reproduced. So I'm willing to listen and read
any cites.

K Barrett


"TZ" wrote in message
om...
Hi AJ,

If I knew of any empirical data for orchids I have forgotten it. I
would assume that what goes for thin leaved, thin cuticle crop plants
would hold for orchids with a similar leaf morphology. I would not
expect a Cattleya or Phal to get much out of it unless the liquid went
down into the crown and came into contact with the softer developing
tissue (which is what could use the nutrients the most).



I gleaned the info out of either

Mineral Nutrition of Higher Plants. 2nd Ed. H. Marschner, 1995.

Physiochemical and Environmental Plant Physiology, Park S. Nobel
or
The Physiology of Tropical Orchids in Relation to the Industry, Hew
and Yong


Hew and Yong have the graphs of Phal CO2 levels over a day but do not
discuss it in relation to stomata, only water stress.


The whole debate about foliar fertilizing seems academic for hobby
growers. If you are growing in a greenhouse the leaves are gong to
get fertilizer splashed on them anyway, and if you are growing in a
windowsill many factors other than fertilizer are probably limiting
growth.

I rather protect the leaves/plant from infection by keeping them dry
than possibly get a little bit more growth from foliar fertilization.






(Aaron Hicks) wrote in message
...
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.

The address in the header is a spam trap. Send no email there.

-AJHicks
Chandler, AZ