Water in morning vs. evening >60F

[lambelkip]

Originally Posted by Ray

In CAM plants (some, but not all orchids), the stomata are only open at night, as that is when the relative humidity is naturally higher. It is an evolutionary adaptation intended to conserve water.


Ray Barkalow
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My mistake, I thought most orchids were CAM.

Every orchid book I've read that recommended watering in the morning explained that it was to prevent rot.

However, I've never heard of any scientific study showing any benefit to either watering time. If you're willing to try it out, and it works for you, let us know.

[gnathaniel]

Originally Posted by lambelkip

My mistake, I thought most orchids were CAM.

Every orchid book I've read that recommended watering in the morning explained that it was to prevent rot.

However, I've never heard of any scientific study showing any benefit to either watering time. If you're willing to try it out, and it works for you, let us know.

I think you're more right than not, Kip... From what I've read it's estimated that at least 60% of all orchid species use CAM to some extent, and AFAICT most though not all of the commonly-cultivated species/hybrids fall into this group: Laeliinae, Vandeae (incl. Phals, Angraecoids, etc.), many Pleurothallids, many or most Dendrobes/Erias/Bulbos, and many or most Oncidiinae/Maxillareae. Most epiphytes or lithophytes of any genus experience enough moisture variation throughout the year that they've evolved capacity for facultative and/or 'weak', if not necessarily obligate 'strong' CAM.

Besides, even if an orchid is an obligate C3-metabolizer doesn't mean it closes all stomata at night; not all C3 plants exhibit complete stomatal closure at all times. Most plants vary stomatal opening and closing in response to environmental conditions beyond just day/night. Also, many CAM-users are facultative, using water-efficient CAM as needed and the more energetically-efficient C3 as daily or seasonal conditions allow. I found a recent paper describing an Oncidium (previously considered obligate C3) in which the roots and pseudobulbs, though not the leaves, switched to CAM when drought-stressed. So actual plant metabolic strategies are a lot more variable than just C3="stomata open during the day" and CAM="stomata open at night", but regardless I can't agree with RJ's contention about diurnal stomatal cycles, especially WRT orchids more of which can use CAM than can't...

tl;dr--most orchids we grow are unlikely to have all stomata closed at night

[gladwrap]

Hello I am a newbie to this forum, this is the first post but I am confused already,do you water day or night,I have aussie natives and have always watered before lunch so they are dry before dark especially cold wet nights

Please go easy on me.

[isurus79]

Originally Posted by gladwrap

Hello I am a newbie to this forum, this is the first post but I am confused already,do you water day or night,I have aussie natives and have always watered before lunch so they are dry before dark especially cold wet nights

Please go easy on me.

Having orchids dry by night always works on cold nights, no matter whether they are CAM plants or not.

[gladwrap]

Originally Posted by isurus79

Having orchids dry by night always works on cold nights, no matter whether they are CAM plants or not.

Thanks for the reply isurus79,I think I was on the right track.