Water in morning vs. evening >60F

[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

[isurus79]

Interesting thread. I'm guessing that its just safe to assume that the epiphytes are CAM then? I always assumed most of them were anyway! lol

As for the original question about watering day vs. night in warm temps, I don't think it matters. When I lived in Hawaii I'd water whenever it was convenient. Here in Texas, all my plants get hit 1-2x per day (again, whenever convenient) when they are in the summer heat and I've had no ill effects. They also grow quite well no matter when I've given water. Cool weather is a different story, but clearly not the original question.

[tropterrarium]

Thanks for all the replies. Interesting consideration with C3 vs. C4 vs. CAM. We'll shortly have a talk about CAM at a local OS, so should be illuminating.
Re open stomata, type of metabolism is one thing, availability of water, nutrients, growth stage, temperature and humidity are complicating factors.

This whole thing got started by a speaker from a extremely well-known vendor, who made the point of evening watering above 58-60F. So just wondered what the rest of the community thinks about that.

I mainly grow medium to low light plants (pleurothallids, Oberonia, Stigmatostalix, Ornithocephalus), no vandas or cane dendrobiums. I emphasized the mounted aspect, because the medium (or rather lack thereof) has lower to no water holding capacity.

Thus far, consensus seems to be, that it does not matter much, though could be an interesting study question. Maybe an AOS RFP?

[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.

[pipsxlch]

I don't have the training to weigh in on the timing of the stomata opening. I grow exclusively outside however, so during the wet season most if not all my watering is done by nature. Our typical summer pattern is daily to 2-3x weekly thunderstorms in the late afternoon. Things have rarely dried out by dark; the humidity even on a rain-free day is high. Nightime temps are usually 70sF. My plants seem to be happy with this.
In the cooler/drier winter months, I try to get my watering done no later than early afternoon, preferably morning. When things have stayed cold and wet is when I've seen problems.

[james mickelso]

I water in the evening during the week as I go to work too early to water. But I thoroughly water everything on the weekends. What I water in the evening are all my small potted and mounted orchids. I haven't found any difference. But from all I have read in the hundreds of AOS mags and tons of books says water as early in the morning as practical mainly for fungus and mold prevention. As for stomata it doesn't matter. To a point that is. I know there are some nit pickers here whom I love to read their take on things.

[jeremyinsf]

I'm with James. I'm also pretty careful about not leaving water on the leaves/crown/flowers etc. I'd rather water in the evening than not water at all!

[naoki]

James, here is a nit-picker's comment. I think stomata opening plays one of the most important roles in water uptake (and some nutrient movement). Water uptake by is all passive process, and water follows the gradient of water potential, and it flows from roots to leaves via xylem. David Attenborough's 'The Private Life of Plants' explains this tension cohesion theory in a simple way.

Nat's comment about facultive CAM makes sense for plants with rainy and dry seasons. I didn't know that leaves and roots have different strategy, though. C3 process is always more efficient if water usage can be ignored.

I personally don't know why those books say that the water shouldn't be on the leaves at night. Plants which are stressed or injured could be susceptible, but for healthy plants, lots of people don't have issues (Japanese orchid book indeed recommend watering at night, which is more natural for SOME species). Imitating 'nature' is a good start, but it may not be optimal under highly artificial environment. I guess it probably doesn't matter either way (morning or evening watering).