Water in morning vs. evening >60F
 

Watering at night is an issue with Botrytus below around 58F night time temperature, so during the colder periods morning watering is certainly indicated.
But what about the warmer seasons when night time is >60F? Is there an advantage to watering in the evening?
My way of thinking has been, that by watering in morning, the evaporative cooling will help keep peak temperatures in check [I do have "under bench" misters, foggers, and swamp cooler; all with automatic controllers]. An other way of looking at it is that there is longer time for plants to absorb water if watering is during evening.
Both arguments make sense, so either I am missing something, or it does not matter. Anybody with some reasoned opinions?

I grow mainly mounted (70-80%) in pretty good humidity (RH60-80%: without watering), in a small GH and two terraria.

Stomata close at night (or in the dark) as a plant only transpires during the day (or in light) and stomata are part of the transpiration process. if you water them at night the water will still be there in the morning bec the stomates have been closed and no transpiration has occurred. Thats why we are told to water during the mornings is to take full advantage of the water with the light. :twocents:

you have that backwards. the stomata close during the day, and are open at night. the recommendation to water in the mornings is to reduce the possibility of a Botrytis (or other mold) infection, since these types of mold grow best when it is dark & damp.

In summer, I water both in the morning and at night, because of the extremely low humidity here. If you're keeping the humidity between 60-80%, you probably do not need to water more than once per day (if that much). of course, this will vary depending on what types of orchids you are growing.

I am with RJ about this....sunlight, is a key reactant in photosynthesis. Most plants require the stomata to be open during daytime....the air spaces in the leaf are saturated with water vapor, which exits the leaf through the stomata (this is known as transpiration). Therefore, plants gain carbon dioxide by simultaneously losing water vapor; and you need the sun's light and energy to do that.

yet Kip is right in saying that watering at night might attract bacteria and sickness to the plant

backwards hey? Im dissappointed with you kip. your reading comprehension of scientific facts needs improvement :twocents:

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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This is a good question. We had a speaker at our local Orchid Society who remarked on the fact that in Thailand, it rained day and night and that the plants, in a natural setting and in grow-"shelters" were fine. The only difference to the growing conditions here, that he could come up with as perhaps an explanation, was that here grow and green houses are enclosed. So, maybe, if there was strong ventilation or air movement, plants could be watered at night ? We would have to hear from people who have watered regularly at night; probably few and far between as everyone is always "told" to water in the day, and as early as possible.

In his book on bulbos, Bill Thoms, recommends fertilizing in the evening because he says that the plant has a longer period to absorb the fertilizer before it dries. But watering or fertilizing in the morning makes a lot more sense to me. If I water early enough in the morning, the plants stay wet for a reasonable period of time and then dry completely before nightfall to help control fungus. But, if I couldn't fit that into my schedule, I would be perfectly fine with watering in the evening. We need to balance what's best with the plant with what's best for us.

I'm not sure I count all that much but I water exclusively in the evening.

Around 9 - 11 at night.
Sometimes later.

I don't have any orchid beyond a few basics though.

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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.

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

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.

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?

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.:hello

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.:)

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.

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.

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!

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).

I imagine if your cultural conditions preclude the growth of fungi and bacteria when you water is immaterial - as long as your plants get enough water, whenever, they're fine.

However, as most people's cultural conditions are not perfect and fungi and bacteria do sometimes take hold, altering your cultural regime ("make sure everything is dry by night") helps to mitigate that. If you have strong air circulation (be it from fans or natural wind), drying tends to happen fairly quickly no matter when you water.

Watering is perhaps the single most variable aspect of orchid culture; what works for one person may completely wreck another person's plants, so even if someone conducted a large growth trial, unless you were replicating conditions of temperature, humidity and airflow, plant species, fertiliser regime, light and medium, (and possibly other less obvious factors) following that regime (if successful) may not be all that successful in your conditions and for your motley crew of plants. Very few people would want to grow a large monoculture of a particular variety of orchid in an expensive environmentally controlled growing area.

Depending on the season, I sometimes water several times in the day, sometimes in the early evening; this is only when it is very hot and dry however. In the winter, I am cautious to water only earlier on.

Another thing to consider in winter besides disease is cold; wet leaves will undergo some degree of evaporative cooling; if your conditions are borderline "too cold" for more sensitive tropical species/hybrids, you may push them over the edge into cold damage. This is less likely during the day, as temperatures tend to be higher.

We also tend not to keep monocultures of the same plant, so even within one collection the "right" culture varies from plant to plant; when you have to cater to everyone, you usually end up catering to the most difficult or sensitive!

Experience has generally shown that "early watering" is on the whole the most effective strategy for most people. As with most things, YMMV!

Completely non-scientifically I avoid watering after 12pm in the winter, but will water in the evenings during warm weather though still try and get it done in the mornings if possible.

I have sometimes had a problem with an already stressed plant getting rot after water has accidentally been left on the leaves but that can happen morning or night if it's not warm enough for it to evaporate quickly.

I've also found that a plant like Bulbophylum will rot very quickly if water is left on it. Again this can be morning or night but as water dries slower when it's cooler in the winter it's more likely at night when I keep the house cooler.

Just my unscientific observations :twocents:

Terquem and Lecoufle state that erwinia and other fungal ailments in orchids are primarily transmitted plant to plant via water droplets laying on the plant at cool temps. They suggest keeping the media as dry as possible to help prevent root rot also caused by wet conditions especially at cool temps. Bertsch cautions that Botrytis, a non specific fungus, developes in water droplets left on leaves overnight. Have been reading the same for years in mags and books. Light turns on blue light receptors in guard cell membranes. This stimulates proton pumps, causing absorption of potassium ions, increasing turgor and causing stomata to open. In the light photosynthesis occurs depleting CO2 inside the leaf causing the stomata to open. Certain environmental stresses, drought, high temps, wind, that cause water depletion will lead to daytime stomata closing.

Orchids, and other plants, in the wild get quite wet in the early morning. those morning dews.

I think as long as there is enough air movement, plants do not get diseases.

I seldom water my plants at night, but when I do, I only pour water in the pots not spraying water on the entire plants.
I just don't want to take any chance.

Here in Costa Rica, at present the rainy season begins with a daily schedule at 3 PM and lasts most of the night. This also gives us a heavy mist and lower temperatures and is expected to last until possibly November. So, this really means that the orchids here in the wild or growing outdoors are subjected to a major water dominating habitat and most of them appear to do very well. To me, this defies all my earlier conviction about early morning watering schedules that had to be faithfully followed.

But what are the temps at night where orchids grow? And how much breeze is there? A good breeze will quickly dry out the water sitting on the foliage and any temps above 65*f will inhibit most fungal problems.