Afternoon watering... a disconnect

[paphioboy]

It can rain continuously all night (after 5pm, through to morning) during the year-end monsoon period in Malaysia and some South-Eastern Asian countries. I think there is no reason for wild plants to NOT rot. I have bulbos in my collection who turn a black leaf or two after a really heavy downpour and some thinner-leaved species (Gongora) develop some black spotting, which I think is pretty normal for outdoor growing. You can NEVER have perfectly unblemished plants, wild or cultivated, if growing exposed to the elements. I suppose plants grown outdoors make up for the damage by extra vigour in the new season's growth. For example, bulbos grown outdoors in the tropics can complete 3-4 growth cycles in a year, but if grown in greenhouses, I think the growth cycle will be slower..

 

[gonewild]

Lance that was the point that started this thread.

How come only "serious problems" happen in GH when watering at night, but jungle plants survive (barring some "mechanical damage")?

Because in the jungle plants are allowed to grow naturally. What I mean by that is how they grow in regards to gravity relating to the orientation of the leaf axils. The most problematic types as far as "wet at night" problems are types like phals and paphs that have crowns that trap water. In nature the plants grow in such a way that the crowns can drain. perhaps on the trunk of a tree and the crown points downward. When growing on benches this does not work so we tend to stake plants upright so they are nice and straight. This "forced" upright orientation creates a water trap that DOES lead to rot problems. Grow your plants with the foliage able to shed water and the problem goes away.

Orchids have survived in jungles for millions of years getting rained on at all hours of the day, but the way individuals talk (such as "contributes to serious problems") suggest that you can loose a whole GH of orchids in a week by night watering.

You can loose a whole GH of Phals in a week if you allow water to sit in the crowns at night. I'm not saying it always happens but it can, will and does happen. Now bear in mind in talking about plants growing upright in pots on benches.

I have a fogger set to a humidistat in my GH that generates considerable fog whenever the humidity drops below 70%. I know it comes on at night at times because I've been in the GH at all hours checking things out. But over the last 10+ years I've never had any all out epidemics. And since going K-lite I'm having very much fewer individual plant problems.

Foggers running during periods of low humidity is a different situation from water wet foliage left from late afternoon or night irrigation. If water is standing on the foliage it is usually because the humidity is high.
It is not high humidity or the water that causes the "rot", it is because the "wet" spots create a micro environment that incubates the rot causing pathogens. By growing your plants in baskets you are likely allowing more the foliage to drain and shed off water and that is a big difference from the standard.
Obviously K-lite has given the plants more resistance to the pathogens based on your observations.

 

[gonewild]

I think what Lance was saying is that there are no actual benefits from watering the greenhouse at night but plenty of potential problems.

That is exactly what I was saying.

 

[gonewild]

Let me also back up here. I see "at night" being tossed around. I'm talking about watering between 3-5 PM, when most rainstorms fire off in the Maritime Continent.

If I water during the morning and have plenty of air exchange, the plants dry out. A lot of people consider that ideal, I don't based on what I've seen in the wild for species like bulbos. Leaves maybe, but not roots.

When I refer to "night watering" I'm refering to having the foliage wet with potential water collected in the crowns when the environment has switched to nighttime conditions.

I like to keep the foliage wet all day but try to have it just getting dry by nightfall.

Watering at night is probably less of a problem than having the crowns full of water that has been sitting stagnant for hours from earlier waterings.

 

[Rick]

Would you agree that "contributes to serious problems" is quite a bit different in magnitude to "can potentially cause problems"?

I agree that most of us would find it cumbersome to water at night to make a practice out of it. And I also wouldn't it make it a practice myself. But I don't think it makes a difference if you water early AM or late afternoon either if you have healthy plants to start with.

 

[Rick]

It is not high humidity or the water that causes the "rot",

I agree with this too, but Helger Perner, is his newest AOS article blames high night humidity as a cause of rot in paph seedlings.

 

[Lanmark]

One reason not mentioned is that orchids in the rainforest are not growing in pots or mounted on "unnatural media". Another is that it does not seem to benefit the plants to water them at night when growing under artificial conditions and it can contribute to serious problems.

Would you agree that "contributes to serious problems" is quite a bit different in magnitude to "can potentially cause problems"?

I'd agree that "contributes to serious problems" is quite a bit different in magnitude to "can contribute to serious problems" which is not all that different from "can potentially cause problems"

:wink:

 

[cnycharles]

one point about plants outside, getting hours and hours of rain and not rotting; usually the problem is having too much water that has no oxygen in it, and having standing water on leaf tissues that allows fungi to settle, and germinate. many or most fungi need high humidity or standing moisture to 'pop'; running water washes away most plant fungi spores. if the spore is not stable where there is not water, then it won't germinate (a relative description, there are likely some fungi that may need moving water to germinate.

water without air (the balance) can lead to lots of problems. plants in the greenhouse that have continually dripping water from a roof or hose leak often are larger than those around that are not getting the moving water that has oxygen in it, and the plant is constantly wet and the media saturated. often our books that have cultural info are written for northern, north american growers who have cool conditions and little air movement for a greater portion of the year, so generalizations get made as to what is the best 'culture' for home orchids. I think it was a few weeks ago someone was posting here that they watered all of their mounted orchids in the early evening, just like was happening in the wild in their neighborhood, and their plants were doing much better than when they were watering them early, or in the morning

 

[Lanmark]

often our books that have cultural info are written for northern, north american growers who have cool conditions and little air movement for a greater portion of the year, so generalizations get made as to what is the best 'culture' for home orchids. I think it was a few weeks ago someone was posting here that they watered all of their mounted orchids in the early evening, just like was happening in the wild in their neighborhood, and their plants were doing much better than when they were watering them early, or in the morning

Exactly!

There are many generalized guidelines to successful orchid culture including those which recommend only morningtime watering routines.These are not unbreakable commandments. They are suggestions based upon years of collective experience. It's always wonderful to hear from those who find success using alternate methods of cultivation, and these successes further broaden our collective base of knowledge.

 

[gonewild]

Would you agree that "contributes to serious problems" is quite a bit different in magnitude to "can potentially cause problems"?

Yes I would agree with that. But the meaning and magnitude changes with what words are used before each phrase.
If you are referring to what I said, I think what I wrote was "it can contribute to serious problems" rather than "contributes to serious problems". In that case the "it can" lessens the magnitude.

I agree that most of us would find it cumbersome to water at night to make a practice out of it. And I also wouldn't it make it a practice myself. But I don't think it makes a difference if you water early AM or late afternoon either if you have healthy plants to start with.

You are correct it does not make a difference and in fact as I have said before I like to water all day long. The main point is to try to avoid wet foliage at night as a precaution to avoid problems. A few years back i had a lathe house in Peru with about 400 plants planted in baskets and I installed a mist system that came on every hour for one minute 24 hours per day every day. This was a mist and not fog, the foliage was wet all the time at night. Never a plant rotted in several years time. But I would not do that in a closed environment.

 

[gonewild]

one point about plants outside, getting hours and hours of rain and not rotting; usually the problem is having too much water that has no oxygen in it, and having standing water on leaf tissues that allows fungi to settle, and germinate.

Yes and when you do have wet foliage with standing water that is low in oxygen if you circulate air over the water the water will absorb oxygen. As you said the increase in oxygen content of the water inhibits pathogen growth. That is one reason to support the need for strong air movement in a greenhouse.

 

[Lanmark]

Yes I would agree with that. But the meaning and magnitude changes with what words are used before each phrase.
If you are referring to what I said, I think what I wrote was "it can contribute to serious problems" rather than "contributes to serious problems". In that case the "it can" lessens the magnitude.

:wink: ...as I pointed out earlier.

 

[Ray]

An interesting thread, but we might also consider that "in the greenhouse" we have a fine little incubator for all sorts of pathogens, while limiting the natural enemies to them that occur abundantly in the wild.

Holger's comment that high humidity in the greenhouse increases the chance of rots might be more related that that than anything else, as by increasing the humidity, we may be improving the conditions for the pathogens.

 

[Ray]

Yes and when you do have wet foliage with standing water that is low in oxygen if you circulate air over the water the water will absorb oxygen. As you said the increase in oxygen content of the water inhibits pathogen growth. That is one reason to support the need for strong air movement in a greenhouse.

Huh? (Sorry Lance, I have to disagree)

Gases have an equilibrium solubility in water that is determined by their concentration in the atmosphere surrounding the water, the temperature and pressure. That equilibrium concentration is reached pretty much instantly, even in water that has been intentionally "out-gassed" (and our irrigation water supplies are hardly that), especially with the surface-to-volume ratios involved.

Air movement does not change any part of the equilibrium conditions, so will not increase the oxygen content of the water.

 

[gonewild]

Huh? (Sorry Lance, I have to disagree)

Gases have an equilibrium solubility in water that is determined by their concentration in the atmosphere surrounding the water, the temperature and pressure. That equilibrium concentration is reached pretty much instantly, even in water that has been intentionally "out-gassed" (and our irrigation water supplies are hardly that), especially with the surface-to-volume ratios involved.

Air movement does not change any part of the equilibrium conditions, so will not increase the oxygen content of the water.

You could be right but I based the idea on what happens in a lake of pond when air moves across the surface. When air moves over water surface of a lake the oxygen level is greatly increased. The main reason is because the air currents makes ripples in the water and the surface increases to absorb more oxygen. Maybe the air movement does not effect small bodies (drops) of water of in the same way? But it probably does. As well when you refresh the air in contact with the wet leaf you are bringing in air that has a slightly higher oxygen content and as such the water would take a little more oxygen to try to stay in equilibrium. Anyway that is what I'm thinking at the moment.

When water evaporates what happens to the oxygen content of the remaining water?

 

[ChrisFL]

You could be right but I based the idea on what happens in a lake of pond when air moves across the surface. When air moves over water surface of a lake the oxygen level is greatly increased.

The surface area to volume area of a lake is very different than water droplets: as Ray mentioned, they equilibrate with atmospheric gases almost instantly.

The main reason is because the air currents makes ripples in the water and the surface increases to absorb more oxygen. Maybe the air movement does not effect small bodies (drops) of water of in the same way? But it probably does.

It does not. Temperature, pressure, and pO2 determine how much O2 the water droplet can have dissolved in it. This equilibrium is reached almost instantly in tiny droplets.

As well when you refresh the air in contact with the wet leaf you are bringing in air that has a slightly higher oxygen content

This is pure speculation. We are talking about gases here.

When water evaporates what happens to the oxygen content of the remaining water?

It will remain the same, the water will off gas O2 to remain in thermodynamic equilibrium.

 

[Ray]

I think the reason that a lake's overall oxygen content increases is because the turbulence brought about by the wind stirs the water, bringing the lower-content stuff up from below so it can become more oxygenated.

As Chris said, the low surface-to-volume ratio of a lake will slow the "re-equilibration" process, but if things stay calm, it will return to the overall average dictated by the conditions.

 

[gonewild]

The surface area to volume area of a lake is very different than water droplets: as Ray mentioned, they equilibrate with atmospheric gases almost instantly.

I guess I would consider the water pooled in a Phal crown as a tiny "deep" lake.

It does not. Temperature, pressure, and pO2 determine how much O2 the water droplet can have dissolved in it. This equilibrium is reached almost instantly in tiny droplets.

I'm not talking about tiny droplets of water but rather water pooled on leaf surfaces or in leaf axils.

This is pure speculation. We are talking about gases here.

It will remain the same, the water will off gas O2 to remain in thermodynamic equilibrium.

When air currents replenish the air in contact with the water surface the air in direct contact with the water surface would have more oxygen to exchange. Just the reverse of when a rain drop falls through the atmosphere.

 

[gonewild]

I think the reason that a lake's overall oxygen content increases is because the turbulence brought about by the wind stirs the water, bringing the lower-content stuff up from below so it can become more oxygenated.

As Chris said, the low surface-to-volume ratio of a lake will slow the "re-equilibration" process, but if things stay calm, it will return to the overall average dictated by the conditions.

The water in the crown of an orchid plant is like a tiny deep lake is it not?
How much extra oxygen needs to be added to inhibit pathogen growth?

If you have no air movement in a greenhouse there is no surface disturbance but if you have a violent wind from a fan there is a lot of surface movement.

 

[gonewild]

Along the line of air movement at night decreasing the chance of disease when foliage is wet....

As air moves across the wet leaf the water evaporates. As the water evaporates the remaining water is cooled. The cooled water will absorb more oxygen from the atmosphere. Water with more oxygen will have slower pathogen growth. Now add in the cooler water temperature and you have even less pathogen growth.