"Overcoming mid-day senescence" via irrigation-timing? (IE *dramatically* increased growth rates)

SU2

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Wanted to bring this up, both to find what others can tell me and to share it if anyone's not making-use of something they could be... This of course only applies to growth during the times where the midday heat & UV is so intense that broadleafs are wilting (a protection mechanism IIRC) since they cannot transpire enough to adequately function. This is the norm here for me, it's "spring" but today hits 85deg and few clouds overhead.

It's really struck me in the past year when seeing progression albums, and seeing the growth of my own stuff (not going to do a pictures/numbers contest lol), but have seen other FL growers' pictures of 2 and 3 years' growth on a leader-primary that they're trying to close a full trunk-chop wound with, and they'll have what I can get in half a year! I know part of that is a walter pall style mindset for feeding & flushing substrate (and hosing crowns!!), and part is using rainwater & correcting pH when using tap-water (both via acidic fortification, and choosing more acidic substrates & top-dressings), but I now know for sure a very large portion of my growth is coming from the midday irrations my trees typically get..

If I come home at 3p and nobody watered my trees for me, they are wilted so hard...have heard the term "midday senescence" for this before...at any rate I don't have hard-#'s but "eliminating" this senescence by hosing-down the trees a couple times during the height of the afternoon seems to have as big an effect on growth as any other important aspect does, all I can reason is that their wilted midday 'senescence' when the sun is too-much is a period they're "retreating" instead of "growing" and that you're effectively eliminating that -- this isn't just more hours/day of growth, it's allowing the hours with the highest UV rates to be hours the plant can stand strong, leaves turgid, sucking-in all that sweet UV ;D

Think that's enough on it, am very curious what others have found in this area, or think about it! Again I'm guessing this phenomena isn't nearly as strong in, say, GA or MA.
 

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Midday watering may well solve your problem but it could also bring up another whole new set of problems. Try looking at other aspects as well as just frequency of water.
I'm wondering if other factors could also be modified.
Just for context my area has hot (regular 100F+ days) and dry with typical very low humidity through summer. I don't use midday watering but have learned to modify other factors to mitigate daily wilting. I still find that a few trees in smaller pots are just starting to wilt by the end of the day but consider that is probably a good thing as they are typically the ones I want less growth from and it indicates I am not over watering.

Pot size has a big impact on the amount of water available and the amount of subsequent growth. If I want plenty of growth the trees are in larger pots. When comparing growth of other growers you also need to compare pot size and other cultural practices, not just water alone. I have also found that my advanced trees do far better in slightly deeper pots than was typically used in the past so I have stopped using excessively shallow pots.

Water effectively: It took many years to recognize that watering needs to be effective rather than frequent. Autopsies showed that water was not always getting through to the centre of the pots which obviously leaves the trees short of water each day. It is a little hard to explain and there are many mitigating factors that influence how to water effectively but well worth considering.

Soil type: Most are aware that the type of soil used can make a big difference to how much water and nutrient is retained in a pot. Just because someone else in another area uses a special mix and the trees do well does not mean that mix is ideal for you or me. Many of my customers find the soil I use does not suit their requirements and need to change to something that works better for their area and care regime. Consider modifying the soil mix you use.

Trees that regularly show severe wilting are placed on humidity trays so they have access to humidity and extra water through the heat of the day. This works really well for shohin bonsai and others in relatively small pots.

Good luck with overcoming these difficulties.
 

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I agree that making sure that plants are turgid through the heat of day makes for more growth. I use a high organic mix with no rocks and deeper than typical pots to make sure that the plants do not ever get to the wilting stage, which I think sets-back a plant. The theory I abide is the plants are using all the water of transpiration to transport the building blocks of food production and there is no such thing as wasted effort, there is only 100% utilization. It's why they can irrigate deserts and produce abundant crops.
 

SU2

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tl;dr-- I'm not trying to overcome anything, but trying to share & understand this phenomena I'm seeing in my garden-- it's as-if the midday irrigations, timed to negate midday wilting/senescence, have had as-big an effect on growth-rate as, say, rectifying a nitro deficiency, or upgrading sun-intake by 25%!


Midday watering may well solve your problem but it could also bring up another whole new set of problems. Try looking at other aspects as well as just frequency of water.
I'm wondering if other factors could also be modified.
Just for context my area has hot (regular 100F+ days) and dry with typical very low humidity through summer. I don't use midday watering but have learned to modify other factors to mitigate daily wilting. I still find that a few trees in smaller pots are just starting to wilt by the end of the day but consider that is probably a good thing as they are typically the ones I want less growth from and it indicates I am not over watering.

Pot size has a big impact on the amount of water available and the amount of subsequent growth. If I want plenty of growth the trees are in larger pots. When comparing growth of other growers you also need to compare pot size and other cultural practices, not just water alone. I have also found that my advanced trees do far better in slightly deeper pots than was typically used in the past so I have stopped using excessively shallow pots.

Water effectively: It took many years to recognize that watering needs to be effective rather than frequent. Autopsies showed that water was not always getting through to the centre of the pots which obviously leaves the trees short of water each day. It is a little hard to explain and there are many mitigating factors that influence how to water effectively but well worth considering.

Soil type: Most are aware that the type of soil used can make a big difference to how much water and nutrient is retained in a pot. Just because someone else in another area uses a special mix and the trees do well does not mean that mix is ideal for you or me. Many of my customers find the soil I use does not suit their requirements and need to change to something that works better for their area and care regime. Consider modifying the soil mix you use.

Trees that regularly show severe wilting are placed on humidity trays so they have access to humidity and extra water through the heat of the day. This works really well for shohin bonsai and others in relatively small pots.

Good luck with overcoming these difficulties.
Am not trying to overcome difficulties, rather am trying to both understand & share this phenomena I am seeing! My trees grow so fast I occasionally restrict their nutes just because I cannot keep-up with them!! No, this thread's purpose is to see if others have found this "midday irrigation = major bump in growth-rate" phenomena, I wish I'd known it when I started I could've saved a year+ on the initial development of some of my larger yamma's...

Pot size is (as you say) very important but I'd argue that pot type is just as big a consideration, and - IMO - if you're not displaying the tree for aesthetics (where you'd want to use a proper bonsai pot), then IMO grow-bags/pond-baskets/etc are the ONLY way to go for a tree that is in any real "growth" (I fully acknowledge that a finished specimen doesn't need this, am referring to the 99% of bonsai trees that are not finished!)

Will add that overwatering isn't inherently bad. It is bad if you've got inadequate drainage and substrate for your level of watering, but I use very large particle-size mixtures, and very rapid draining containers, so I can pump water all day w/o hurting anything in fact doing so helps me flush-out salts (my approach stems from the "walter pall: feeding, watering and fertilizing in plain english" description ;) )
 

SU2

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I agree that making sure that plants are turgid through the heat of day makes for more growth. I use a high organic mix with no rocks and deeper than typical pots to make sure that the plants do not ever get to the wilting stage, which I think sets-back a plant. The theory I abide is the plants are using all the water of transpiration to transport the building blocks of food production and there is no such thing as wasted effort, there is only 100% utilization. It's why they can irrigate deserts and produce abundant crops.
Heck yeah thank you this is basically what I had in my head but couldn't word well enough :p

They'll grow based on conditions, and extreme midday UV/heat can cause them to back-off of growth, instead using that energy on transpiration as you mention.....then, the gardener(us!) intervenes and gives them a "cool-down shower" midday* once or twice, virtually negating this wilt/senescence, effectively negating that midday slump!!

But it seems more than just "you're getting an extra couple hours per day", like in terms of the growth I get....I've surmised that it's gotta be (at least in-part) due to the fact that that midday period is the most "UV-ripe" period of the day, and now they can grow in it instead of shrink-back from it!

(*I should mention that I don't believe the "midday cool-down irrigation" needs to be "full" irrigation--- by this I mean that I am aiming for full canopy/trunk/surface wettings when I do this, not to properly water the substrate. I do that 1-2x/day, once in the AM and sometimes at night. The midday's are meant to act more like a quick "cloud burst" of rain, than a soil-soaking downpour!)
 

sorce

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I think a larger pot has an equal or more benefit by it's ability to remain cooler at the core, moreso than water available.

What I read about midday watering is the largest benefit is the cooling. Getting rootzone back to optimal temp for activity. See 0soyoung posts.

I found that watering at the single most optimal time is best.


Sorce
 

Forsoothe!

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Watering foliage in areas not plagued with high humidity keeps spider counts down, like especially mites. I will keep arguing that so-called humidity trays do nothing at all unless the roots can touch the water, which may be good or bad depending upon species. When you fart in a room a person on the other side of the room can detect it PDQ. That's how fast all elements in the atmosphere disperse and equalize across the whole volume of air. A frosted glass loses the frost almost as fast a bartender can fill the glass with cold beer and put the glass on the bar, which is why they use heavy glass mugs for that ~gimmick~, the mass of the mug being 5 or 6 times that of a glass will hold the frost longer, but not much. Humidity trays inside a house are laughable, and outdoors are insignificant to the point that there are no instruments that can detect the difference between the air within an inch of the tray and ten feet away. Someone is gonna say, "Oh ya, yada yada..." Well, Show Me. If the pool of water cools the pot, that's the best you can expect. If that's good, then God bless.
 

sorce

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I reckon water filled humidity trays can also keep bugs from crawling up drain holes.

Sorce
 

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Heck yeah thank you this is basically what I had in my head but couldn't word well enough :p

They'll grow based on conditions, and extreme midday UV/heat can cause them to back-off of growth, instead using that energy on transpiration as you mention.....then, the gardener(us!) intervenes and gives them a "cool-down shower" midday* once or twice, virtually negating this wilt/senescence, effectively negating that midday slump!!

But it seems more than just "you're getting an extra couple hours per day", like in terms of the growth I get....I've surmised that it's gotta be (at least in-part) due to the fact that that midday period is the most "UV-ripe" period of the day, and now they can grow in it instead of shrink-back from it!

(*I should mention that I don't believe the "midday cool-down irrigation" needs to be "full" irrigation--- by this I mean that I am aiming for full canopy/trunk/surface wettings when I do this, not to properly water the substrate. I do that 1-2x/day, once in the AM and sometimes at night. The midday's are meant to act more like a quick "cloud burst" of rain, than a soil-soaking downpour!)
I do this religiously but I just thought it was called watering my trees properly..... ;-)

Evaporation has an exponential curve with temperature. For my climate and soil mix, that means that I have to water:
once when it's 80F,
twice when it's 90F, and
three times when it's 100F.

The good thing about having so many curly willows around is that they're like canaries in a coal mine in terms of mid-day wilting. As soon as I see the shoots head south, I water everything again. And I agree that it maximizes growth. I just didn't know there was a fancy word for it.

Now of course, NONE of this mid-day tinkering around was possible before the pandemic lockdown had me working at home and looking out the window at my trees all day.

Thanks, COVID!
 

0soyoung

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Relative humidity is the driver of transpiration, the logarithm of rH more specifically.

On a day when there are no fronts blowing through, the local atmosphere has pretty much a fixed amount of water vapor in it. This is tagged in meteorological data as the dew point = the temperature at which dew forms or the temperature corresponding to100% rH.

Anyway, the point is that rH declines with increasing temperature, so the lowest relative humidity (and greatest transpiration 'stress') occurs in the heat of the day, typically around 3 to 4 pm. I showed this with real-word data in reporting my repotting experiment results, years ago. Here is an example. The splash of dots are rH readings, every 5 minutes, over the span of 5 days (the dew point shifted a little over time, but in a relatively small range around 55F).

zelfall_14mod_trh-jpg.65953

btw, the colored dashed lines in this plot are lines of constant chemical potential (transpiration stress).

One can sprinkle/mist (to temporarily elevate relative humidity close to the leaves) in addition to watering the roots to recover wilting foliage (SOP for summer repotting (Aug/Sep) in the northern hemisphere).
 

Forsoothe!

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I need help interpolating. What is (F,RH) and the column of -50 thru -500? Also,do you have a similar graph of winter rH which goes mostly opposite in that the lower the temps, the higher the evaporation rate/lower rH.
 

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Your trees are wilting because your soil isn't retaining enough water between waterings to sustain them.
So of course a mid day watering will help with that (assuming you also water in the morning). This is common sense.
Or you can change your substrate so that it retains a bit more water so the trees dont dry out before the next watering.

When we get really hot here like 90-95 F+, I sometimes have to give my trees a little water in the late afternoon as well.
So this isnt surprising
 

0soyoung

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I need help interpolating. What is (F,RH) and the column of -50 thru -500? Also,do you have a similar graph of winter rH which goes mostly opposite in that the lower the temps, the higher the evaporation rate/lower rH.
They are lines of (1/kT)*ln(rH), for a constant rH (relative humidity)
where k= Boltzman's constant
T = the Kelvin temperature <-- Celsius + 273 Of course, Celsius = 5*(Farenheit + 32)/9

The line of -200 corresponds to 50% rH (note that this dashed line approximately overlays the 50% rH line).
The line of -100 corresponds to 70% rH (square root of 50% is a touch more at 70.7%
The line of -400 corresponds to 25% rH (50% squared)
These are all very close to the y-axis values they (the dashed lines) intercept at 40F.
 

Mikecheck123

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Relative humidity is the driver of transpiration, the logarithm of rH more specifically.

On a day when there are no fronts blowing through, the local atmosphere has pretty much a fixed amount of water vapor in it. This is tagged in meteorological data as the dew point = the temperature at which dew forms or the temperature corresponding to100% rH.

Anyway, the point is that rH declines with increasing temperature, so the lowest relative humidity (and greatest transpiration 'stress') occurs in the heat of the day, typically around 3 to 4 pm. I showed this with real-word data in reporting my repotting experiment results, years ago. Here is an example. The splash of dots are rH readings, every 5 minutes, over the span of 5 days (the dew point shifted a little over time, but in a relatively small range around 55F).

zelfall_14mod_trh-jpg.65953

btw, the colored dashed lines in this plot are lines of constant chemical potential (transpiration stress).

One can sprinkle/mist (to temporarily elevate relative humidity close to the leaves) in addition to watering the roots to recover wilting foliage (SOP for summer repotting (Aug/Sep) in the northern hemisphere).
I'm in the midst of a real life experiment on humidity, having just moved from the SF Bay Area (where it's always comfortable) to Northern Virginia (where it's currently unbearably muggy).

Strangely, the relative humidity is basically similar, about 50%. But the dew point is drastically different, which makes all the difference in the world in terms of how muggy humans think it feels. For example, today the dew point was 71 in Virginia (yuck!) but only 48 in Redwood City.

This also has had an effect on my watering. I watered only once today, even though it got up to 95 degrees. I'd have had to water 2-3 times in the Bay Area at that temp. (Goes without saying that my trees were in the same soil mix as in SF.) My watering "canaries in the coal mine" (my willows), never even started to get wilting tips.

So, in sum, would it be more accurate to say that it's the dew point that makes the difference, rather than the relative humidity? Curious to hear your thoughts.
 

0soyoung

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Possibly the best way to answer your question is to refer you to the relative humidity charts/tables given by the engineering toolbox (note that temperatures are in Centigrade). A particular thing to note is that a specific rH at a specific temperature corresponds to one specific dew point temperature. In other words, what you are saying is a misperception.

The dew point being 71 degrees in Virginia means that there was so much water vapor in the air that it would condense were the temperature to somehow drop below 71F in the night (it probably didn't get that cool overnight). The Redwood City the air had far less water vapor dissolved in it, since its dew point was 48F. Redwood City's air at would be at an rH about 50% when its temperature was 71F(-ish).
 

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Possibly the best way to answer your question is to refer you to the relative humidity charts/tables given by the engineering toolbox (note that temperatures are in Centigrade). A particular thing to note is that a specific rH at a specific temperature corresponds to one specific dew point temperature. In other words, what you are saying is a misperception.

The dew point being 71 degrees in Virginia means that there was so much water vapor in the air that it would condense were the temperature to somehow drop below 71F in the night (it probably didn't get that cool overnight). The Redwood City the air had far less water vapor dissolved in it, since its dew point was 48F. Redwood City's air at would be at an rH about 50% when its temperature was 71F(-ish).
So, if a rH of 70% is comfortable at 70°F, it should be comfortable at 50 or 90°F, and 85% rH at 90, 70, or 50 would feel equally uncomfortable?
 

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And just going to raise two important points (1) the rate of transpiration varies greatly by species and (2) wetting leaves generally has a negative impact on the rate of photosynthesis (severity dependent on species). This is due to the mechanism by which wet leaf surfaces cause leaf stomata to close.
 

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So, if a rH of 70% is comfortable at 70°F, it should be comfortable at 50 or 90°F, and 85% rH at 90, 70, or 50 would feel equally uncomfortable?
If you are a tree ...

Humans have a heat producing metabolism (unlike trees). Evaporation of water we exude (sweat) is a primary mechanism by which body temperature is regulated. When the air is dry (low rH) it is easy for sweat to evaporate, so we are cooled by the loss of the heat of vaporization that is contributed to each water molecule that evaporated. If the air is saturated with water vapor (rH = 100%), none of this happens and we feel 'clammy' or worse, depending upon temperature. Likewise, when the relative humidity is just high, evaporation of sweat doesn't occur rapidly and body heat tends to build up (take it off!) and we feel discomfort. There are more compounding factors that go into our human sense of comfort.

I've been thinking a lot, getting frustrated, trying to compose a terse response. It has resulted in raising my blood pressure and pulse rate and burning more carbohydrates in my brain = all of which has raised my body temperature and put me into a most uncomfortable sweat. 🥵


A tree's comfort is not the same as a human's comfort.
 
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wetting leaves generally has a negative impact on the rate of photosynthesis (severity dependent on species). This is due to the mechanism by which wet leaf surfaces cause leaf stomata to close.

I would imagine that effect tapers off significantly shortly after evaporation. So @SU2's anecdotal experience might indicate a beneficial effect from wetting in high heat conditions that lasts longer than the detrimental effect on the stomata? But then again, unless I am missing something I don't think that they were comparing against any kind of control group, so it is just as likely that other factors are at play, including individual bias. Still, it is interesting!
 
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