Foliage watering

Hi community, I heard in a video from Ryan that is not good watering the foliage because it impacts the vegetative growth. I always supposed that foliage watering could encourage fungus but never have heard about impacts in the growth. Could some of the experts share some biological explanation?

Thanks in advanced,

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Hi @wilson_chiesa

As far as I understand it’s due to the film of water temporarily “sealing” over the stomatal pores of the leaves, stopping gas exchange (including co2) and so halting photosynthesis until the water has evaporated.

I imagine it’s one of those things that every now and then won’t make a lot of difference, but could mount up if there’s a routine pause in the tree’s ability to photosynthesis after you water each day.

Probably something that’s more applicable to bear in mind if you defoliate/partial-defoliate once or twice each growing season.


I can say definitively from my specific experience with Chinese elm saplings that they not only enjoy misting the foliage, but seem to basically require it. I used to mist the foliage a few times a day on my entire small collection of trees, until I heard Ryan say that he general avoids watering foliage. That was a few months ago.

My three elm saplings stagnated at that point. A couple weeks ago, I though, “jeez, these guys have seen better days, maybe I should start misting again.” And, sure enough, they perked back up, with all three pushing new growth in a matter of days.

Apart from that very limited experiment, I can say that my ficus seems to very much appreciate foliage misting, as well. I imagine this is the case for all tropical plants. I can’t speak to the exact biological mechanisms involved, but dense, moist, misty air is their native environment.


I seem to recall the discussion being about hot days when the trees are transpiring (losing water) to cool themselves. Watering the foliage will increase the relative humidity around the leaves and reduce transpiration and therefore reduce cooling until it all evaporates.

There is also the issue of keeping the foliage too moist during cooler weather and/or overnight which can provide a good environment for fungal growth.


The process of evaporation cools. It’s why humans sweat. If misting plants on a hot day slows transpiration (I’m not sure it does), that shouldn’t reduce cooling (since, again, the water being sprayed on the leaves is evaporating and, thus, cooling).

Michael Hagedorn’s new book, “Bonsai Heresy,” has a section on some of the myths surrounding watering foliage (including the idea that water droplets focus the sun like a magnifying glass and create burn spots on leaves - Hungarian scientists actually performed an experiment disproving this idea). Pretty interesting stuff.

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I’m trying to process the cooling concepts in this thread.
Would the gas exchange mentioned by @Ralph cool the complete plant from the interior while misting would produce more of a surface effect? What about relative humidity?

I realize that I’m not in your league heat-wise, but are you all speaking from the same climate zone? At 9pm I’m enjoying 57F and 82% humidity after experiencing a high of 63F today. The forecast indicates 3 days in the mid-70’s this week - a heat wave!
The new neighbour has just added a 6’ high black aluminum fence across the east-facing property line. I’m trying to figure out how to make use of the heat captured. Please let me know if you have experience or suggestions.

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I think it’s been asked and answered in the Live Q&A’s somewhere. The tendency could be to draw a misguided parallel between the evaporation-cooling effect of sweating as humans, to trees transpiring to cool down.

When someone sees leaves suffering (wilting or drying) they may think the tree is hot and proceed to water the foliage. They see an improvement and might think we’ve cooled the tree down through evaporation-cooling.

But what’s actually happening is the same as my earlier post (but in this case can be done intentionally and to our advantage). Water sealing the stomata stops the absorption of atmospheric co2 and so halting photosynthesis as well as stopping transpiration. The result is a pause for the tree allowing time for the roots to catch up in supplying water to the leaves.

As far as I’m aware, higher RH reduces transpiration rate while the tree still absorbs co2 and photosynthesises. Whether the reduced transpiration has an effect on the rate of photosynthesis, I’d like to know.

I’m under the impression it’s the roots which more susceptible to heat than anything else.

@cab_lad_70 with your neighbour’s fence I can think of utilising the heat from the fence in late winter sun to warm the soil and increase activity in the roots. I’d be cautious of it in the summer sun though.


Thanks community for sharing such valuable information. In my case, I live in Chile in Santiago state, where never rains practically during 8 months (extremely dry climate), and with temperatures above 38 degrees celcius (in summer). When watering, including the foliage, it evaporates completely in less than 30 minutes. I suppose in this case the transpiration process shouldn’t be affected. It sounds correct? Best regards, Wilson.

I live in los Angeles and in my opinion its very crucial to mist. it gets very hot and the air is dry in the summer. It was 110 in my area yesterday, i think it was a record breaker, i did prepare and made sure the my trees where protected from the heat wave.

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