Leaf temperature.

Can someone explain why the leaf temperature of my plants are 5⁰ F lower than my 80⁰ F tent temperature?

I've tried searching for an answer but nothing explaines it.

It’s usually because the leaves are evaporating moisture.

Budzbuddha said:

It’s usually because the leaves are evaporating moisture.

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Thanks, It confusing that it at a lower temperature than the air temperature.

I could see a couple of degrees, But not 5 degrees.

yea, its cooler from water evaporating. Water changing from fluid to vapor and vice versa can release or absorb alot of heat. Example of the opposite is for frost protection fruit trees will get sprayed with water, its the water constantly freezing that is giving off heat.

Blue_Focus said:

Thanks, It confusing that it at a lower temperature than the air temperature.

I could see a couple of degrees, But not 5 degrees.

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That's unusually high but it's indicative of lots of air flow and lowish humidity…or a busted thermometer.

Per @Budzbuddha, as the plants transpire, they give off water vapor and the evaporating water lowers the temperature of the leaf surface and a tiny layer of air above the leaf surface. The temperature drop is a function of "the latent heat of evaporation" (Google) and that's a mechanism that plants and animals use to cool off. In most cases, the LST offset will be -2°F but when the offset is higher, it indicates that the environment is more conducive to evaporation. Wind speed and RH are drivers of evaporation.

Delps8 said:

That's unusually high but it's indicative of lots of air flow and lowish humidity…or a busted thermometer.

Per @Budzbuddha, as the plants transpire, they give off water vapor and the evaporating water lowers the temperature of the leaf surface and a tiny layer of air above the leaf surface. The temperature drop is a function of "the latent heat of evaporation" (Google) and that's a mechanism that plants and animals use to cool off. In most cases, the LST offset will be -2°F but when the offset is higher, it indicates that the environment is more conducive to evaporation. Wind speed and RH are drivers of evaporation.

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They are definitely putting out the humidity. My AC Infinity 4" fan is constantly kicking on.

I also have plenty of inside air flow blowing everywhere.

My house humidity stays around 40% year around.

I'm at 65% humidity and a temperature of 78⁰ F currently in my tent.

Blue_Focus said:

They are definitely putting out the humidity. My AC Infinity 4" fan is constantly kicking on.

I also have plenty of inside air flow blowing everywhere.

My house humidity stays around 40% year around.

I'm at 65% humidity and a temperature of 78⁰ F currently in my tent.

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Nice to have a steady RH!

At 78 and 65, the grow is a little cool/moist unless you're in seedling. I go with 1.0 in veg and then >=1.2 in flower.

And I just checked my tent and LST offset is -3 vs -5 a few days ago (day 60 of flower).

The DIY Koolatron drier thread here on RIU turned me on to the "Pohl Schmitt Electric Dehumidifier". It's a little $40 dehu and I've been running it in my tent for the last few weeks. My current plant is relatively "modest" in size (I f'd it up by putting too much H2O2 in the humidifier res) but that little dehu looks to be good for about a 7% drop in RH. I lost a beautiful plant to bud rot a year ago so I'm erring on the side of caution. Just a thought…

Delps8 said:

Nice to have a steady RH!

At 78 and 65, the grow is a little cool/moist unless you're in seedling. I go with 1.0 in veg and then >=1.2 in flower.

And I just checked my tent and LST offset is -3 vs -5 a few days ago (day 60 of flower).

The DIY Koolatron drier thread here on RIU turned me on to the "Pohl Schmitt Electric Dehumidifier". It's a little $40 dehu and I've been running it in my tent for the last few weeks. My current plant is relatively "modest" in size (I f'd it up by putting too much H2O2 in the humidifier res) but that little dehu looks to be good for about a 7% drop in RH. I lost a beautiful plant to bud rot a year ago so I'm erring on the side of caution. Just a thought…

View attachment 5386547

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I find that they grow faster and have gotten bigger at 65% vs 55% I did on my last grow.

I'll lower the humidity when they start flowering.

Blue_Focus said:

I find that they grow faster and have gotten bigger at 65% vs 55% I did on my last grow.

I'll lower the humidity when they start flowering.

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Interesting — VPD-wise, that RH is a little high but we're not harvesting VPD!

Delps8 said:

Nice to have a steady RH!

At 78 and 65, the grow is a little cool/moist unless you're in seedling. I go with 1.0 in veg and then >=1.2 in flower.

And I just checked my tent and LST offset is -3 vs -5 a few days ago (day 60 of flower).

The DIY Koolatron drier thread here on RIU turned me on to the "Pohl Schmitt Electric Dehumidifier". It's a little $40 dehu and I've been running it in my tent for the last few weeks. My current plant is relatively "modest" in size (I f'd it up by putting too much H2O2 in the humidifier res) but that little dehu looks to be good for about a 7% drop in RH. I lost a beautiful plant to bud rot a year ago so I'm erring on the side of caution. Just a thought…

View attachment 5386547

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Nice I keep my tent around 1.3-1.5 in flowering and my plant seems happy.

UnknownRemedy said:

Nice I keep my tent around 1.3-1.5 in flowering and my plant seems happy.

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[Edit for clarification] - the above text is perfectly valid. I inadvertently included in my original reply.

Delps8 said:

Nice to have a steady RH!

At 78 and 65, the grow is a little cool/moist unless you're in seedling. I go with 1.0 in veg and then >=1.2 in flower.

And I just checked my tent and LST offset is -3 vs -5 a few days ago (day 60 of flower).

The DIY Koolatron drier thread here on RIU turned me on to the "Pohl Schmitt Electric Dehumidifier". It's a little $40 dehu and I've been running it in my tent for the last few weeks. My current plant is relatively "modest" in size (I f'd it up by putting too much H2O2 in the humidifier res) but that little dehu looks to be good for about a 7% drop in RH. I lost a beautiful plant to bud rot a year ago so I'm erring on the side of caution. Just a thought…

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That should read 1.2 to 1.5 in flower.

Delps8 said:

That should read 1.2 to 1.5 in flower.

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Probably. But my phone auto corrects and generally I just don't really care to correct my English after I already posted.

UnknownRemedy said:

Probably. But my phone auto corrects and generally I just don't really care to correct my English after I already posted.

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Your posting is completely valid. My reply mistakenly included yours.

I was replying to my posting which read ">1.2" and that's not quite correct. I should have posted "1.2 - 1.5".

My apologies for the confusion.

Delps8 said:

Your posting is completely valid. My reply mistakenly included yours.

I was replying to my posting which read ">1.2" and that's not quite correct. I should have posted "1.2 - 1.5".

My apologies for the confusion.

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Ohh yeah haha no worries. My house runs dry so It drops down to 1.6 before the humidifier kicks in and I haven't seen a problem. So as long as it's not sitting above it for too long you should be fine.

Bullmark said:

I sometimes get as much as a 5 degree difference…..and sometimes it’s only 1 or 2 degrees. It’s hard to get a consistent RH evenly distributed in a specific space. When it’s 60% at my canopy, it can easily be 70-72% at the base of the plant….which is about 2 ft lower.
I used to obsess over it but not anymore.

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Yeah, humidity drops rather than rising. Having a fan lower near the base keeps the air moving.

Bullmark said:

I sometimes get as much as a 5 degree difference…..and sometimes it’s only 1 or 2 degrees. It’s hard to get a consistent RH evenly distributed in a specific space. When it’s 60% at my canopy, it can easily be 70-72% at the base of the plant….which is about 2 ft lower.
I used to obsess over it but not anymore.

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You need more sir movement no doubt and a small space should stay equal throughout easily

Delps8 said:

Interesting — VPD-wise, that RH is a little high but we're not harvesting VPD!

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Think of it this way at ambient atmospheric co2 plants can use about 400 ppm regularly.. to up co2 u need more light more food more water .. MORE TEMPERATURE AND HUMIDITY ARE also hand in hand sliding scale in veg.. transportation rates are upped with the metabolic rate and unless in flower it's perfectly fine to get up to 78 and 65+ humidity.. don't try that in flower before harvest tho

Fano_man said:

Think of it this way at ambient atmospheric co2 plants can use about 400 ppm regularly.. to up co2 u need more light more food more water ..

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Re. which input to increase - you might want to view the videos by Dr. Bruce Bugbee. He states that CO2 is the first input that should be increased because it's the cheapest.

Supporting this is the fact that we have observed that the area covered by forests is increasing as CO2 levels have increased. This is not the "correlation ≠ causation" fallacy because it's occurring around the globe and the other inputs are not changing.