flower at 91 degrees no sign heat stress... am I crazy

[OG Tree Grower]

Rh 54% air temp 76 hottest leaf was 71 coolest was 68
Subject outdoor apple tree

Rh 57% air temp 81 max leaf temp 72 min 70
Subject- indoor marijuana plant

 

[MileHighGlass]

My humidity right now is 30% I wonder if that is playing some role into this? You got me reading about transpiration and high leaf temps. Seems there is a correlation from lack of moisture which could equate to the low humidity.

Regardless, good info to be gained by the dialogue.

 

[MileHighGlass]

Read this

2. Radiant temperature

Radiant temperature is the result of heat transfer bewteen objects at different temperatures without whats inbetween i.e. the air, being effected. In our case the plants are naturally at a lower temperature that the light and reflector so heat is transferred to the plants foliage from the light/refecltor through radiation. This causes the leaves to heat up. The plants can withstand much higher radiant temperatures (around 40-50degC) than they can air temperatures but if this is too high the plants can 'burn'.

The plants can withstand much higher radiant temperatures than they can air temperatures, but if this is too high the plants can “burn”.

'The hand test': Place your hand in a comfortable position for some time at the tips of your plants should be. If your hand feels “hot”, then the lights are too close, the radiant energy is too intense, and light burn may result. Do this test and raise your HID lights/reflectors periodically to keep light burn to a minimum.

Finally, monitor the conditions in your grow regularly as things are changing all the time, and you will soon get to understand the thermal dynamics of your particular grow space so you can get the most from it.

 

[OG Tree Grower]

I can't debate much else today. Busy getting the boat ready but I will say this.

I have never got a leaf temp higher than air temp.ever
I have never got a leaf temp over 85f even in a room that's 100f with a broken air handler.

That's all experince that applies directly to marijuana. I'm no botanist so I can't speak for other plants.

 

[Snook]

I can't debate much else today. Busy getting the boat ready but I will say this.

I have never got a leaf temp higher than air temp.ever
I have never got a leaf temp over 85f even in a room that's 100f with a broken air handler.

That's all experince that applies directly to marijuana. I'm no botanist so I can't speak for other plants.

hard to believe OG.. how big was that fish??

 

[OG Tree Grower]

Do I detect Sarcasm snook?

Not very big man. Watched 3 boats catch fish and got skunked. Not good at all for the first day out

 

[Snook]

Do I detect Sarcasm snook?

Not very big man. Watched 3 boats catch fish and got skunked. Not good at all for the first day out

Me? Sarcastic!? Surely you jest.
But really.. never? Indoors.

 

[OG Tree Grower]

Lol sometimes I can't pick up on it.

No seriously never. Have you?

 

[Snook]

Lol sometimes I can't pick up on it.

No seriously never. Have you?

I don't pay that much attention to it actually. maybe I should, I have an infrared thermometer and it isn't hard to use.
my first thought is without a doubt in the past at some leaf temp had to have been higher than ambient but the more I type and think about it, the leaf would almost have to be dead for that to happen.. I dono..


EDIT: afterall OG, 'never' is a long time to remember.

 

[OG Tree Grower]

I used to be hardcore when I lived at these ops, spent at least 6-8 hours a day in a little 10 lighter before I was allowed to take care of anything substantial . lota of little experiments, cleaning and learning about plants.

Yes the plant or leaf would have to be dead to be warmer than the air.

 

[Snook]

I used to be hardcore when I lived at these ops, spent at least 6-8 hours a day in a little 10 lighter before I was allowed to take care of anything substantial . lota of little experiments, cleaning and learning about plants.

Yes the plant or leaf would have to be dead to be warmer than the air.

I used to spend that much time in the basement on the pool table practicing.. I was pretty good... now I cant see 2well
EDIT:should have said see well enough to play pool

 

[stoned-trout]

cooler grown weed in my gardens, leads to better smells and better density buds than warmer temps...I have grown in some hot ass places inside an out .....yeehaw..real cool temps give me the best colors like in winter here in so cal...

 

[stoned-trout]

I played pool almost every day for about 20 years once even in florida...pool halls were my home lol and tourist dollars in my pocket in Daytona..cant play much now as my wrist been broken 2x and is screwed and my sight is slowly going...if it weren't for the pain I would try tho...yeehaw

 

[dr-dank]

good thread.

I did some goog.

Does seem that science confirms in almost all cases leaf temp should be lower than air. In fact, some use the difference (or lack of) to predict water stress and therefore when to irrigate.

I wonder if the OP who has measured leaf temp higher is not in fact confirming water stress? IOW, perhaps raising humidity would bring leaf temp down and in fact improve things?

"because a difference between the temperature of air and that of canopy (temperature difference) is a generally accepted indicator of water availability to plants (e.g.
JACKSONet al. 1977, 1981; KEENER & KIRCHER1983; PAW U1984, and OLUFAYOet al. 1994). In the period of water stress temperature difference is influenced not only by the increasing surface resistance to water vapour"

http://www.agriculturejournals.cz/publicFiles/82030.pdf

http://www-das.uwyo.edu/~geerts/cwx/notes/chap03/leaves.html

"Foliage exposed to the Sun is rarely at a temperature equal to that of the air around, because evaporation cools the leaves and sunshine heats them. The drier the air, the cooler the leaf of a well-watered plant is, compared to the surrounding air. A comparison of reported temperatures of the leaves of numerous well-watered plants in various parts of the world around midday, and of the adjacent air (T), indicated that the temperature difference between the leaf (T) the ambient air (Ts), (T - Ts), decreases as T rises (1). The difference tends to be positive at low air temperatures but negative in hot conditions. In the Australian study (1), it is about zero at around 30�C. This was subsequently corroborated in a survey of measurements by other people (2)."

 

[Huckster79]

This vpd thing is fascinating and Iv been following it to a tee on accident! Lol. Was Warmer and more humid than "ur supposed to be" and been rocking it out for no more experience than I have- makes more sense now... I wasn't too humid just the old boiler plate "knowledge" we are all given just is t accurate for every situation in finding out at every turn

 

[Dropped Cat]

I grow in a small cabinet, non climate controlled and
I used to skip summer months flowering, until I read
that more plants in the space allow for better flowers
in high heat.

Ambient temps are 90F for days on end, plants are
not at their best, but I get harvests.

If I could get RH higher my plants would suffer less.

Maybe line the wall with sponges and spray it down.

lol

 

[Huckster79]

Mine naturally stays around 70rh. Then last run last two weeks I throw a bag of silica cat litter in my stink eater n it'll drop down to mid 50s... My stink eater is a homade rig like most my shit- 5 gall bucket w a fart fan fitted on top n holes drilled in bottom 1/3 of bucket- fill her w lump charcoal n sit a homade activated charcoal filled screen on top of the lump charcoal. I figured out a way to get about 6" more height out of my light- dropped canopy temp back to my mid 80s where I know they'll b happy. Not showing any signs of stress from their 90+ week, and they smell amazing I know some say that's first to go in high heat... I brushed up against one other night just checking temp not working in room just quick Check came back upstairs n gf said I reeked... . I think that "too high humidity" along w the co2 saved em from any real harm

 

[OG Tree Grower]

Thanks for the science backup dr dank!

 

[MileHighGlass]

good thread.

I did some goog.

Does seem that science confirms in almost all cases leaf temp should be lower than air. In fact, some use the difference (or lack of) to predict water stress and therefore when to irrigate.

I wonder if the OP who has measured leaf temp higher is not in fact confirming water stress? IOW, perhaps raising humidity would bring leaf temp down and in fact improve things?

"because a difference between the temperature of air and that of canopy (temperature difference) is a generally accepted indicator of water availability to plants (e.g.
JACKSONet al. 1977, 1981; KEENER & KIRCHER1983; PAW U1984, and OLUFAYOet al. 1994). In the period of water stress temperature difference is influenced not only by the increasing surface resistance to water vapour"

http://www.agriculturejournals.cz/publicFiles/82030.pdf

http://www-das.uwyo.edu/~geerts/cwx/notes/chap03/leaves.html

"Foliage exposed to the Sun is rarely at a temperature equal to that of the air around, because evaporation cools the leaves and sunshine heats them. The drier the air, the cooler the leaf of a well-watered plant is, compared to the surrounding air. A comparison of reported temperatures of the leaves of numerous well-watered plants in various parts of the world around midday, and of the adjacent air (T), indicated that the temperature difference between the leaf (T) the ambient air (Ts), (T - Ts), decreases as T rises (1). The difference tends to be positive at low air temperatures but negative in hot conditions. In the Australian study (1), it is about zero at around 30�C. This was subsequently corroborated in a survey of measurements by other people (2)."

Check this link about radiant heat absorption of leaves.
http://www.jstor.org/stable/1935253?seq=1#page_scan_tab_contents

As I always say show me a study, and I will show you the opposite study.

Every leaf I take a temperature of in direct sunlight is hotter than air temperature.

We all have so much to learn from plants, and each other. This is an interesting subject though.

 

[Elmer Bud]

good thread.

I did some goog.

Does seem that science confirms in almost all cases leaf temp should be lower than air. In fact, some use the difference (or lack of) to predict water stress and therefore when to irrigate.

I wonder if the OP who has measured leaf temp higher is not in fact confirming water stress? IOW, perhaps raising humidity would bring leaf temp down and in fact improve things?

"because a difference between the temperature of air and that of canopy (temperature difference) is a generally accepted indicator of water availability to plants (e.g.
JACKSONet al. 1977, 1981; KEENER & KIRCHER1983; PAW U1984, and OLUFAYOet al. 1994). In the period of water stress temperature difference is influenced not only by the increasing surface resistance to water vapour"

http://www.agriculturejournals.cz/publicFiles/82030.pdf

http://www-das.uwyo.edu/~geerts/cwx/notes/chap03/leaves.html

"Foliage exposed to the Sun is rarely at a temperature equal to that of the air around, because evaporation cools the leaves and sunshine heats them. The drier the air, the cooler the leaf of a well-watered plant is, compared to the surrounding air. A comparison of reported temperatures of the leaves of numerous well-watered plants in various parts of the world around midday, and of the adjacent air (T), indicated that the temperature difference between the leaf (T) the ambient air (Ts), (T - Ts), decreases as T rises (1). The difference tends to be positive at low air temperatures but negative in hot conditions. In the Australian study (1), it is about zero at around 30�C. This was subsequently corroborated in a survey of measurements by other people (2)."

G`day Dr D

Ultra low humidity the stomata close and the plant doesn`t move water and nutes through .
No cooling via water vapor . Sealed up leaf under the heat of the lamps = ?

Ultra high humidity the plants can`t produce vapor as efficiently water in the air is pushing back at the stomata .

Thanks for sharin

EB .