The mechanics of humidity and VPD

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Nate_in_AK

Nate_in_AK

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Theoretical:

Room humidity is 25% and the tent controller is set to 65% humidity and 76F(24.4C)

If my plant can keep the tent at 65% humidity by itself, is that still over-working the plant somehow? Is there any difference to the plant how the tent reaches 65% humidity? Is the plant is achieving target humidity via the natural evaporation process vs. me using an external humidifier near the tent intake to raise the incoming humidity something I should consider? Or am I overthinking it?
 
1989cheeseSOG

1989cheeseSOG

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same thing
beware of calcium def with RH that high during bloom
around 55% is fine
 
Nate_in_AK

Nate_in_AK

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I suppose you could do some experimentation with this to prove it one way or the other if you had the resources.

Room A: 65% humidity. Tent controller set to 65% humidity.
Room B: 40% humidity. Tent controller set to 65% humidity.

It seems logical to expect that plants in tent "B" would go through more water than tent "A" because they are having to make up for the lower humidity outside the tent. If you could keep all other factors identical, I wonder if there would be any difference in yield volume or quality between the two tents.
 
1989cheeseSOG

1989cheeseSOG

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the room at 40 will blow the room at 60 for sure, at 76degree f
at 24degree C 65% rh is too much during bloom
 
Aqua Man

Aqua Man

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Theoretical:

Room humidity is 25% and the tent controller is set to 65% humidity and 76F(24.4C)

If my plant can keep the tent at 65% humidity by itself, is that still over-working the plant somehow? Is there any difference to the plant how the tent reaches 65% humidity? Is the plant is achieving target humidity via the natural evaporation process vs. me using an external humidifier near the tent intake to raise the incoming humidity something I should consider? Or am I overthinking it?
The humidity that matters is the humidity at the leaves/plants as this is where water vapor and gas exchange happens. So a sensor should be canopy height and you should have good airflow through the plant to ensure you are eliminating microclimates. This is why pruning can be important if needed.

I think most would be a little surprised at the humidity difference inside thier canopy when compared to outside.
 
Aqua Man

Aqua Man

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I suppose you could do some experimentation with this to prove it one way or the other if you had the resources.

Room A: 65% humidity. Tent controller set to 65% humidity.
Room B: 40% humidity. Tent controller set to 65% humidity.

It seems logical to expect that plants in tent "B" would go through more water than tent "A" because they are having to make up for the lower humidity outside the tent. If you could keep all other factors identical, I wonder if there would be any difference in yield volume or quality between the two tents.
Thier is a difference albeit not huge in overall yield that on a small scale grow its make or break it. It has an impact on nutrient uptake, teanspiration rates (which greatly affect leaf cooling ability) and co2 absorption, all of which affect photosynthesis and the amounts of light the plant can convert to energy.

So overall it has an effect on , growth rates, yields and quality. The amount of difference is variable.
 
Nate_in_AK

Nate_in_AK

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I think most would be a little surprised at the humidity difference inside thier canopy when compared to outside.
Seeing this is what has me curious about the mechanics. Thinking about it more, I suspect the "A" room would have major issues keeping the humidity at 65% inside the tent. In that scenario the room hosting the tent becomes the tent itself. Tent-ception. Or something.

Just finished watching this that I saw today on Reddit:

This guy reminds me of a few of my older instructors. What he says seems to make good sense, thinking about trying his formula next grow.
 
Aqua Man

Aqua Man

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Seeing this is what has me curious about the mechanics. Thinking about it more, I suspect the "A" room would have major issues keeping the humidity at 65% inside the tent. In that scenario the room hosting the tent becomes the tent itself. Tent-ception. Or something.

Just finished watching this that I saw today on Reddit:

This guy reminds me of a few of my older instructors. What he says seems to make good sense, thinking about trying his formula next grow.
Great video and great information. But imo it doesn't go to much into the details. There is optimal for stages of growth and everyone of those factors effects every other factor. There is ideal conditions even for stages of growth not to mention the genetics that also changes these needs.

Sure there is a pretty basic KPA of 1.0 that will be sufficient and I'd even say a good place start to finish.
 
Nate_in_AK

Nate_in_AK

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Sure there is a pretty basic KPA of 1.0 that will be sufficient and I'd even say a good place start to finish.
I should have been more specific - I meant his "soil" mixture of 50% peat, 50% vermiculate with a dash of dolomitic lime and gypsum. This last grow I used MG organic because I was lazy.
 
Aqua Man

Aqua Man

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I should have been more specific - I meant his "soil" mixture of 50% peat, 50% vermiculate with a dash of dolomitic lime and gypsum. This last grow I used MG organic because I was lazy.
Yeah thats a great mix. Good drainage and gas exchange.
 
pork

pork

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@Aqua Man ive seen you mention the adding supplemental co2 affects transpiration. In order to take advantage of proper vpd, should a target be a bit lower or higher than what the vpd charts out there reference?
 
Aqua Man

Aqua Man

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@Aqua Man ive seen you mention the adding supplemental co2 affects transpiration. In order to take advantage of proper vpd, should a target be a bit lower or higher than what the vpd charts out there reference?
Ideally right on. It does reduce transpiration but a better approach is to adjust the ppm to compensate. But always go by plants.

You can reduce humidity a bit and I would say a 5% lower is about right. Then the rest adjusted by increase in food if needed.
 
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