Follow VPD chart during flower?

[CF89]

I used the chart for veg and seemed to work good. But during flower I want the humidity lower. Granted it’s a tad low right now for being 3 weeks into flower... but I still don’t want to follow this chart during flower do I? As I’m going to want the humidity around 40-50% max during late stages of flower right?

 

[Growrx]

In for info

 

[ThisGuy420]

Bump, because I want to know too.
I struggle to maintain 65%-70% at 72-75°F

 

[growsince79]

Imo as long as you have good airflow 60%rh isn't too high. Keep the exhaust going all night or it could get way higher during dark. I shoot for 50% the lights on. 40-60 is ok. I have an outdoor plant that did great at 108f and 18%rh. It never saw the chart.

 

[MIMedGrower]

i follow the old advice of 75-77 farenheight max and 45-60% humidity and have never had a problem related to humidity.

It has long been proven that humidity is something the plant adjusts too and does not affect growth or yield.

Vpd is being mis marketed in my opinion. It is merely a guideline for greenhouses to manage humidity to the ambient temp. A band aid so to speak. There is no science that proves a specific atmospheric pressure for all leaf transpiration. Thats actually silly with plants thriving all over the world.

Indoors we have control so we do not need to compromise.


I am aware this opinion will start an argument. ;-)

 

[redshift75]

so there is no way in the life of me one can say this tent followed any sort of rule of thumb other than being a responsible grower and knowing how to maintain those conditions. my stuff is always too high. Thats why i give daily mold treatments as a foliar. "a foliar when its too wet?" yeah. You can maintain anything if you understand your environment and their reactions. I look at these and im not mad at them at all... Pictures are out of time line. Im dropping these things down to like 30 degrees with high humidity to create frost. I mean. Its all about confidence. If i went into this like "what do i do" it will fail. I go into it everyday saying how can i deal with todays conditions. no issues. growing big growing good. All my tents are doing amazing. My main tents outside of temps are good for RH but even then to the whole scale. I compare my mid summer harvest to this. its looking right now about identical.

***note white spots are my folairs and washes off not WPM.

 

[growsince79]

i follow the old advice of 75-77 farenheight max and 45-60% humidity and have never had a problem related to humidity.

It has long been proven that humidity is something the plant adjusts too and does not affect growth or yield.

Vpd is being mis marketed in my opinion. It is merely a guideline for greenhouses to manage humidity to the ambient temp. A band aid so to speak. There is no science that proves a specific atmospheric pressure for all leaf transpiration. Thats actually silly with plants thriving all over the world.

Indoors we have control so we do not need to compromise.


I am aware this opinion will start an argument. ;-)

I only ever had mold once. The room RH was under 50%. Only one freak nod that was just too big and dense to grow. It was F1 Colombian x Afghan that had been in flower almost 90 days and was as big round as a softball.and hard as a rock and still had a long way to go.

 

[Aqua Man]

As was said good airflow. And I agree with @MIMedGrower these are guidelines.

BUT!!!! To many people use it wrong and that leads to the dreaded issues you hear about.

YOU MUST TAKE LEAFS TEMPS INTO ACCOUNT.

Will leave this here.

VPD (vapor pressure deficit)

Ok i was gonna sit down and write out a whole article but i have been lazy so instead instead I'm going to copy paste because im lazy. This is not my work so let start. You may find this very long but its worth the read. Some may want to skip ahead. I have added here and there to what i feel is...

www.thcfarmer.com

 

[Aqua Man]

I only ever had mold once. The room RH was under 50%. Only one freak nod that was just too big and dense to grow. It was F1 Colombian x Afghan that had been in flower almost 90 days and was as big round as a softball.and hard as a rock and still had a long way to go.

I agree low humidity is just as bad as high humidity for causing mold issues and the worste conditions are high and low fluctuations.

 

[MIMedGrower]

I only ever had mold once. The room RH was under 50%. Only one freak nod that was just too big and dense to grow. It was F1 Colombian x Afghan that had been in flower almost 90 days and was as big round as a softball.and hard as a rock and still had a long way to go.

Me too. A huge flower just next to the window air conditioner got black mold. Only mold i have seen in my gardens other than some pm inside the clone dome.

I moved the window ac out of tje flower room and now blow air conditioned air in through intake fans from the room next door. And not directly on the plants.

And i have stopped using the dome and clones rooted fine in the open air.

 

[redshift75]

I agree low humidity is just as bad as high humidity for causing mold issues and the worste conditions are high and low fluctuations.

These have only been grown in high low Most days its 90% then drops to like 40%. But you know thats why im spraying them daily. So left to its own devices worst thing. I did have mold issues before i defoliated. I had left it au natural and that was the issue. Cause i had no air flow in the canopy. that was when i started flower it popped its head. Good 50% trim back and has been fine with the sprays. :fingers crossed:

 

[MIMedGrower]

I agree low humidity is just as bad as high humidity for causing mold issues and the worste conditions are high and low fluctuations.

Temp fluctuations while humid would be the biggest danger. Going cooler while room is too wet.

 

[MIMedGrower]

As was said good airflow. And I agree with @MIMedGrower these are guidelines.

BUT!!!! To many people use it wrong and that leads to the dreaded issues you hear about.

YOU MUST TAKE LEAFS TEMPS INTO ACCOUNT.

Will leave this here.

VPD (vapor pressure deficit)

Ok i was gonna sit down and write out a whole article but i have been lazy so instead instead I'm going to copy paste because im lazy. This is not my work so let start. You may find this very long but its worth the read. Some may want to skip ahead. I have added here and there to what i feel is...

www.thcfarmer.com

I know you are a huge fan of this technique but it still doesnt make any sense. Who decided what conditions are optimal for the specific plant?

Just like high and low light plants. Tropical and mountain plants. Or any different plant they all have different light requirements, nutrient requirements and environmental preferences. Our plant has evolved to grow most anywhere.


And if it was really important i think the university of utah cannabis lab would be recommending it. They do not. They recommend keeping humidity indoors around 50%.

 

[Aqua Man]

Temp fluctuations while humid would be the biggest danger. Going cooler while room is too wet.

Yes. That because RH is relative to temps. As the temos drop the humidity spikes. I would say #1 cause is light go out and humidity spikes and boom we have ideal conditions for germination of mold and fungus. Lights go back on RH drops and ppl keep it to low and boom we have ideal conditions for spores... rinse and repeat we have a massive infection in no time.

 

[Aqua Man]

I know you are a huge fan of this technique but it still doesnt make any sense. Who decided what conditions are optimal for the specific plant?

Just like high and low light plants. Tropical and mountain plants. Or any different plant they all have different light requirements, nutrient requirements and environmental preferences. Our plant has evolved to grow most anywhere.


And if it was really important i think the university of utah cannabis lab would be recommending it. They do not. They recommend keeping humidity indoors around 50%.

Most horticulturist agree a KPA of 1.0 is a good place for majority of plants not from extreme regions. Cannabis falls in there. Sure 50% is fine and nothing wrong with it. We are just talking about fine tuning here. Also VPD IMO is most impact full in medias that provide the fastest growth such as hydro or aeroponics. But its still good practice even if its not a must.

 

[Aqua Man]

I know you are a huge fan of this technique but it still doesnt make any sense. Who decided what conditions are optimal for the specific plant?

Just like high and low light plants. Tropical and mountain plants. Or any different plant they all have different light requirements, nutrient requirements and environmental preferences. Our plant has evolved to grow most anywhere.


And if it was really important i think the university of utah cannabis lab would be recommending it. They do not. They recommend keeping humidity indoors around 50%.

But you see with a humidity of 50% that is a recommendation that involves VPD even if not used by name. In our temps that many of us use this is acceptable range but that doesn't make it the ideal range necessarily for all stages if growth. Much like VPD is a guideline because some plants like the lower end of the recommendation and some like the higher end. Its not a one size fits all but much like a more detailed guidelines of say your 50% recommendation is all.

 

[MIMedGrower]

Most horticulturist agree a KPA of 1.0 is a good place for majority of plants not from extreme regions. Cannabis falls in there. Sure 50% is fine and nothing wrong with it. We are just talking about fine tuning here. Also VPD IMO is most impact full in medias that provide the fastest growth such as hydro or aeroponics. But its still good practice even if its not a must.

Do you have a link to a test proving your assertion? Because most growers are more worried about too high humidity. And even back in ed rosenthals book and others he tested a wide range of humidity and saw no difference in yield or quality.

 

[Aqua Man]

Do you have a link to a test proving your assertion? Because most growers are more worried about too high humidity. And even back in ed rosenthals book and others he tested a wide range of humidity and saw no difference in yield or quality.

Sure ill dig some up when I get home. Lots out there.

 

[MIMedGrower]

But you see with a humidity of 50% that is a recommendation that involves VPD even if not used by name. In our temps that many of us use this is acceptable range but that doesn't make it the ideal range necessarily for all stages if growth. Much like VPD is a guideline because some plants like the lower end of the recommendation and some like the higher end. Its not a one size fits all but much like a more detailed guidelines of say your 50% recommendation is all.

My rec is to keep it above 45 and below 60 so it is in a safe stable range. Just like temps need to be kept tight.

Plants like stability.

 

[MIMedGrower]

Sure ill dig some up when I get home. Lots out there.

Thank you.