VPD thread..

Thorhax

Thorhax

Well-Known Member
Vapor Pressure Deficit.
http://www.just4growers.com/stream/temperature-humidity-and-c02/vapor-pressure-deficit-the-hidden-force-on-your-plants.aspx

Lots of random information through different forums...but the prevailing idea is to keep your temps around 80 and humidity under 60%. Personally with my set ups I've always tried to keep low humidity and low temps, but I'm still a novice grower with only 3 wee years of grows.

But I've recently read some old information and have seen some new videos by people like Medicropper who have argued in favor of high temps82F+ and super high humidity80%+. They are stating conditions like these give them 4 pounds of dry premium bud per 1k hps.

I would love to hear what some OGs like @churchhaze @Uncle Ben @RM3 @ttystikk @Sativied @Dr. Who have to say (or any other good minds i failed to mention). I feel like this could really change the way a lot of people grow.
 
Thorhax

Thorhax

Well-Known Member
One thing i forgot to mention was the reason they want HIGH temps with the right VDP rather than normal temps with the right VPD is the increased rate of photosynthesis at higher temps. so with the higher temps comes the really high (75%+) humidity.

and i included some bud porn form my last harvest and the new set up. i was planning on keeping tamps at 78F day and night with 50% humidity in the day and 60% and night until i came across medicroppers video. now i have been looking all over about VPD and more evidence is pointing towards high humidity.

I would love to hear and info and support for either side of the argument.
 

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Thorhax

Thorhax

Well-Known Member
Alienwidow said:
Thats a crock.
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ok you might be right... but your not talking about VPD. lets assume your have enough air flow to support the humidity. give me some actual talk on why you think that would b good or bad? with some science to support you or experience (photos welcomed=]) to help others learn about VPD
 
Alienwidow

Alienwidow

Well-Known Member
Thorhax said:
ok you might be right... but your not talking about VPD. lets assume your have enough air flow to support the humidity. give me some actual talk on why you think that would b good or bad? with some science to support you or experience (photos welcomed=]) to help others learn about VPD
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Air flow wont help you. Lowering the humidity below 50 will though. Ive seen what high humidity does. Its not pretty. If the plant produces long banana like colas its more susceptible to mold from high humidity than popcorn style budding, but over 65% humidity and it will mold too. If anyone has their humidity that high theyre asking for problems.
 
Thorhax

Thorhax

Well-Known Member
Alienwidow said:
Air flow wont help you. Lowering the humidity below 50 will though. Ive seen what high humidity does. Its not pretty. If the plant produces long banana like colas its more susceptible to mold from high humidity than popcorn style budding, but over 65% humidity and it will mold too. If anyone has their humidity that high theyre asking for problems.
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I agree right now that high humidity is bad. But it works very well for large scale growers.
 
Sativied

Sativied

Well-Known Member
Such high humidity messes up a carbon filter so it's not for me regardless, but besides that, it's hard enough already to keep humidity low enough through all seasons and going through a year without budrot.

"The ideal temperature for [botrytis] infection is approximately 60–75ºF, although it can occur at temperatures outside this range under longer wetting periods".

Without additional control the high humidity of the day will drop slower (if any) than the temp, creating more optimal conditions for budrot. Actually started a breeding project to create a bud rot resistant variety, but even if that works out there's still the issue with carbon filters.

I'm happy if it stays between 40-60% during flower, and preferably on the low side of that the last 2-3 weeks. Before those last weeks though... (never had rot earlier than that) I could quite possibly benefit from raising humidity during otherwise hot dry days.
 
ttystikk

ttystikk

Well-Known Member
I run high RH. Powdery mildew isn't the bogeyman, it can easily be managed with natural and simple ingredients.

High RH encourages the plant to keep its stomata open, thereby increasing uptake of Co2.

Higher temperatures raise metabolism, encouraging faster growth.
 
T

The Nine

Active Member
Thorhax said:
but spores do not germinate under 75F so mold would never start.
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It's starts at the stem inside the bud where it is much cooler and then grows out. By the time one can see it, it's already well established.
High temps only work if the co2 ratio is increased accordingly.
High humidity is a recipe for disaster unless the plants have a lot of air movement and a lot of room for the air to flow around the plants.
For scrog and sog, low humidity is as important as air, light and water.
 
Thorhax

Thorhax

Well-Known Member
So with the right environment control having a temp of 80-85F and humidity around 70-85% would increase the plants metabolism and increase the transpiration rate?
 
Gquebed

Gquebed

Well-Known Member
Thorhax said:
So with the right environment control having a temp of 80-85F and humidity around 70-85% would increase the plants metabolism and increase the transpiration rate?
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I dont have enough experience to answer and id like to hear from somebody who does.

But... i do know that on my last run i was hitting 70% humidity with temps around 79/80 and i was getting explosive growth in veg. Once the plants got to around 18" tall humidity was hitting 80 to 85% and the plants stalled right out. So i cranked up the dehumidifier and brought rh down to 65ish and the growth quickly resumed.

I suspect there must be a saturation point....
 
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