Help me figure out what vpd i need with Co2! Please!

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RCJR

Active Member
So, in my flower room i have (4) 700watt led lights that are over 8 large plants (gotta grow them big due to numbers restrictions). I have different stages of flowering plants in this sealed grow room that i have 1200ppm of co2 in. I have a mini split and a big dehumidifier so i can dial in the vpd im after. However i get all kinds of conflicting info on what my temps and humidity should be. So i need your help!
My leaf temp is ruffly 2 degrees cooler than the room air. So a vpd chart (pic) with that leaf offset says ill be fine at 82f and 55% humidity. But im getting people telling me thats wayyyy to hot in flower. I also read that co2 at 1200ppm you should be running in the 80s. What should i do?
 

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Billy the Mountain

Billy the Mountain

Well-Known Member
RCJR said:
So, in my flower room i have (4) 700watt led lights that are over 8 large plants (gotta grow them big due to numbers restrictions). I have different stages of flowering plants in this sealed grow room that i have 1200ppm of co2 in. I have a mini split and a big dehumidifier so i can dial in the vpd im after. However i get all kinds of conflicting info on what my temps and humidity should be. So i need your help!
My leaf temp is ruffly 2 degrees cooler than the room air. So a vpd chart (pic) with that leaf offset says ill be fine at 82f and 55% humidity. But im getting people telling me thats wayyyy to hot in flower. I also read that co2 at 1200ppm you should be running in the 80s. What should i do?
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I wouldn't change anything.
Your conditions are ideal.
 
Beeswings

Beeswings

Well-Known Member
That's not to hot for early and mid flower, might be burning off terps come late flower though.
 
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RCJR

Active Member
Kola_Kreator said:
Don't. There's no need to dial back CO2
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I was doing some brief research and i can't find any scientific research on why dialing the co2 back during the last few weeks of flower is beneficial. It's probably bro science lol. But i have different stages of flowering plants in there so i have to set the room at a good medium for all the stages of flower.
 
Billy the Mountain

Billy the Mountain

Well-Known Member
RCJR said:
I was doing some brief research and i can't find any scientific research on why dialing the co2 back during the last few weeks of flower is beneficial. It's probably bro science lol. But i have different stages of flowering plants in there so i have to set the room at a good medium for all the stages of flower.
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Something to do with ethylene iirc.
I've done it both ways, ambient, or leaving CO2 at ~ 850 ppm
No difference I could discern, either yield-wise or quality.
 
K

Kola_Kreator

Well-Known Member
RCJR said:
I was doing some brief research and i can't find any scientific research on why dialing the co2 back during the last few weeks of flower is beneficial. It's probably bro science lol. But i have different stages of flowering plants in there so i have to set the room at a good medium for all the stages of flower.
Click to expand...
I received some advice from a large commercial grower to reduce everything for the last 2 weeks of flower. I think this helps them mature on time instead of continuing to throw white hairs.

But I also have plants in different stages of flower. Reducing the ppfd is known to help them mature and dropping the CO2 down to 850 is probably a good move too.

I am also still learning and experimenting with the best way to set up my sealed grow room. It's a big learning curve. I know a few guys that will run 1 plant per 600 watt led and they are pulling 2.5 + pounds consistently from each light with 5 weeks veg. Growing with optimum VPD and CO2 really let's you push what's possible.
 
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Delps8

Well-Known Member
@Billy the Mountain called it.

RIU has a great acronym "LTFA" but… (there's always a "but", right?)

The only discussion "in the literature" I've seen on lowering temp is research by Mitch Westmoreland, a Bugbee student, who discusses temperature and the impact it has on cannabinoids. The attached video provides excellent insight into a few topics — very much worth the hour it takes to watch.

If I were growing, I'd drop my ambient temps, and increase PPFD to 1500 or so and that's primarily because of the research that Westmoreland discusses in his video but also because of the research in the attached Frontiers paper.

In short, both researchers clearly state that, assuming that light is the contraining fact, cannabis will grow in ambient CO2 at light levels approaching 2kµmol. Yeh, that got my attention - 2k in ambient CO2. The highest I've gone is 1150± so 2k is WTF. OTOH, if you're in CO2, ≥1200 should be a walk in the park.

I've also uploaded the Chandra paper which deal with temp and CO2. One limitation of Chandra is that it deals with net photosynthesis and the data were captured by measuring gas exchange of a few leaves. Accurate, yes. Useful? Meh. My qualm with Chandra - I'm not harvesting net photosynthesis.

The Frontiers paper addresses those two issues and goes to the heart of the matter — how is yield affected.

Both good reads but the Frontiers paper takes the cake.

HTH.
 

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