# When to Stop co2 Increase During Flowering?



## Micobfsb (Nov 29, 2011)

Ive been reading alot lately and it seems like many people advocate stoping co2 enrichment durring the last two weeks of the flowering phase. I am wondering, why is this? If co2 helps the plant grow durring all of its other stages, why wouldnt you stop the enrichment right before you harvest the plant?


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## Micobfsb (Nov 29, 2011)

While we are at it, ive been reading that one is supposed to increase the temperature of plants while co2 enrichment is taking place, but some have said that this stresses the plants, anyone have any thoughts?


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## TrichomeTrent (Nov 29, 2011)

Micobfsb said:


> While we are at it, ive been reading that one is supposed to increase the temperature of plants while co2 enrichment is taking place, but some have said that this stresses the plants, anyone have any thoughts?


The reason for this is limiting factors. Co2/oxygen/light/nutrients/temp must essentially be balanced. If given numbers just for the sake of explaining, let's say you run all factors at '2', but then decide to increase co2 to '3'. To simplify the explanation the plants will still grow at '2' or only slightly faster unless you increase everything. Ed Rosenthal explains it in his book I believe


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## Micobfsb (Nov 29, 2011)

Thanks kindly, again, while we are at it, what about resevoir temp while co2 enriched?


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## TrichomeTrent (Nov 29, 2011)

Reservoir temperature is actually a pretty trivial detail. I would say as long as its not too cold or warm so it doesn't shock the plants or effect room temperature (if its large enough). Other than that just keep the water moving so it doesn't become stagnant or have nutrients settle on bottom. Will also deter alot of insects from laying eggs in your reservoir. 

Happy growin'


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## Micobfsb (Nov 29, 2011)

Thank you kindly


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## hempknightt (Nov 29, 2011)

Micobfsb said:


> While we are at it, ive been reading that one is supposed to increase the temperature of plants while co2 enrichment is taking place, but some have said that this stresses the plants, anyone have any thoughts?


Basically even if you have more CO2, if you dont have enough light/other factors to match the increase the plant wont make its sugar sandwiches or whatever they make to grow.

Im curious to know why people say to shut it off as well. It seems sortve like a myth, like the one about flushing your plants of nutes when it needs them the most.
(I think growers start these myths so that other people dont grow as good lol)


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## mvoltage24 (Dec 3, 2011)

i have always shut off my co2 off 2 weeks before but in recent weeks ive been doing research and im not doing that anymore. im letting it run till harvest. 
IMO those last 2 weeks are the most important to have co2 cuz thats the "swell" phase. im 6 weeks into flower will try to report back to see if it helps.


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## HerbalPrincess (Dec 10, 2011)

Temperature is proportional to the root mean square velocity of the molecules, be it the plant or the air. This means at higher temperatures the molecules are moving faster, and therefore chemical processes happen at accelerated rates, especially diffusion driven biological processes. Even the air molecules on the surface of the leaf are being replaced quicker at higher temperatures. Adding CO2 allows the plant to operate at this accelerated rate, transpiring water at a faster rate and therefore is able to cool itself better and handle the increased temperature. Its a process that goes hand-in-hand.

But then again that's all just speculation.


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## rabidnz (Dec 11, 2011)

and also higher heat = faster growth of any bacteria within the ranges we are using, whether mould on the plants or gunk in the res. Dont just go straight to the upper ranges of suggested temperatures without constant monitoring of plants and of course excellent humidity control.


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## 322special (Dec 11, 2011)

i do have the same questions. i was bout to do a post then found this..the guy at my hydro shop told me t run 1000 ppm during veg,switch to 1500 for flowering and right when the buds start to swell lower down to 500ppms. you lower to keep oil productions at it top game. this is what he told me,im trying to find similar search results...this c02 alone is like learning how to grow all over again..ive also read to keep temps higher than you would with out c02..any one else want to chime in?.....


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## moash (Dec 11, 2011)

I've read that keeping co2 on the whole grow takes the bud longer to mature
Thats why people stop 2 weeks before,so the bud will mature on time


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## HerbalPrincess (Dec 14, 2011)

After doing some more research, I learned that increased temperatures also allow increased CO2 uptake because at higher temps, the plants need to transpire more water to stay cool, so they open their stomata wider and therefore can get more CO2. Increased humidity also helps because it makes it harder for the plant to transpire, so once again the stomata open wider.


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## stondded (Dec 30, 2011)

i try to keep my cge setup between 78-82 when the lights r on
and i have always left my co2 run all the way up to harvest but i also run a perpetual setup
i have also heard tho tht when co2 is backed off or stopped the the essential oils for smell and taste r more pronounced
but i have tried to make up for running all the way to harvest by putting plants in dark for 2 days before the chop


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## delatour (Dec 30, 2011)

I think you should let it go to the bitter end if all other variables are correct it can only help co2 is never going to harm your plants. CO2 also does allow for higher temperatures but as another poster pointed out, with the increase in temperature you could also increase other problems. If your humidity is proper 40% to 50% relative humidity you should be ok though. Also nutrient solutions are best uptaken at 65 degrees, higher than that and less oxygen is getting to the roots. Co2 *does not *make plants take longer to flower it actually decreases flowering time while simultaneously increasing yield. It also helps plants thrive which keeps them heathier. Co2 is your friend inspite of what your government tells you.


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## delatour (Dec 30, 2011)

322special said:


> i do have the same questions. i was bout to do a post then found this..the guy at my hydro shop told me t run 1000 ppm during veg,switch to 1500 for flowering and right when the buds start to swell lower down to 500ppms. you lower to keep oil productions at it top game. this is what he told me,im trying to find similar search results...this c02 alone is like learning how to grow all over again..ive also read to keep temps higher than you would with out c02..any one else want to chime in?.....


 Running co2 only works in a vegetative stage if you are growing under a high intensity lamp. If your using fluorescents it's a waste of money.


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## kona gold (Jan 8, 2012)

I think the main reason people have said to stop using co2 the last two weeks of flowering is so the flowers stay dense and dont run or fluff at the end. Mainly i believe if you still have too much available nitrogen your plants will still be processing this, then having the co2 can cause unwanted late term leaf growth especially near the bud tips, which is not what you want to happen at end. If not much nitrogen available at end of cycle( nitrogen can also be stored in plant tissue with eccessive chemical ferts.), then should not be a problem. Good luck and aloha


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## kannibis (Jan 8, 2012)

delatour said:


> Running co2 only works in a vegetative stage if you are growing under a high intensity lamp. If your using fluorescents it's a waste of money.


No sir, you are wrong. I am not going to lay it out for you however. Go do some research and chime back in when your up to speed.


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## kannibis (Jan 8, 2012)

I personally run all the way up to the end. High nitrogen causes to much foliage (foxtailing). Stopping co2 right at the start of the swell is like making a car that shuts off half its cylinders when you press the accelerator to the floor, not very smart. Instead, stop the nitrogen, give it tons of PK and just a touch of N. If you notice, good growers are much more concerned with proper nutrient feed schedules than hoodoo voodoo techniques.


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## asilsweater (Jan 10, 2012)

From my own expierences co2,is used heavily in conjunction with humidity and 78 to 85 are ideal for veg and in first phase of flower ur co2 is shot up to 1800,2000 and temp 80,second phase of flower co2 is reduced to 600 ppms and temp reduced to 75 degrees,this helps keep trichomes from being affected by heat and last two weeks i keep co2 at 600 and reduce temp to 70,dis helps my flowers dense up and get sugary since they think winter is here,one thing i must say and dat is co2 will increase ur humidity,in veg its k and in early flower but in mid flower and late bloom u dnt want as much becuz it can lead to bud rot or mildew.dehumidifier is highly recommended!! Key to big flowers is high lumens,co2,good fert schedule and good genetics,


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## Thedillestpickle (Jan 10, 2012)

I just added this thread to my favourites list...

CO2 will not raise your humidity, if you use a CO2 generator(propane or natural gas burner) then yes your humidity will rise, but the same is not true for a CO2 ejector. 

During the last two weeks of flower its a good idea to lower your temperatures so that you dont volatize the very nice aromas of the bud. You can keep running them high for the sake of yield but for higher quality you should lower temperature to normal levels. Now that your temperatures are back at normal levels theres no need for the extra CO2. 

Flourecents can be used in conjunction with CO2 but only if you have alot of light, Usually if your running that much light you have invested in a HID, but some people will run alot of light using just flourecents. This myth is actually stated with no explanation in the growers bible by Jorge Cervantes, His book is alright but its full of misinformation

Hopefully Im not full of misinformation(bullshit), everything I just typed is speculation


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## IVIars (Jan 15, 2012)

By decreasing the co2 levels toward the end, i believe it stops ethylene (sp?) production and begins ripening it. 

Warmer temps when running co2, 80 and above.

Too much humidity cause the trics to become elongated and make it easier for them to snap off


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## xmatox (Jun 24, 2016)

kannibis said:


> No sir, you are wrong. I am not going to lay it out for you however. Go do some research and chime back in when your up to speed.


Lol. You're funny.


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## DirtyEyeball696 (Jun 26, 2016)

I use co2 all the way until the last 7 days of flower. The biggest thing to keep an eye on is the humidity. 45-50% is optimal


Kush is My Cologne


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## Dr. Who (Aug 2, 2016)

TrichomeTrent said:


> Reservoir temperature is actually a pretty trivial detail. I would say as long as its not too cold or warm so it doesn't shock the plants or effect room temperature (if its large enough). Other than that just keep the water moving so it doesn't become stagnant or have nutrients settle on bottom. Will also deter alot of insects from laying eggs in your reservoir.
> 
> Happy growin'


KEEP IT BELOW 70F or risk loosing everything to root rot!


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## Dr. Who (Aug 2, 2016)

Micobfsb said:


> Ive been reading alot lately and it seems like many people advocate stoping co2 enrichment durring the last two weeks of the flowering phase. I am wondering, why is this? If co2 helps the plant grow durring all of its other stages, why wouldnt you stop the enrichment right before you harvest the plant?


You stop at 2 weeks left so the ethylene gas _starts_ to be expressed by the plant to actually ripen the bud! It is connected to the bulking phase and if you don't stop it's use (CO2) the plant will take longer to actually ripen and it decreases the potential yield!

The use of CO2 in veg is NOT worth the cost of doing it! Sure your supplier is going to say to! He's the only one actually GETTING any "profit" from it!



hempknightt said:


> Basically even if you have more CO2, if you dont have enough light/other factors to match the increase the plant wont make its sugar sandwiches or whatever they make to grow.
> 
> Ah, kinda.....To use CO2 in any higher concentrations. You must have enough light intensity! To actually make the CO2 work at peak effectiveness, you MUST also increase the temp and RH on a bell curve! For 1500ppm to actually work right - you MUST have at LEAST 80,400 LUX of light!
> 
> ...


You read above right?

And you guys believe this SHIT! For god's sake you don't even go out and find the truth? Best info on this subject is in Ed Rosenthals book "Marijuana Growers Handbook" PAGES 131-142 and 192-193. 



mvoltage24 said:


> i have always shut off my co2 off 2 weeks before but in recent weeks ive been doing research and im not doing that anymore. im letting it run till harvest.
> IMO those last 2 weeks are the most important to have co2 cuz thats the "swell" phase. im 6 weeks into flower will try to report back to see if it helps.


Did you read everything to this point? DO IT!



322special said:


> i do have the same questions. i was bout to do a post then found this..the guy at my hydro shop told me t run 1000 ppm during veg,switch to 1500 for flowering and right when the buds start to swell lower down to 500ppms. you lower to keep oil productions at it top game. this is what he told me,im trying to find similar search results...this c02 alone is like learning how to grow all over again..ive also read to keep temps higher than you would with out c02..any one else want to chime in?.....


What crap! Running gas in veg is THROWING AWAY MONEY! 

GAS OFF FOR THE LAST WEEKS - Nothing to do with "OILS"....... YES! Higher temps and RH in bloom for gas to actually WORK right! I run 1300ppm with about 85- 87 F and 70-80% RH. You cool to normal at lights out. 



kannibis said:


> I personally run all the way up to the end. High nitrogen causes to much foliage (foxtailing). Stopping co2 right at the start of the swell is like making a car that shuts off half its cylinders when you press the accelerator to the floor, not very smart. Instead, stop the nitrogen, give it tons of PK and just a touch of N. If you notice, good growers are much more concerned with proper nutrient feed schedules than hoodoo voodoo techniques.


What the fuck? This is BULL SHIT of the highest order! Please list your source for this - I want to know!



IVIars said:


> By decreasing the co2 levels toward the end, i believe it stops ethylene (sp?) production and begins ripening it.
> 
> Warmer temps when running co2, 80 and above.
> 
> Too much humidity cause the trics to become elongated and make it easier for them to snap off


_EW, EW,,,,,SO close! "starts" the ethylene to become effective at ripening!_

_I might start at 80 F for 1150 ppm and have 85+F by 1300!!!_

_WHOOPSY! Wrong answer! You MUST run higher RH right along with the higher temps to maker the high ppm rates of the gas to BE effective!_


I hope you all read your personal answers!

Here is an example :

Your running, oh lets just say 1500ppm of co2 - to make the point here..
You have 5000 lumins of light (645w per square meter)
Your temp is 70 F 
The plant is only _up-taking or "using" 800 of those PPM!!!!_

OK, same set up BUT,
Your temp is 85 F
The plant is now up-taking _1300 of those PPM!!!!!!_

NOW THEN: A word on higher RH with gas use.

Alright then guys and gals Have you ever heard of the VAPOR PRESSURE DEFICIT?

I borrowed this for my ease - 

RH has an ever more direct effect on plants. Plants need to "sweat" too - or rather, they need to transpire (release water vapor through their stomata) in order to grow.

The amount of water plants lose through transpiration is regulated, to a point, by opening and closing their stomata. However, as a general rule, the drier the air, the more plants will transpire. 
RH has an ever more direct effect on plants. Plants need to "sweat" too - or rather, they need to transpire (release water vapor through their stomata) in order to grow.

The amount of water plants lose through transpiration is regulated, to a point, by opening and closing their stomata. However, as a general rule, the drier the air, the more plants will transpire. 

TAKE a LOOK at this chart!







Now while I run only 45% RH at say 75 F with NO gas.
When I run gas, I have to be FAR, far closer in the VPD for the co2 and plant work at it's best _together!

CO2 increases uptake. This means your getting more nutrient, right along with that water!
By this factor of increase (about 30%) you NEED to balance much closer that VPD to not begin to feed too much.
_
When I run my generator. I have a temp of 85-87F and an RH of about 70-75 during gassing hrs...

Understand this ?

PLENTY of scientific PAPERS available on the web to read on exactly this subject and it's parts described here!

Start looking!


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## Dr. Who (Aug 3, 2016)

DirtyEyeball696 said:


> I use co2 all the way until the last 7 days of flower. The biggest thing to keep an eye on is the humidity. 45-50% is optimal
> 
> 
> Kush is My Cologne



You better read the above post as punishment for duping me into answering a 4 year old post! You should find your RH is too low!


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## thewanderingjack (Aug 3, 2016)

moash said:


> I've read that keeping co2 on the whole grow takes the bud longer to mature
> Thats why people stop 2 weeks before,so the bud will mature on time


And thats a big yes because:



IVIars said:


> By decreasing the co2 levels toward the end, i believe it stops ethylene (sp?) production and begins ripening it.


Except not begins, allows to begin... CO2 inhibits ethylene production, a fruit hormone/pheromone that induces ripening and is produced by ripening plants. Transport trucks use low temps and CO2 to transport produce to reduce the risk of spoilage.

"one bad apple spoils the bunch" is a metaphor based on this literal effect.

p.s:. remove ripening fruit from other fruit, preferably completely away, to extend the other fruits life... a ripening fruit will ripen other fruit.



Dr. Who said:


> KEEP IT BELOW 70F or risk loosing everything to root rot!


*
If* you don't ventilate well in and around each plant... I run that high or higher (my environments very wet) and only have problems when I have overlaps or just not enough air circulation... both by pulling branches out via LST and by having a nice fan blowing. I just went through my plant super close... only problem I found was where a plant had had a branch up against the wall (just a small spot).


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## Dr. Who (Aug 3, 2016)

thewanderingjack said:


> *If* you don't ventilate well in and around each plant... I run that high or higher (my environments very wet) and only have problems when I have overlaps or just not enough air circulation... both by pulling branches out via LST and by having a nice fan blowing. I just went through my plant super close... only problem I found was where a plant had had a branch up against the wall (just a small spot).


You do know I was talking about DWC right?
One day you'll hit a strain that will NOT hit a 70F res temp without getting root rot. Can you say Bomb Seeds? That's just off the top of my head.......You do not allow res temps to go over 70 F....general accepted temp across the board....


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## thewanderingjack (Aug 3, 2016)

Dr. Who said:


> You do know I was talking about DWC right?


Hah, I did do and had forgot... so yeah... I should sleep... it's been a while.  I'm sure I was even referring to bud rot.

Root rot, in DWC, I know nothing about... but just to note: in soil, it is just as serious... most people in general, and newbs in particular, "over water" and wind up drowning their plants. 

Thanks for the heads up ... hate to be accused of talking out my ass (and having it be true!)


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## b4ds33d (Aug 3, 2016)

322special said:


> i do have the same questions. i was bout to do a post then found this..the guy at my hydro shop told me t run 1000 ppm during veg,switch to 1500 for flowering and right when the buds start to swell lower down to 500ppms. you lower to keep oil productions at it top game. this is what he told me,im trying to find similar search results...this c02 alone is like learning how to grow all over again..ive also read to keep temps higher than you would with out c02..any one else want to chime in?.....


the bro science is strong with this one.


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## powerslide (Aug 26, 2016)

2012 brought back to life to call some dude out and disappear. Nice


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## xmatox (Aug 26, 2016)

powerslide said:


> 2012 brought back to life to call some dude out and disappear. Nice


Disappear? He never responded to me probably because he was here for about a day and left. I did however bring back this thread from the dead. My B


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## D port Growth (Oct 11, 2016)

Dr. Who said:


> You stop at 2 weeks left so the ethylene gas _starts_ to be expressed by the plant to actually ripen the bud! It is connected to the bulking phase and if you don't stop it's use (CO2) the plant will take longer to actually ripen and it decreases the potential yield!
> 
> The use of CO2 in veg is NOT worth the cost of doing it! Sure your supplier is going to say to! He's the only one actually GETTING any "profit" from it!
> 
> ...


Schooled... he hit them with the VPD for the killshot.


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## organixx325 (Oct 13, 2016)

Dr. Who is the man, thank you for the input and correcting all the assumptions floating around. Just setup cO2, temp running at 85-88 above canopy and trying to get my RH up to 80%. I may need another fogger,


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## linky (Oct 15, 2016)

Dr. Who said:


> You stop at 2 weeks left so the ethylene gas _starts_ to be expressed by the plant to actually ripen the bud! It is connected to the bulking phase and if you don't stop it's use (CO2) the plant will take longer to actually ripen and it decreases the potential yield!
> 
> The use of CO2 in veg is NOT worth the cost of doing it! Sure your supplier is going to say to! He's the only one actually GETTING any "profit" from it!
> 
> ...



I just started my new room and have learned about VPD myself very recently. I am running mid to high 80's canopy temps and 1250 ppm of co2 with ~75 percent humidity. I am curious though how long in flower people are using the VPD chart, all the way through or only the first few weeks of flower? I am about 4 weeks in right now.

The first two weeks of flower I was unaware of VPD and was running mid to high 80's at ~50% humidity and 1500 ppm of co2, and the plants actually did not look good. I thought it was a nitrogen deficiency but after researching I think it was partially to do with VPD, to high temps and much to low humidity. Granted I am also running strains I have never grown and complete new hydro system and nute line.. so tons of my factors all at once.

Now that I think I have my environment doing pretty good I am just curious how long I should be running those temps and humidity, I am thinking the last couple weeks I should lower temps a bit and lower humidity to avoid bud rot. So far I have had zero issues with PM.


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## DirtyEyeball696 (Oct 18, 2016)

I run my co2 burner at 12-1500 ppm
It's awesome and makes my plants grow so much better. 85-95 degrees won't hurt your plants but make sure you have proper circulation 


Kush Is My Cologne


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## DirtyEyeball696 (Oct 18, 2016)

I'm not up much for charts, but I am interested in growers who use co2 & their input 


Kush Is My Cologne


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## Peter Vakomies (Oct 18, 2016)

If you have enough light to drive the 'extra' photosynthesis, always enrich with CO2, right to the end.

Just a few facts about plant physiology to consider:

All green parts of the plant, every green cell there is, are trying to fix CO2, and capture it and build the CH2O carbohydrate into the 'body' of the plant. Even green buds, stems and calyxes fix CO2 into CH2O's. The whole green plant is starving for CO2.

Remember - *45% of the dry weight of a bud is made of carbon, and it all came from CO2 in the air! * That's almost half of the dry weigh of our crops is carbon alone, so CO2 enrichment works; it will increase yield if you have high enough light levels.

The leaf temperature is always warmer than the air tempearture. 85 deg F in the air is 90-92 deg F on the leaves... To increase VPD, which makes plants transpire more, just cool to 70 Deg F with air conditioners. A 70 Deg air temperature is a 75 deg F leaf temp.

Cooling the air with AC's dries the air alot, so AC's pull the water out of the plants, the operating AC's are 'growing' the plants too!. Transpiration equals growth; the plant that uses 10 liters of water a day is growing bigger than the plant using just 2 liters a day. With unlimited water in the root zone, stomata are open, and CO2 pours into the plant.

Also plants always acclimate to a high level of CO2, they get 'lazy' and make way less RUBISCO enzymes if exposed to high CO2 levels all the time. This enzyme is the one that 'grabs' CO2 from the air; plants won't invest in making more RUBISCO if the CO2 level is high. This has been studied in detail, as RUBISCO is the most abundant enzyme on Earth; it enables all life!

Inside plant cells there are way more RUBISCO enzymes to take a 'gulp' of CO2 from the air if CO2 is running at 500ppm, than when plants have been growing at 1500 ppm CO2. These enzymes cost the plant to make, and their turn-over rate is fast, they aren't synthesized in the dark, and will even be broken down at night. In the day time plants make as much RUBISCO as they 'think' they need.

So if you vary CO2 levels between a low of 600 ppm and a high of 1200 ppm, more CO2 will be 'eaten' from the air by the plants as they will not get 'lazy' by synthesizing less RUBISCO enzymes. Turn on CO2 injection at 600 ppm, turn it off at 1200 ppm, and then let the crop suck the CO2 back down to 600 ppm before injecting more. 

The fastest growth by plants happens when they have unlimited water at their roots, and when the VPD is highest (ie 35-45% RH), combined with high light levels (ie PFD or photon flux density) at 1500-1800 umol (like the sun!), and they have dynamically enriched CO2 levels.

Combine this with ideal air temperature (75 Deg F) and balanced mineral nutrients, and the plants transpire like crazy, fix CO2 like mad as light drives the 'engine' of photosynthesis at full speed, and you get maximum yield.


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## DirtyEyeball696 (Oct 18, 2016)

Peter Vakomies said:


> If you have enough light to drive the 'extra' photosynthesis, always enrich with CO2, right to the end.
> 
> Just a few facts about plant physiology to consider:
> 
> ...


I have 12- 1000 watt lights & 2 aprilaire 95 pint a day dehumidifiers in a 20x20' room. What would be an optimal temperature to run co2 in your opinion. I have a hydrogen co2 generator so it's watercooled. 


Kush Is My Cologne


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## linky (Oct 18, 2016)

35-45 rh is way to low, especially if you are going by vpd chart, with mid to high 80's leaf temp you should be at ~75% humidity.


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## DirtyEyeball696 (Oct 19, 2016)

Ok got a question what is a good temp to maintain 45-50% humidity consistently 
I'm noticing when the lights go off it seems to rise. I have my temp set at 73 when they go off. Should I raise it to 75 maybe?


Kush Is My Cologne


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## organixx325 (Oct 19, 2016)

I think your best bet would be to add a dehumidifier or at least some ventilation to move the air around at night.


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## DirtyEyeball696 (Oct 19, 2016)

I have 2 Aprilaire 90 pint a day. Everything seems ok until the lights go off and it seems to raise so I was wondering if I raised my "lights off" temp it might make my dehumidifiers. Maybe 75 degrees.


Kush Is My Cologne


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## Rasta Roy (Oct 19, 2016)

DirtyEyeball696 said:


> I have 2 Aprilaire 90 pint a day. Everything seems ok until the lights go off and it seems to raise so I was wondering if I raised my "lights off" temp it might make my dehumidifiers. Maybe 75 degrees.
> 
> 
> Kush Is My Cologne


Exhaust that air out of your room when your lights click off fam!


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## Rasta Roy (Oct 19, 2016)

Dr. Who said:


> PLENTY of scientific PAPERS available on the web to read on exactly this subject and it's parts described here!
> 
> Start looking!


You're the man for that post. Co2 use (like everything in the cannabis community) is full of misinformation even though there's good information out there.


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## DirtyEyeball696 (Oct 19, 2016)

Rasta Roy said:


> Exhaust that air out of your room when your lights click off fam!


Still kinda confused on the temperature to run when the lights are off so the dehumidifiers stay on properly. Like I said when the lights go off and temps drop I have my thermostat set to 73, should I go maybe 75 to ensure proper dehumidification? I have whole home dehumidifiers not small single ones. They are set up a little differently 90-95 pints a day X 2 is ample for my 20 x 20. Just kinda confused not on the co2 part cause I have an automatic controller but more on nighttime temps to keep RH 45-50
If I'm in the wrong forum let me know
Thanks


Kush Is My Cologne


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## organixx325 (Oct 19, 2016)

I use humidity controllers to control humidifiers/dehumidifiers. Set it to to whatever humditity you want it to kick on and have it exhaust out when it reaches the set humidity.


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## Peter Vakomies (Oct 19, 2016)

Even at night I use 72 deg F, and keep the dehums' going.

I like to keep things cool - The AC's dry the air so well, I like to keep them working hard to increase VPD. Are your dehumidifiers able to keep up ?

CO2 will get into the plant easily if the plant has no water stress, so I keep roots wet and I don't let air get warmer than 78 Deg F.

I'd set the AC's to run at 72 deg F, expecting leaf temps to be 77 deg or so in the day. If your dehum's discharge heat into the grow room, that will also trigger the ACs to run more, and together they'll just wring the water out of the air!

With a big crop I like to see the %RH of the air around 45-50% after irrigating, and I let it go as low as 30-35% before watering, but the soil is always wet. I usually water when the soil has dried to 70% of saturated (measured by the weight of a freshly watered pot= 100%). If roots run out of easy-to-absorb water, growth slows or stops; keep the soil wet !

With dry air and wet roots, plants transpire more, which equals faster and bigger growth. I usually set dehumidifiers to run until 40-45%RH. If you capture the AC and dehum' condensate, it's not unusual to irrigate with 1000 liters one day, and have almost 1000 liters returned to the reservoir within 24-36 hours.

It's true that the enzyme RUBISCO operates faster at warmer temperatures, but letting air temp rise to promote stomatal opening for cooling the plant often increases the air's humidity (lowers VPD). To enable the best use of CO2 we just want to keep the stomata wide open, so avoid any drought or water stress.

In contrast to RUBISCO's preference for warmer temps while it captures CO2 and makes carbohydrates, the photochemistry part of photosynthesis where chlorophyll is catching photons actually runs better at cooler temperatures. The green photosynthetic membranes in chloroplasts will overheat in high light and are constantly trying to dissipate that heat, so I like to keep air temp on the cool side. 70 - 72 deg. F, and keep the CO2 levels between 600 to 1200 ppm.


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## DirtyEyeball696 (Oct 19, 2016)

Peter Vakomies said:


> Even at night I use 72 deg F, and keep the dehums' going.
> 
> I like to keep things cool - The AC's dry the air so well, I like to keep them working hard to increase VPD. Are your dehumidifiers able to keep up ?
> 
> ...


Ok thanks 


Kush Is My Cologne


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## vilify (Oct 21, 2016)

my best results came from starting around 1800 ppm the first two weeks and lowering 200-300 every week.


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## Scottmurphy12 (Jun 28, 2019)

Peter Vakomies said:


> If you have enough light to drive the 'extra' photosynthesis, always enrich with CO2, right to the end.
> 
> Just a few facts about plant physiology to consider:
> 
> ...


Would you suggest exhausting


Peter Vakomies said:


> If you have enough light to drive the 'extra' photosynthesis, always enrich with CO2, right to the end.
> 
> Just a few facts about plant physiology to consider:
> 
> ...


What's your thoughts on co2 inhibiting ethylene production late flower, atmospheric levels during ripening phase?


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## guitarzan (Aug 4, 2020)

I just bought an ExHale Co2 bag...I have two plants that are near ready, already Final Flushed them and plain pHed water...I was planning on leaving the bag hanging until they're finished...kinda on the fence with thiis though.


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## Renfro (Aug 4, 2020)

guitarzan said:


> I just bought an ExHale Co2 bag...I have two plants that are near ready, already Final Flushed them and plain pHed water...I was planning on leaving the bag hanging until they're finished...kinda on the fence with thiis though.


Well lemme guess, you are using a blower to ventilate your space for cooling purposes? If so, the CO2 is exhausted faster than it's produced.


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## Terpenefiend (Jul 14, 2021)

That high of humidity is causing me anxiety and my monitor and controller won’t even be here until tomorrow. I am now contemplating just send the fuckers back. What’s the point of an increased yield if the chances of losing it to bud rot is that high?


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## AlexQc (Jul 30, 2021)

linky said:


> 35-45 rh is way to low, especially if you are going by vpd chart, with mid to high 80's leaf temp you should be at ~75% humidity.


ambiant humidity at 40-50% will reach easily 60-70% humidity when burst of transpiration of the plant occur you both are right but doesn't calculate the same humidity factor ...


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## TeW33zy (Mar 1, 2022)

TrichomeTrent said:


> The reason for this is limiting factors. Co2/oxygen/light/nutrients/temp must essentially be balanced. If given numbers just for the sake of explaining, let's say you run all factors at '2', but then decide to increase co2 to '3'. To simplify the explanation the plants will still grow at '2' or only slightly faster unless you increase everything. Ed Rosenthal explains it in his book I believe


WHAT? No no no. The reason you don't run co2 during the last 2 weeks is because of the Ethylene the plant produces to ripen your flowers. Ethylene is a hydrocarbon gas that plants produce at the end of there life cycle to ripen. If you run high levels of co2 while the plant produces Ethylene c2H4 it effects the hydrocarbon compounds. Ethylene has 2 carbon atoms and 4 hydrogen atoms which work together to ripen. This process is undergoing 4 types of reactions - oxidation, polymerization, halogenation, and hydration which is how you buds get that ripen look and oils.

You never want to affect the Ethylene ripening process, literally 2 gases in high concentrations effect each other. Co2 goes up, Ethylene stays down, Ethylene goes up, Co2 goes down, never ever up at the same time. No different than you guys putting a boveda 62% humidity pack in the jar during the sweating process, u never ever do that. You burp the jar until the jar consistently stays at 56-60% then after its stable a few days later u add the boveda pack so it's not affecting the sweating process. If you run extra co2 while the plant is producing Ethylene c2h4 your plant will literally not ripen correctly and you will have decreased quality, decreased oils, terpenes and everything. Don't do it.

I hope this helps.

~ Sr. Quality Engineer, M.S, (Medical)


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## calvin.m16 (Mar 5, 2022)

co2 enrichment only needs to be stopped when lights are off. I've noticed no benefit to turning off co2 late bloom.. If your co2 was to shut off the best time would be late bloom though, any other time the plants will be consuming much more of it. When I first flip plants into 12/12 my co2 burner runs a lot more than usual for the first few weeks during stretch, then it kinda slows down and isn't kicking on as much. Late bloom it only runs a few times here n there.. That is how I know at least.. Basic observation over the last couple years of using co2.

p.s don't run co2 higher than 1500 PPM anything higher and your starting to actually cause plants to reduce transpiration and close their stomata due to being enriched with co2 heavily. Keep your co2 ideally in the 1000-1200 range for the best results. I see some new to co2 people running it at insane levels like 2000-2,200, at those levels it can actually have an adverse effect.


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## Kassiopeija (Mar 5, 2022)

so when CO2 intake wears down I take it that means the photosynthesis rate slows down, too. which would warrant to reduce light influx, isnt it?


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## Samwell Seed Well (Mar 5, 2022)

Kassiopeija said:


> so when CO2 intake wears down I take it that means the photosynthesis rate slows down, too. which would warrant to reduce light influx, isnt it?


Funny how the plant tells you.. as its finishing its cycle

Eats less, transpires less...
To OP
Plants do all the work, just pay attention and open and close the right doors


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