Vpd At 18+?? I Don't Believe It

Ignignokt · Jul 28, 2016

I was researching UV for cannabis when I came across the oldest references regarding cannabis that were specific about OG hash plants from that part of the world. Afghani hash strains are indeed from the mountains there - high mountains at that.

I think we should be specific about what we mean by temperature (should be canopy) and how it is measured. Temperature of the room makes a great bulk measurement - however it is not the temperature of the canopy.

Douglas.C · Jul 28, 2016

GT21 said:
Well considering VPD was originally studied on populus candicans in 1978 i think ...weed growers read a bit too far into it. Vpd and trich production do NOT go hand in hand.... this is like saying because i can hold my breath longer then i can get also get a great tan hahaha. Trich production and terpenes are a defense response to harsh climates. The dryer the air the more oil the plant will make... the stronger UV the more the plant will flip out trichs to block the rays.

This matches my research as well.

I do like the extra UV I get from open hoods. :) I've noticed that making a difference, yes.
High terpene/cannabinoid cannabis is simply awesome!

Douglas

Douglas.C · Jul 28, 2016

Ignignokt said:
I was researching UV for cannabis when I came across the oldest references regarding cannabis that were specific about OG hash plants from that part of the world. Afghani hash strains are indeed from the mountains there - high mountains at that.

I think we should be specific about what we mean by temperature (should be canopy) and how it is measured. Temperature of the room makes a great bulk measurement - however it is not the temperature of the canopy.

Doesn't surprise me in the least about afghanistan. :)
That's been a confusion, yes. I always talk canopy temps. When I talk about room conditions, you'll see me use the word room. :) Just a heads up from my side.

Douglas

Ignignokt · Jul 28, 2016

Douglas.C said:
Reality does not bear this out though. Same light, same nutes, upside down VPD with high humidity and temps and the same clone comes out VERY differently.

One comes out like the majority of cannabis I come across, aromatic but nothing special. The cannabis grown with 25% humidity and 72F temps, under the same light, grows significantly more trichomes and retains significantly more terpenes. Massive difference in aroma and flavor intensity.

Douglas

And that is the calculus of steering phenotype expression! For any strain there are typically multiple phenotype expressions awaiting your misadventures and mistakes to discover (usually at a disappointment). We are hunting for the sweetspots for our various strains - so indeed your mileage can and will vary. Unless you monitor and measure all the variables and somehow control them - some variations are practically guaranteed. And I think the challenge of it is a new sport with a cup envied by many.

Iggy

GT21 · Jul 28, 2016

Ignignokt said:
And that is the calculus of steering phenotype expression! For any strain there are typically multiple phenotype expressions awaiting your misadventures and mistakes to discover (usually at a disappointment). We are hunting for the sweetspots for our various strains - so indeed your mileage can and will vary. Unless you monitor and measure all the variables and somehow control them - some variations are practically guaranteed. And I think the challenge of it is a new sport with a cup envied by many.

Iggy

Oh now were talkin allele frequencies... thats a whole new thread in itself hahaha

Douglas.C · Jul 28, 2016

Ignignokt · Aug 14, 2016

I came across this today -

I think this is perhaps the best explanation I've seen for a sudden appearance of PM. I no longer use any direct ventilation on my plants - the fans that create turbulence in the tent and the dehumidifier are behind a reflective barrier about 48" high. I have one high capacity fan that points to the top of the tent from that area - to disperse cooler air and CO2. I get great air movement and mixing without the leaf cooling from direct draft. I suppose this may be because of the lower canopy temps generated by my remote Phosphor LED lamps. I found the more direct ventilation - the worse the PM issues become. When I first used these lamps - it was a sealed room rather than a tent and I used this partitioned area for circulation. I had no PM issues whatever even when I had condensation on the walls. When I moved to the tent - I didn't use the partition and the plants got drafts. And PM.

I get data (CO2 ppm, Temp, Humidity, DewPoint) every 10 seconds that I record from an Ampro CO2 meter. Having the ability to monitor dew point has been useful to derive VPD - a calculator that will give vapor pressure from dew point is here -

Douglas.C · Aug 14, 2016

Why are growers under the impression High VPD always means high humidity?
I grow the opposite, high VPD, low humidity environment.
High VPD, Low Humidity
Another Study using High VPD, Low Humidity
Here are the results of the VPD calculator you posted (thank you)

These are freely available studies, I can imagine there are tens of thousands more studies using high vpd, low humidity environments as a control or other part of their study.

I see your point with the airflow. I generally only have fans below the canopy, blowing up through. Since my incoming air is around 68F, it reaches around 72F at the top of the canopy, as it heads up toward the exit. Only the lower canopy gets that direct air movement, so along the same lines.

Good job. :)

Douglas.C · Aug 14, 2016

When plugging in values of 82F, 70F, the dew point is 71.2. Saturated VPD is 37, 11 points higher than my low humidity conditions. So it's actually higher than 18, at 36.

The 71.2F dewpoint is scary. Anything quits and you're looking at a huge dump of humidity on everything in the room.

I see why most folks go with upper 70's and 40-50% humidity instead. Not only is it significantly easier to achieve/maintain, it keeps transpiration high through both cooling and hydration usage.

Purpletrain · Aug 14, 2016

People have been doing it wrong when it comes to humidity and plant stages
they think once in flower you need low RH this is far from the truth , If we look at nature how does it all work in stages think about it april showers high humidity 80's seed birth in summer in the 60 - 70 's fast vegetative growth as the sun clock starts the flowering cycle RH does not drop to 30's its a slow progress downward just like light hrs slowly drop each day
Follow these guide lines, meaning once in flower slowly drop RH as weeks go by i keep 60 RH up to 4th week of flower then i start lowering it people all think UV is the only thing that triggers plant protection ,, this is also far from the truth /temps are more crucial and like fall like temps it slowly drops apply this to your grow and watch the superior results
again as you get further n flower drop temps as well i have grown indoor weed to near freezing temps root zone is warm but ambient temps is cold par is there what happens
transpiration and respiration is rather key to plant nutrient up take
Its all about smooth transformation not sudden drops in RH this is why you see so many issues in flowering stage
here is a example morning frost on buds :) mind you first frost i never harvest until second frost then picture 2 hrs later ) plants not dead there growing and let me tell you it was killer weed
Jedi growing at its finest

Douglas.C · Aug 14, 2016

Purpletrain said:
People have been doing it wrong when it comes to humidity and plant stages
they think once in flower you need low RH this is far from the truth ,

Is cannabis a trichome bearing plant? Yes.
Is it a plant who's trichome density is controlled by humidity? Yes.

Do you get higher terpene production and retention with low humidity? Sure seems like it to me. Eventually I'll be able to pay for lab tests. Unless someone can point to a side by side and lab tested the results.

I'll take low humidity, low temp grow rooms any day. The terpene production is amazing, it's much more comfortable and I have zero issues with mold.

Purpletrain · Aug 14, 2016

Lets be honest with our selfs there are many things the influence trich production on any strain
one being gentic profile or make up of strain lets face it some strain produce as others do not your claim is that even low producers would work in that enviroment

Yes enviroment plays a huge roll in terp production but so does PPFD light intensity altitude
there is a lot that needs to be addressed and its all important also
I think anyone wanting the best they can get out of there plant or strain is understanding where the strain originated from study the climate
For instance PPP plant Africa strain i studied relative RH, temps, wind factor from this area implemented it into my grow room and WOW

Douglas.C · Aug 14, 2016

Purpletrain said:
Lets be honest with our selfs there are many things the influence trich production on any strain
one being gentic profile or make up of strain lets face it some strain produce as others do not your claim is that even low producers would work in that enviroment

Yes, even low producers are maxxed out to their genetic potential. Every single strain I've run, for 15 years has come out more trichome dense. More trichome dense, compared to the same genetics in other gardens with high humidity.
Higher terpene retention as well. Again, going solely on the massiveness of aroma/flavor from my garden, vs. others. (though clean growing has a lot to do with that as well.)

I believe cannabis has core genetic triggers and it doesn't really matter where on the planet it came from. At least it doesn't matter when you're shooting for extreme quality. I highly doubt there's a single spot in nature where cannabis automatically grows superior quality.

It's a hyper/dynamic accumulator and nature does not supply the correct feed levels and cyclic pH ranges to extract extreme quality. Every strain responds to the environmental triggers the same way, the only difference is in their individual expressions. The individual expressions are minor, to the impact of environment.

Douglas.C · Aug 14, 2016

Very nice photos, btw :D

Homesteader · Aug 14, 2016

Douglas.C said:
I'll take low humidity, low temp grow rooms any day.

The electric company thanks you

Douglas.C · Aug 14, 2016

Homesteader said:
The electric company thanks you

Yeah, sucks that higher quality requires more electric. I'll pay it any day. :)

Homesteader · Aug 14, 2016

Possibly but I have been running 85 degree leaf temps with higher humidity under LED and haven't found the need to get either lower. Fuck the power companies.

Douglas.C · Aug 14, 2016

Homesteader said:
Possibly but I have been running 85 degree leaf temps with higher humidity under LED and haven't found the need to get either lower. Fuck the power companies.

Unless you previously had experience with the opposite, of what value is your data here?

Homesteader · Aug 14, 2016

Bought the same value as yours I would say, or are you just looking to be a tough guy?

GT21 · Aug 14, 2016

Douglas.C said:
Unless you previously had experience with the opposite, of what value is your data here?

I have grown in florida and Arizona... omitting water tables ill take 0% humidity over 99% humidity any day. Both places hit 100f no problem. STOMA ADAPTS .. why im not a fan of that chart hahahah

Vpd At 18+?? I Don't Believe It

Vpd At 18+?? I Don't Believe It

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