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

[Douglas.C]

Nice and frosty, what's the strain? :)

Yeah, not a big fan of humidity or high temps. Stomata adapts, still stresses the plant. No, I've only grown in high humidity once, and that's back when I didn't know anything. Other people around me all grow in high humidity, high heat. The difference in the genetics is so great, you can't tell they're both flowers from the same clone.
I'm looking forward to doing a few side-by-sides myself, so I can document the difference.

I'm MUCH less picky about environment when I'm looking to do extractions.

 

[Purpletrain]

Way i look at it is find the happy medium where plants excel in growth yield and final product
There is no cutting corners other then experience , we all may think one way is better then another but at the end of the day mother nature works in mysterious ways ,,
And were infants in that area of understanding with have hypothisis but even in science what was once thought to be true is changed n a heartbeat

 

[Douglas.C]

When you get the same results with nearly any genetics, not just ones touted as 'elite' for their frost, you know you're doing something correct.

At the end of the day, it's all about soft, cool, aromatic and delicious smoke. I like the fact resin drips from the end of the joint, with nearly any strain I grow.

 

[GT21]

When you get the same results with nearly any genetics, not just ones touted as 'elite' for their frost, you know you're doing something correct.

At the end of the day, it's all about soft, cool, aromatic and delicious smoke. I like the fact resin drips from the end of the joint, with nearly any strain I grow.

Bingo!!!! Hahaha i quit looking for good strains a long time ago... i just grow them all good lmao. .. thats SWEET LUCY by NWG

 

[Ignignokt]

Vapor Pressure Deficit - orange = ideal, white = acceptable, light blue = too humid, dark blue = too dry

This gives us a guide for the control band required at various temperatures. Unfortunately in practice you can only target a humidity level - good luck with controlling humidity with any accuracy. None of the consumer dehumidifiers have very good or accurate sensors for controlling the compressor.

What I think then is an algorithm can be derived to control what can be controlled (most likely temperatures) to automate the maintenance of these ideal conditions. The necessary bits for reliable automation have become cheap. I'd think this is probably the secret sauce in the industrial control systems - a green house has similar issues with changing conditions.

Reverse engineering is a hobby I really enjoy. Why buy when I can build ??? I figured out how to use a portable AC for a cool air source, If I can figure out the IR remote codes for the thing - I could adjust temps and fan speeds. I already found a suitable fan for computer control -

http://www.hyper-fans.com

These are true adjustable speed fans - the remote fob is simply a variable resistor - a potentiometer - that can be replaced with a silicon potentiometer. Zero Ohms is the slowest speed - ~5k Ohms is max. I'll be working on integrating the Hyperfan with the computer over the next couple of weeks.

 

[Douglas.C]

Vapor Pressure Deficit - orange = ideal, white = acceptable, light blue = too humid, dark blue = too dry

Yeah, that chart is wrong. Moving along.

 

[Ignignokt]

How is the chart incorrect ? I think it makes your point about high VPD of 18+ ( wondering where someone is taking measurements ) not making sense.

 

[Ignignokt]

My experience with running low (~30%) humidity is a significant increase in transpiration and nutrient concentration (salts formation in drainage) . I'm listening to your argument on ideal cool, dry conditions (as found in high elevations) for higher quality - I'd suppose I'd just like to see raw environmental data that somehow makes the point. For one, I'm skeptical of absolute rules. Also - the requirements for vegetation are different than for flower. I think your advice leans heavily to flowering. ( correct me if I'm incorrect ).

My grow is in a tent inside an outbuilding. The only real climate control I have is a dehumidifier and 8k BTU of cooling, so I have to deal with fluctuations. I'd like to understand it well enough in that environment that I could also apply lessons learned to a greenhouse of my own design with automated controls.

 

[Ignignokt]

I started to wonder why you didn't seem to be concerned about this - and then I finally checked your profile. You run DWC. I use Canna Coco in 12 inch net pots. I also grow in containers outdoors - mostly soil and a couple Coco to keep it interesting outside.

This changes things a bit, at least in regards to how I would evaluate your opinions on the subject. In DWC - you have built in methods to deal with nutrient consumption and balance. The root health issues are different - and you need to control temp anyway ( keep at 70 or bust! ) just keep them from going septic. The issues of salt buildup from rapid transpiration are dealt with in bulk by solution changeout.

I get only one shot at each watering - and its like artillery - you move toward what you think is the sweet spot, then fire for effect.

I plan on giving DWC a whirl - perhaps this winter.

 

[Douglas.C]

You need higher root zone temps than 68F for coco, silly. No wonder you had issues with salt buildup and unhealthy transpiration.

 

[Douglas.C]

fwiw, I've run all kinds of hydro and I have yet to have 'salt buildup.' Including coco. Granted I've always used the same nute formula and res management methods, according to the type of hydro.

 

[Douglas.C]

Funny you mention sealed rooms, I've been looking forward to finding optimum quality levels for CO2 as well. Not having had the funds for a sealed room, yes, my yields suffer from that. Good point. :)

I've grown many ways, the majority just happen to have been in dry environments. Nearly all the cannabis I sample from other people comes from high humidity rooms. You don't always have to do something yourself, to observe the difference from others.

Excellent writeup. Though I had a hard time with the formatting, it was well written enough to keep my interest through the entire thing. :) Well done. Very astute observations on the differences in plant structures vs. strain and environment. Additional information I look forward to documenting. :)

Thank You

 

[epitome]

The way I perceive VPD is that it's a marker, if you will, a reference point using vapor pressure defecit, not an instruction or a guide....ya dig? For instance genetics acclimated in equatorial environments will be one VPD and genetics acclimated to Hindu kush range would be a DIFFERENT vpd, know one vpd better then the other....yall follow?

 

[Ignignokt]

You could always give my Raspi CO2 monitor a go - Post #19

https://www.thcfarmer.com/community/threads/technologists-that-build-their-own-systems.82730/


I use 1200-1500 ppm. I use it during veg-stage to get robust growth for weeks 3-5 - thicker stems and really awesome sun leaves (as big as I've seen on my outdoor grows). I don't use it again until the second week of flower for a week - at that point I'm trying to help with the stress of the flip. And then again for the last two weeks before harvest.

I think another factor is a pretty dramatic difference between locations. I'm familiar with the typical humidity levels in the Mountain states ( mostly Idaho ) humidity levels are naturally pretty low. When I go there, I have to make sure I hydrate my guitars - while here near the coast it's almost always 50% or so. Getting low humidity essentially for free is a benefit of your particular location. In my case, it adds significant cost to control humidity. I need to understand how to get balance - VPD as a data point allows better control for my circumstance. The weather here is better for growing redwoods than cannabis it seems.

As for root temperatures - I think I need to move to a more frequent watering schedule. I've been hand watering - I'd like to automate that part as well, but the other automation has taken priority. That is part of what makes DWC attractive to me - keeping moisture and nutrients available without the variability of me getting around to do it manually.

 

[Ignignokt]

The way I perceive VPD is that it's a marker, if you will, a reference point using vapor pressure defecit, not an instruction or a guide....ya dig? For instance genetics acclimated in equatorial environments will be one VPD and genetics acclimated to Hindu kush range would be a DIFFERENT vpd, know one vpd better then the other....yall follow?

Agreed.

I've watched dew point for months now - I get a sample that looks like this every 10 seconds. This was during Veg.

Current Level: 1347 ppm Status:online Temp= 78.3 F Humidity= 50.6 % Dewpoint= 58.4 F Fri Apr 15 08:14:25 PDT 2016

The air temperature is not really that high as that particular sensor is internal to the CO2 sensor and is intended for temp compensation of the CO2 measurement - the nature of the device operating temp some 3-4 degrees above ambient due to IR LEDs used for the NDIR method.

 

[sumerianak]

the vpd chart felt wrong all the way through for me, as soon as i hit + 65% rh my plants started cupping and going nuts, i tried to raise my 78F temp to 81-83-85 during a week without any relief, as soon as i brought my rh down 40-50 the plants bounced back within 12 hours.. mind you, this was during the veg, i run in 7g soil pots. my flower room is a steady 80-85f with a 50% rh, i'm looking into lowering it as i get further into the bloom, a steady decline in % each week. problem will arise when we go further into fall, the humidity will have peaks of 70-80%, best bet here might be to connect the intakes to the outer room instead of the yard. so as i understand it, the best veg % is 50-60 rh with a 78f lights on and in flower 30-40% rh with 75f? i read somewhere that buds grow fluffy when temp gets over 85, that true? below 75f the plants get stupid and stunted? anyone in the know, please enlighten us with some % wise in regards to temp and rh during the different stages of our plant as this is really confusing. there is a big difference when you run a sealed room compared to a regular room where you draw in fresh air from the outside and dumping air in a horizontal arc with our outtake fan as i'm doing atm. i have a good negative pressure in there also, that's good right?

 

[Savage Henry]

I recently switched a room from sealed to negative pressure and the rh is a steady 50-55% with temps maxing out around 80, but typically around 77. These have done as well as when I was running 83-86 degrees, 70% rh and co2 sealed up. Same strain, medium, ferts.

Edit: so, maybe the negative pressure of the air has an effect on the plants stomata.

 

[Ignignokt]

Leaf taco is the plant pushing back on the environment due to excess light or other similar stress that requires the stoma to close. Curious.

It should be noted - Higher temperatures used with CO2 (~85degrees) are due to the natural selection embedded in most plant genetics from a stress long ago. The stressor was the Paleocene–Eocene Thermal Maximum (PETM). When you duplicate those conditions - you see remarkable behaviors in growth habit. Without CO2 supplement - higher temps are trouble for various reasons and not helpful.

One of the things I've done with my handheld CO2 meter is understand what the various ambient levels are. Outdoors - I usually see something less than 400ppm - being closer to the lungs of the world (Pacific Ocean) and out in country seems to be the difference. Indoor ambient levels are always higher.

 

[GT21]

I recently switched a room from sealed to negative pressure and the rh is a steady 50-55% with temps maxing out around 80, but typically around 77. These have done as well as when I was running 83-86 degrees, 70% rh and co2 sealed up. Same strain, medium, ferts.

Edit: so, maybe the negative pressure of the air has an effect on the plants stomata.

It does... because it gives the plant fresh co2 @~400ppm all the time

 

[Ignignokt]

Another observation about the temperature relationship to terpenes - I think I alluded to somehow 'evaporating' terpenes with higher temps. After finding the critical temperatures for the various compounds - I think its clear that if the specific terpene is not there later in the process, it probably never was present. It takes much higher temperatures than we ever discuss for growing to degrade these compounds. As we get cheaper testing, perhaps we can compare that way. Otherwise I think it becomes more subjective with little opportunity to share meaningful notes (sample each other's work)