Wow that humidity sounds crazy high -- seems like an invite to mold and bacteria to your bud. I've heard that temps upwards of 90 degree's is okay but you do not want temps or humidity levels too high or the stomata will close on your plant leaves (which is how the plant breathes in CO2 in the first place to utilize the molecule as carbon building blocks).
Irregardless the last 2-3 weeks you do not want high CO2 levels or you reduce your bud mass, so humidity is still an issue.
Never heard of the Vapor Pressure Deficit?
How about the Light Saturation Point in C3 plants?
Do you know the correct lighting requirements that actually limit Co2 ppm values?
How about that just about NO ONE can deliver enough light energy to actually
use 1500 ppm of Co2?
The VPD chart is something that for most indoor plants.. you should at least keep an eye on....Especially for things that are needing a fairly consistent RH..Like say Orchid's.
Now for the most part. I ignore the VPD for growing Cannabis. I like a lower (45%) RH in bloom. I control that very accurately. And your right, I do it to help put off fungal spore germination.
Now when gassing cannabis. YOU MUST FOLLOW the VPD for
actual effective use of increased Co2 levels! This whole thing has to do with how the plant can effectively use that increased gas level.
The relationship between the amount of;
Light energy delivered.
ppm's of Co2 maintained
RH and Temps maintained during lights on
Is absolutely
critical to
effective use by the plant of the available Co2!
Lets cover lighting first
Light needs to be delivered at certain intensity amounts to allow the plant to use the increased Co2 at all.
800 to 1200 ppm is basically the range that we can actually employ and get useful, effective results
This light intensity is increased on a
Bell curve... Generally meaning that small increases of light energy can handle small increases of Co2.
The thing is that once you hit 1K ppm. The increase in lighting energy moves towards the point where your not going to effectively be able to employ the increased Co2.
Even basic 1k HPS lighting, is limited to about 900 - 1100 ppm of of actual Co2 concentration.... To go beyond that and to even be effective in using the available gas concentration,,,,you need to be delivering about 1400 watts of HPS to get to 1300 ppm... Beyond that is
effectively not a viable option in terms of cost effectiveness in the yield increase!
Next in line to effectively use increased Co2??? Temps and RH!
In comes the Vapour-
pressure deficit, or VPD, is the difference (
deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated. ... In ecology, it is the difference between the actual water vapour
pressure and the saturation water vapour
pressure at a particular temperature.
What does VPD have to do with growing?
VPD helps a grower identify healthy air moisture conditions over the full range of
growing temperatures. Vapor pressure deficit correlates directly to plant transpiration rates. ... High
VPD can cause wilting when the root water intake can't keep up with the leaf evaporation loss.
Ok, first I'll point out that we, growing our chosen plant. Hate fungus spores and mold spores growing on our plants.... We have far more Mold problems but, the point being. We do what we can to keep RH down to levels that inhibit mold spores from growing....Generally 50% is the industry standard.....Actual premium Temp and RH levels to grow cannabis....Under 75 F and 65% RH.
Now because we don't really follow that. Our feeding is adjusted to compensate for the lower RH we run at. Commercial fertilizer charting is basically charted for our used RH levels....We further got to the feeding rates we want by dialing in our feeding to our strains and their environment. What I'm saying is that savvy growers know to adjust feeding to their strains for optimal growth. This IS directly effected by the environment....Temps and RH are a part of the enviro.
Below is a VPD growing chart. I employed these constantly in greenhouse operations.
Take a look at where that RH and the 90 F TEMP intersect.... You accepted the temp given above as effective. Yet your RH is too low to actually effectively
use all of your increased Co2.. That is waste and waste costs money!
To effectively utilize a Co2 ppm of 800 or above. Temps of 90 F and an RH of 80% is needed in the grow area!
VPD chart
The easiest way to control your grow room for gassing?
An environmental control unit! This unit will turn on and off the gas at night.
You also set the temp and RH value for the unit to shut off the gas and turn on the exhaust/cooling. This then rides down to a set point you choose and it repeat's the process over and over.....till shut down.
https://4hydroponics.com/autopilot-digital-environmental-controller.html
The Autopilot Digital Environmental Controller (DEC) is designed to control the humidity and temperature levels in your grow room while coordinating the use of supplemental CO2 injection within the temperature function.
It has four (4) receptacles and a remote combination probe with highly accurate temperature, humidity and light sensors.
The 15' remote sensor on the Autopilot DEC is designed to quickly react to changes in the growing area and to resist EMI / EFI from electronic ballasts.
Easy to use push button functions are identified on a large digital display. It has a built-in data logger that records minimum and maximum temperature and humidity levels.
Specifications:
Temperature control range: 41° to 113° F
Temperature accuracy: +/- 2°F
Temperature dead-band (hysteresis): adjustable
Humidity control range: 5% to 95% rH
Humidity accuracy: +/- 3% rH
Humidity dead-band (hysteresis): adjustable
CO2 ON timer setting range: 1 second to 12 hours
CO2 OFF timer setting range: 1 second to 96 hours
Input voltage 120 Volts AC
Maximum amperage: 14.5 amps @ 120 VAC
Weight: 5 lbs
Dimensions 9" tall x 7" wide x 4" deep
NOTE: This APCETHD controller has a 14.5A maximum load. For higher amperage units, such as A/C units, it is recommended to use a power expander.
Covered by a 3-year warranty.
I see somebody mentioned that you MUST turn OFF the gas for last cpl of weeks of bloom.... From past experience, I did it at week 7 (stop gassing) and let them finish out.
High Co2 levels inhibit Ethylene production by the plant. Ethylene gas does the actual ripening of the plant....Same as fruits..
If you do not follow the VPD when using gas.....Your shooting yourself in the foot!
All of this information. Can be verified in Ed Rosenthal's books!
I made it simple and understandable....
I could give you pages of technical answers.....Including why the plant decreases growth by over 30% everyday and that by gassing you can get almost all of that lost growth back...
The thing is.....Cost to return ratio's.... At my size. I have to employ Co2 generator's. They simply do not return enough in the long run to use for the size area's I grow in..
What is gassing good for then? Tent growers.....You can use big 75 lb tanks over the limited 40's and deal direct with the gas company for them. Cheaper and last longer...
Be sure your math is correct for your size area (volume)....
I don't gas anymore. Not worth the cost to yield....
Lastly. NEVER gas in veg...Talk about no cost effectiveness!
