The Garden's Cure - View Single Post - Optimum temp/humidity throughout a plants life?

knna · 10-14-2007, 08:53 AM

Last quotes

"> evidence of photosynthetic acclimation to elevated carbon dioxide in soybeans results from greater susceptibility to water stress in plants grown at elevated carbon dioxide

translation, if you raise CO2, plants will be unable to use it if the air or roots are too dry.

"On days with either dry soil or dry air, acclimation was apparent. On days shortly after precipitation events and on humid days there was no evidence of acclimation."

http://www.ars.usda.gov/research/pub..._NO_115=112263
---

thanks to plantbuilders acclimation info, it is clear to me that 40% humidity would be overkill.

Thanks to knna's contributions, I take note of the plants Increased need for humidity, as CO2 levels and temperature levels increase.

But look closely at the max humidity levels the Kpa calculators are producing, the max RH is close to 60%, and many grows struggle with numbers that are Way above that, especially in the dark cycle.

So I conclude, Humidity over 60%, or under 50% is going to reduce the maximum ability of the plant to use CO2, even if they get plenty of light.

I agree with DeltaNugz that 1200ppm CO2 and 85F are good max metabolism parameters. And I agree leaf temperatures are key to the game. And I agree VPD in the .9 range, +-.1 is a good target.

To implement these parameters, I would start by controlling for light distance first. Based on lamp size, I target 24" distance from 1k, 20" from 600w, 18" from 400w as rules of thumb.

With the light at that distance, I would then control for leaf temperature at the hottest point on the plant, of no more than 82F.

Then control for room temperature, starting at 75F, no higher than 85F, knowing it may be necessary to run the room lower than 85F, to achieve a limit of 82F leaf temp.

Room temp is not at all the same as the temperature of the air between the lights and the canopy, so I would most definitely not set the AC to 85F.. I like 75F, cause you wont actually get the top canopy down to that temp, since the lights add heat.. hope that makes sense..

As to humidity, given the ability to dehumidify, I would set max humidity to 60%, as knna's info has focused me on that as the max limit, for any temperature, with lower temps, in the 70's actually benefitting from being closer to 50% humidity.. 40% RH is unnecessary overkill

so now our parameters are

CO2 @ 1200ppm
Max Leaf temp for max photosynthesis, 82F
Humidity maximum 60%, minimum 50%
Room temp max 85 (careful with this one, room temp can be cooler than canopy temp, dont let leaf temp go over 82F)

fwiw, if these parameters are not met exactly, it simply means the plant is not growing as fast as it could, but it can still be awesome

Im learning a Lot, thanks again for focusing us on such practical questions DZ, and thanks for the VPD info knna..

Lucas"

"Glad the VPD info was useful for you. This is the wheel of cultivation: ive learnt a lot from you, and now i can apport something

I agree with Deltanugz, the recomended level of VPD is 0,8-0,95 KPa in veg and early flowering, and raising it (reducing RH) when flower stage go advancing. After the first month in flower, i try to get a 1Kpa level, ive notice it works fine. Probably it cost me some yield, but ive observed that resin production is a lot higher.

Although VPD continue ruling the transpiration rate at night, this rate is far lower that the light transpiration, so i think isnt so important. Better if the VPD range is within the reccomended limits, but i believe it will affect much less the grow rate.

About CO2 at 1200ppm, the RH level to get 0.9-1KPa is over 70%. That is a dangerous level to deal with mold, so a logical conclusion is CO2 enrichment apport little in late flowering stage (2 weeks), because at reasonably RH levels (55%), VPD is outrange, and excess transpiration and probable stomata closure will lead to CO2 unused, without advantages over ambient CO2, or at least over slight CO2 enrichment (500-800ppm)."