Optium Conditions for Indoor Growing

[Oldmac]

Hey Spurr,

Thanks for posting so much information, it took me a day to read thru it twice, some parts three times. Then digest it.

I think you missed the entire point of this thread, I was trying to take a scientific research paper and try to break it down to "plabeian" english so that the average grower may gain some usefull information from it. I've been growing cannabis in one form or another for over seventy years now. The last 20+ years getting serious about indoor growing and it was not untill a few years ago that I could tell the difference between a micro mole and a gopher. Having just a few college courses on horticulture a few years back, I tried to learn as much as possible in order to grow the best meds possible in the most economic fashion possible now exclusively indoors.

I ducked the PPFD part a bit, because like I admitted the only person I knew who could take various light sources, and thier spectrums and convert them into photon flux of micro-mole/sec was KNNA. And I agree with you that is were it should end, and not get caught up in "per meter squared". But from what I read you don't differ much from me in certain respects and I likewise would differ slightly with some of your points. But they are pretty minor.

I also realized that you are a master at cut & paste, where I am barely computer literate. Rather then bury people with needless bullshit, I'd rather try to apply the knowledge (and wisdom) to real world growing.

I only wish that many years ago someone would have come forth with good, solid scientific research and explained it to me. That's what I was attempting to do here. Plus it just might spur some people on to do the same.

OM

 

[spurr]

Hey Spurr,

Thanks for posting so much information, it took me a day to read thru it twice, some parts three times. Then digest it.

I think you missed the entire point of this thread, I was trying to take a scientific research paper and try to break it down to "plabeian" english so that the average grower may gain some usefull information from it.

Likewise, for myself. I did explain the hows and whys though, because I for one prefer reading them when I am learning about something, and you seemed to be up on the topic, so I figured you would appreciate the extra info, instead of: "just use XYZ because so-and-so said so.".

IMO it's better to explain the nuts and bolts, so if someone wants to challenge or question a claim the claim-maker can point to the reasons quickly. Then if claim-maker is incorrect s/he can easily fix the spot of misunderstanding. But I know this isn't the thread topic, so I'll shut up about that.

I appreciate your effort to break the paper down into useful bite sized pieces, that is my goal too. However, some of your interpretation of the material was incorrect or off (ex. PPFD of 1,500 all day), so I wanted to help in that regard too.

The paper left out the variable of VPD, which is important esp. with respect to the studies being conducted. Granted, it's easy to find an approximate VPD from air temp and RH temp, guessing on leaf temp, but it would have been better if the paper listed VPD. Another big missing piece of info is the effect of X, Y and Z irradiance levels on Pn, throughout the day, and as total Pn (Pnnet). Without seeing how Pn progresses over the day it's hard to say with confidence what the PPFD should be, for A, B or C hours of light per day (re DLI). The issue of DLI is why providing 1,500 PPFD all day, for say 18 hours, would not be ideal; it could (and probably is) detrimental in some way. But that's fine, because I doubt anyone provides 1,500 umol/plant-canopy-area^2/second.

I have read at least three other studies/reports on cannabis, irradiance and Pn; and all found ~1,500 PPFD (really as umol/~2"^2/second) provided highest Pn for cannabis. That is good news that they all found similar results, and were independent from each other, IIRC.

I ducked the PPFD part a bit, because like I admitted the only person I knew who could take various light sources, and thier spectrums and convert them into photon flux of micro-mole/sec was KNNA.

You can do it too, I have done so. It's easy and free if you use KNNA's spreadsheet(s). All you do is 'digitize' your SPD and count pixel per wavelength upwards from X axis on SPD. Record all data points and input that data into KNNA's spreadsheet. This is all from memory so I might be missing a step or two. Then the spreadsheet offers all kinds of conversions, ex., with two different action spectrum of photosynthesis (ASP) and a sheet for quantum yield (the more accurate version of ASP), as well as conversion into PPFD (IIRC). And you can use the same spreadsheet to input Lux data, IIRC, along with the digitized SPD, and his spreadsheet will give you PPFD (as converted from Lux using the digitizied SPD).

The problem is getting a SPD that is high quality enough that digitization and zooming won't degrade it so far it's not very useful. It's best to use raw data from spectroradiometer. You can contact your lamp maker and ask for the data, not the pretty SPD. Sometimes they will give you the raw data and then using KNNA's spreadsheet is a great way to go. ... or you can do the math by hand, but using KNNA's spreadsheet is much easier and faster.

The trick is you can't measure the actual irradiance at various places on canopy without a quantum sensor; for a high degree of accuracy. Even if you used a good Lux meter and used KNNA's spreadsheet to convert it into PPFD (with the lamp's SPD); the answer will not be very accurate.

And I agree with you that is were it should end, and not get caught up in "per meter squared". But from what I read you don't differ much from me in certain respects and I likewise would differ slightly with some of your points. But they are pretty minor.

Yup, measuring irradiance is important, but reporting it by the label "PPFD" is not important; although it's very uncommon not to do so. As long as the area (squared) is defined it's good.

I also realized that you are a master at cut & paste, where I am barely computer literate.

Ouch, lookout!

I am not a "master of cut and paste", but some have tried to dub me with that title. Usually they dislike me they were proven wrong about something with solid reasoning and sound science, backed up with real-world use on cannabis.

I have not cut and pasted one thing in this thread that is not my own, original, writing and thoughts; with references. The only time I cut and paste anything is maybe an abstract from a study, or an excerpt from a study, or in quoting someone.

Rather then bury people with needless bullshit, I'd rather try to apply the knowledge (and wisdom) to real world growing.

You may see what I wrote as "bullshit", but I can assure you others do not. And if you do see it as "bullshit" you are missing out, a lot, just by shutting the door, as you are.

FWIW, I too apply knowledge to (and gain wisdom from) real world growing. Why on earth would I study and learn so much about this topics with respect to cannabis, if I didn't and don't apply what I write?

I only wish that many years ago someone would have come forth with good, solid scientific research and explained it to me. That's what I was attempting to do here. Plus it just might spur some people on to do the same.

Well, all this info was available to you, but if you didn't have easy access to academic journals (either online or bound), it would be very hard to come by. Even today, with much sound science at our fingertips, people persist in the old ways of hearsay, anecdotal evidence and assumption; as well as whatever the hydro companies write on a bottle

 

[Oldmac]

Spurr, we do seem to have a common pet peeve, the spreading of misinformation based on old myths, unsubstantiated postings and my favorite "my hydro guy". Like I said a few years (actually 5yrs) ago attending a local community college course (adult ed deal + senior discount) on horti but the prof was from Rutgers, agi dept and was really great. That led to taking another couple of classes and opened up to me all these neat white papers.

I have a simple light meter, tho was going to get a quantum meter but none seemed to to be weighted toward LEDs, which I love. Plus now looking at plasma and hybred to LEDs I think that might be the future. Since I found this paper and almost all of them use leaf surface temps I bought an inexpensive (abt $50) infrared thermometer that is more acuarte then measuring temps at the canopy.

Probably a poor choice of words saying it was "bullshit", I didn't mean to make it sound the info was no good (it was) but the shear volume was overwhelming. I would like to ask you if you could post KNNA's spread sheet and any other info you have from him. It is stuck in my old computer along some great tech papers and hope some day to network them together to gain access to them, but it's a PIA. I from an era when the console TV died you bought a table top TV and placed it on top of the old one.....I have a 3 tower stack of PCs, working one on top. LOL

Hope you are not dissapointed I did not want to debate some of the manusha, but I find pissing contests just get everybody wet. I am apprecitive of your info and knowledge and look forward to gaining more knowledge thru you.

OM in late PM

 

[Horsemanrocks]

I have an idea!

I have an idea!

What if we got back to the original intent....OM, carry on.

HMR

 

[spurr]

I have a simple light meter, tho was going to get a quantum meter but none seemed to to be weighted toward LEDs, which I love. Plus now looking at plasma and hybred to LEDs I think that might be the future.

What do you mean "weighted toward LEDs"? A quantum sensor, ideally, will give the same exact weight to all photons within all wavelengths within PAR range. So photons from 440 nm, 570 nm and 670 nm all have the same weight (the same relative 'effect' on Pn). A quantum sensor tries to follow what is known as an "ideal quantum response", which is the same weight from 400 to 700 nm.

There is no quantum sensor just for LED lighting.

Here is an ideal quantum response, and the quantum response of my sensor (the best you can get for under a few thousand dollars):

Quantum Reponse (of Li-cor LI-190 and LI-191; against ideal quantum response):

You can notice how the irradiance is slightly weighted lower in blue (ex., >80%), higher in green and higher in red (ex., > 100%);as well as counting photons slightly outside of PAR range (ex., 390 nm and 710 nm). Those points are not intentional by Li-cor, they are uncorrectable unless the quantum sensor was to cost a lot more. However, the 'flaws' in the sensor actually are kind of good, because they wight photons, at least a little, along a similar path as the K.McCree Action Spectrum of Photosynthesis and Quantum Yield (the latter being the better/more accurate one to use).

There are meters you can use that try to follow a generalized quantum yield curve, basically a straight line starting lower in blue and ending higher in red. But they are not very accurate unless they are very expensive; adding so many filters to get the goal quantum response isn't cheap.

Here is a great report on these topics, I have chatted with the guy who wrote it, a plant physiologist for Li-cor a couple of times, he's very smart and very on top of his game. The report discusses K.McCree and his work, and the difference between various way to quantify effect of photons on the plant (ex., absorption/reflectance/transmittance vs Pn and ASP vs QY):

"Comparison of Quantum Sensors with Different Spectral Sensitivities"
http://www.licor.com/env/pdf/light/TechNote126.pdf
​

Below are various plant response curves to PAR range light, using the last one, the "relative quantum response" (i.e., Quantum Yield), is the best option. FWIW, I plan to make Quantum Yield graphs for cannabis at various life stages, hopefully in the not-to-distant future; but for now what is below is sufficient:

Here is another way to look at weighting of photons in PAR range, below is the APD (from K.McCree) set against an ideal quantum response from a quantum sensor:

Anyway, if you buy a quantum sensor you can simply plug in that data into KNNA's spreadsheet, along with the SPD and I think KNNA's spreadsheet will convert that to weighted version using K.McCree's ASP and QY, as well as K.Inada's ASP.

If you want it, I can post the weights per waveleths for UV-bbe (UV-b biologically effective) radiation, as well as UV-abe. I have the plant action spectrum from ~280 - 330 nm and ~280 - 400 nm. That is very valuable info, with it you can weight the UV irradiance found with a UV meter light one from SolarMeter; if you have the UV-b lamp SPD and KNNA's spreadsheet.

I would suggest you buy a Li-cor LI-190SA quantum sensor and either a Li-cor light meter (LI-250) or datalogger (LI-1400 or LI-1000), then you can measure umol/area^2/second. That is what I do, and it's very, very useful; one of the best tools I have ever bought.

You may also want to consider a UV-b meter, considering you use UV-b. KNNA and I have conversed about this topic a good deal; where it was found ~ 13 kJ/m^2/day of UV-bbe increased THC greatly, and ~6 kJ/m^2/day was also a good goal. I wrote all about these topics in a UV-b thread, about how much irradiance (as uW/cm^2) to provide for X hours to reach ~13 uvb-be. The problem with using a UV-b meter (such as the SolarMeter 6.2) is the irradiance isn't weighted, but the weighting for UV-bbe is drastic, ex., the 'effect' of the photons drops off pretty fast > 320 nm. You can buy a good UV-b meter, that is weighted for the human "... Diffey Erythemal Action Spectrum (EAS) effective irradiance (Eeff) ..." which just so happens to follow UV-bbe action spectrum closely enough in the important wavelength ranges, that we can use the EAS as a 'close-enough' proxy for UV-bbe. And the great news the SolarMeter we can use, either model 6.4 or 6.5; the latter might be the better option and it's less costly, but some math is required to make the measurement useful. Here are the Solarmeters (range from ~$200-240): http://www.solarmeter.com/

EAS from the Solarmeter 6.4 and 6.5:

I would like to ask you if you could post KNNA's spread sheet and any other info you have from him.

Here ya go, KNNA is right about nearly everything he wrote in that spreadsheet, but in some things I do differ with him. nothing major enough to worry about, though, mostly nomenclature and explanation. I also have the info KNNA used to make his spreadsheet, from where he learned how to use SPD with irradiance to find all kinds of useful conversions; I will post those links later.

"Bulb Analyzer Tool (actualized)"
http://www.gardenscure.com/420/lighting/117933-bulb-analyzer-tool-actualized.html

"Bulbs Comparison Tool"
http://www.gardenscure.com/420/lighting/89513-bulbs-comparison-tool.html

​

Hope you are not dissapointed I did not want to debate some of the manusha, but I find pissing contests just get everybody wet. I am apprecitive of your info and knowledge and look forward to gaining more knowledge thru you.

Not at all; much (most/all?) of what I wrote doesn't need to be debated. I do not find that debates always, or need to, turn into pissing contests. IME that only happens when one or all parties let their ego type for them ...

 

[zen_trikester]

Spurr, we do seem to have a common pet peeve, the spreading of misinformation based on old myths, unsubstantiated postings and my favorite "my hydro guy". Like I said a few years (actually 5yrs) ago attending a local community college course (adult ed deal + senior discount) on horti but the prof was from Rutgers, agi dept and was really great. That led to taking another couple of classes and opened up to me all these neat white papers.

I have a simple light meter, tho was going to get a quantum meter but none seemed to to be weighted toward LEDs, which I love. Plus now looking at plasma and hybred to LEDs I think that might be the future. Since I found this paper and almost all of them use leaf surface temps I bought an inexpensive (abt $50) infrared thermometer that is more acuarte then measuring temps at the canopy.

Probably a poor choice of words saying it was "bullshit", I didn't mean to make it sound the info was no good (it was) but the shear volume was overwhelming. I would like to ask you if you could post KNNA's spread sheet and any other info you have from him. It is stuck in my old computer along some great tech papers and hope some day to network them together to gain access to them, but it's a PIA. I from an era when the console TV died you bought a table top TV and placed it on top of the old one.....I have a 3 tower stack of PCs, working one on top. LOL

Hope you are not dissapointed I did not want to debate some of the manusha, but I find pissing contests just get everybody wet. I am apprecitive of your info and knowledge and look forward to gaining more knowledge thru you.

OM in late PM

In this same spirit guys. I don't know about anyone else who has an IR thermo (I do), but there is usually a 10 deg difference between my ambient (shaded under white cardboard, at canopy height, and out of the path of the intake), and my IR readings. So your revalation of higher ideal temps isn't really anything more than a different way to measure FME.

At the end of my cycle this morning (I run 10 pm to 10 am to help with summer heat issues) I was at 73 deg ambient in the cabinet and leaf surface readings were in the 79-90 range depending on their proximity to the lights. Granted, my cabinet is small and I run multiple cfls inches from my top colas which makes for a different dynamic of light spread than hps, but I doubt my observation of radiant vs ambient would be any different in any working lighting scenario. I think many people don't take proper ambient measurements (shaded, out of intake air, etc) which is part of the problem. I have read many places, pardon me... My hydro guys says , that plants can take a higher level of radient heat than ambient, and I think that is the only point the temperature inferences in your article are proving. I like yourself, feel that IR is the best way to check and control temps. The only acurate way really since it takes away all of the variables IMHO, but that doesn't mean we can compare the two types of readings.

You can call me out if I am wrong about any of this, but based on what you have already said I think we may be on the same page with this one and you didn't feel the need to pound this point home!!! Either way, I think it is important to reiterate that the 86 deg mark you are quoting is specifically for an IR reading and doesn't necessarily translate to any other type of temp readings.

Not trying to be a dick here... hopefully you see that!!!

 

[spurr]

In this same spirit guys. I don't know about anyone else who has an IR thermo (I do), but there is usually a 10 deg difference between my ambient (shaded under white cardboard, at canopy height, and out of the path of the intake), and my IR readings. So your revalation of higher ideal temps isn't really anything more than a different way to measure FME.

At the end of my cycle this morning (I run 10 pm to 10 am to help with summer heat issues) I was at 73 deg ambient in the cabinet and leaf surface readings were in the 79-90 range depending on their proximity to the lights. Granted, my cabinet is small and I run multiple cfls inches from my top colas which makes for a different dynamic of light spread than hps, but I doubt my observation of radiant vs ambient would be any different in any working lighting scenario.

I too test temp in the same manner. However, in most cases (ex., outside, greenhouse, under HID) the leafs will be a few degrees (F) cooler than the ambient (canopy) temp; if the plant is healthy. This has do due with transpiration and its cooling power (as well as evaporative cooling power), air movement, etc.

For my setup, under a 1,000 watt HPS Digilux with 'turbo' mode on the Galaxy select-a-watt, the leafs are about ~72-76'F and the canopy temp is about 75-78'F.

Due to the issue of RH and carbon filter for smell, I have to keep RH below 60-65%. That means to keep Vapor Pressure Deficit (VPD) in the ideal spot, IMO, for flowering (~1.15-1.3 kPa) I have to keep canopy temps at 75-78'F, which keeps leafs temp at ~72-76'F.

AFAIK, once canopy temp exceeds ~85-90'F, the leafs can be warmer than the canopy air, under 'normal' radiant heat conditions under the sun and in a greenhouse. I don't let my room get that hot so I haven't tested.

It seems your grow may have lots of radiant heat, no? I think my grow (and the outdoors/greenhouses) have much lower radiant heat, than might be the case in your garden. If so, that might be why your leaf temps and mine do not agree. Ex., my HID is in an air cooled hood with a water-cooled radiator cap to cool the hot exhaust air. The cooled exhaust air is dumped right back on top of the plants. And there is lots of air movement in my grow.

But I agree that temp isn't the only critical factor; using RH, canopy temp and avg. leaf temp to find Vapor Pressure Deficit (VPD), is more important than either temp or RH alone. Unless either are in extreme ranges. VPD has much impact on plant growth, rate of photosynthesis, 'venting' heat from leafs, etc.

You may want to consider finding the VPD for your room; I can do it for you, if you post the avg. RH at canopy (using a good hygrometer, like analog real-or-synthetic hair and easy to calibrate; NIST certified accuracy and factory calibration is also nice). Every single hydrometer I have tested was far inaccurate, including hydrometer's on expensive tools like the CHHC-4 environmental controller.

Taking VPD into consideration, the ideal canopy temp is indeed below 86'F in that study; probably below 80'F dependent upon RH and leafs temp. IMO that is why in that study, the highest rate of photosynthesis (Pn) at 77'F (25'C) was found at 2,000 PPFD, because when VPD is (close to) ideal the RUE (Radiation Use Efficiency) is high, amongst other area. That means the plant can sometimes have its photosynthetic capabilities increased, ex., the point of light saturation can increase vs in non-ideal VPD conditions.

In the figure below, from the study, it shows at 77'F the highest Pn was found with 2,000 PPFD; that said, the peak Pn at 77'F is lower than the peak Pn at 1,500 PPFD for 86'F (30'C). However, if we look at the angle of trajectory for the Pn line at 77'F (25'C), we see it's climbing, past 2,000 PPFD. So, if the workers (researchers in that study) looked at Pn over 2,000, say 2,200 PPFD at 77'F, it could quite possibly be higher than Pn at 1,500 PPFD at 86'F. In the figure below, we can also see the Pn line at 86'F (30'C), and we see it starts to drop after 1,500 PPFD; unlike the line for Pn at 77'F (25'C):

-------------------

-------------------
​

What that means, IMO, is a bit contradictory, but only because it would be hard to provide ~1,500 umol/area^2/second to each plant in the canopy, let alone >2,000 umol/area^2/second. Even though using a canopy temp of 86'F is best following the figure above in terms of (slightly more) realistic irradiance a grower can provide to each plant (i.e., 1,500 umol/area^2/second), and that the VPD would be out of the ideal range (hence the contraction), few growers (if any) will/can provide 1,500 umol/area^2/second per plant. I for one try to ideal provide VPD and avg. irradiance for each plant of ~1,000 umol/area^2/second (down to 800 umol/area^2/second and up to ~1,200 umol/area^2/second).

What I would like to see is a graph of Pn every 15 or 30 minutes of every hour over the whole daylength. I would like to see testing of 800, 1,000 and 1,500 PPFD at 86'F, as well as 800, 1,000, 1,500, 2,000 and and 2,200 PPFD at 77'F. I think the latter (77'F) with ideal (or near ideal) VPD would have a better long-term rate of photosynthesis as shown on a graph (ex. over 6-8 hours), as well as higher 'daily net rate of photosynthesis' (Pnnet) vs 86'F (not ideal VPD).

I think many people don't take proper ambient measurements (shaded, out of intake air, etc) which is part of the problem. I have read many places, pardon me... My hydro guys says , that plants can take a higher level of radient heat than ambient, and I think that is the only point the temperature inferences in your article are proving.

AFAIK, in the study OldMac posted, the researchers measured ambient air temp around the leaf (i.e., canopy temp), not the leaf temp with an IR gun. AFAIK the leaf was in a clamp/chamber with glass over it, the leaf was in the 'chamber' and had air passing over it at set rate (speed). I am pretty sure the temp listed (ex., 25'C and 30'C) was air temp, not leaf temp, tested as it existed the chamber(?). If so, in the case of that study, the leaf temp should have been about a couple degrees (F) cooler than the listed air temp. So leaf temp was probably ~75-76'F for air temp of 77'F (25'C), considering it was in direct light and had near ideal VPD. The leaf when tested at higher (not ideal) VPD would have been warmer than the leaf at (close to) ideal VPD.

I agree leaf temp is more important than canopy temp, but both are important, and not only for VPD. Neither should be allowed to exceed ~89'F (dept. upon RH in terms of ambient temp) due to the possible issue of hindering/reducing Rubisco activase (the same stuff higher Co2 can hinder, as I wrote about in earlier post).

You can call me out if I am wrong about any of this, but based on what you have already said I think we may be on the same page with this one and you didn't feel the need to pound this point home!!!

Whom are you addressing, me or OldMac?

Either way, I think it is important to reiterate that the 86 deg mark you are quoting is specifically for an IR reading and doesn't necessarily translate to any other type of temp readings.

Ah, okay, I think you're addressing OldMac. Let me ask you, where in that study did you read that the researchers used IR reading of leaf, for the temp listed (ex., 25'C and 30'C)? I have read that paper a few times, and I don't recall reading a description of testing leaf temp. Maybe I missed it, if so, can you please point it out to me? Thanks.

 

[ShroomDr]

No one has a problem with the fact that they used all the same clones? No genetic diversity? I know ive had a few strains/phenos that start to stretch ~85-86F.

From what i take, from what has been posted, ~85-86F is too high anyway, but as i was reading the mode of experimentation, i couldnt help but think my MJ phenos would have performed differently than their mexican sativa.

FWIW, i have no idea the validity of this story, but im 99% sure ive seen a Mel Frank youtube video where Mel talks about the origins of G-13. Again my memory is fuzzy (one guess), but im pretty sure he said the Univ Miss program was a joke, they were doing everything wrong, their genetics sucked, etc. G13 is supposedly an afgani, not a mexican sativa, so i guess its irrelevant to this study, but it makes me wonder why they didnt use more than one genetic representative. (<- a possible example of a 'joke of a program')

 

[spurr]

@ ShroomDr,

I agree, and besides, temp should be a range, because it's never static for long. I have read three other papers/reports on PPFD and highest rate of photosynthesis for cannabis, and I think at least one of the them came to similar temp findings as this study. And the other studies used different race/varieties or cultivars, and even species if you are in the 'indica' is a different species than 'sativa' camp

I will post those studies/papers here, shortly.


@ Oldmac and Zen_t,

Below is a quote from the study, where temperature control/measurement is discussed. From the below I assume the temp listed (ex., 25'C and 30'C) was not leaf temp found with an IR thermometer gun; but with a thermometer in the housing described below. I could be wrong, and if you know where it shows temp of leaf was used, please point me to the section, thanks!

Temperature of the cuvette was controlled by the integrated Peltier coolers, which is controlled by the microprocessor. Different concentrations of CO2 were supplied to the cuvette of climatic unit (LI-6400-01, LI-COR Inc., USA) by mixing pure CO2 with CO2 free air and were measured by infrared gas analyzer. All the measurements for gas and water vapour exchange were first recorded at lowest PPFD and temperature condition and then subsequently to the increasing levels of these parameters. Similarly, leaves under optimum PPFD and temperature conditions were first exposed to the lowest level of CO2 concentration followed by elevated levels. Air flow rate (500 mmol/s^-1) and relative humidity (55 ± 5%) were kept nearly constant throughout the experiment. Since steady state photosynthesis is reached within 30–45 min, the leaves were kept for about 45–60 min under each set of light conditions before the observations were recorded.

 

[zen_trikester]

OK Spur. Understand that I have no intention of wrapping my head around this whole discussion. It is interesting enough for me to read through obviously, but n/a for my system because I am small scale (less than 2 sq.') and my climate control is an exhaust fan and whether I do heat, a/c or open windows in my home. Exact temperature control is something I don't even aspire to with this system. When reading this, I simply put on the breaks when I pictured people running 85f ambient w/o additional co2 and putting a hurtin on their plants. I'm not going to say I have top of the line testing equipment, but it is at least consistent with other similar devices in my home and if I get into the mid 80's my babies won't last long, although I find that mid 80's for radiant is ideal and especially in the summer months when my humidity is higher. This preference is of course anecdotal and based soley on my personal experiences.

First point to note is that I assumed that it was radient readings in the article based on what Oldmac said. I read through the Material and methods section and since this was not mentioned at all, I am going to question scientific procedure used by the author(s). It is bunk without knowing how the temps were measured since (I think) we can all agree there are many variables for any method other than radiant leaf temps.

Is my system higher on radiant heat than yours? Absolutely not! It is far lower if you are running HPS regardless of your kick ass hood. I just have my plants closer to the lights than you do. If you can maintain a 90deg f radiant leaf temp at 1" from your hood then we are the same, but I don't think that is possible! We aren't running even similar systems, but either way if you move your plants closer to the light you get higher radiant heat right? So, based on how my system works, you are wasting a ton of light by keeping your plants so far from your lights as to maintain a radiant temp in the 70's. In my world you could safely increase the amount of light your plants absorb and still be within a working/ideal temp range. Of course the rest of this article may certainly counter that theory, but like I said I'm not wrapping my head around that!!! I don't know if that would translate to more or better bud in your system... you obviously are way more into the science of this than I am, so I truly doubt any suggestion I could make would put more bud in your jars. We just need to keep in mind that we are 2 different worlds for our lighting... I am pushing for maximum penetration where you are going out of your way to minimize temps. We all need both, but I'm sure you can see my point.

The point I originally wanted to stress however, was the opposite of that. I would hate to see someone who had similar ambient to radiant ratio as myself (which I assume to be more typical than what you maintain) and then try to maintain an ambient of 85f which fme, is a good way to stunt growth or flat out kill plants. I'm sure there are plenty of people who are getting far higher radiant temps with cooled hoods and hps just by moving their plants a few inches closer to the lights than you do... ie it isn't just a micro/floro thing! I will be interested to know if Oldmac does ambient readings as well and the experiences of anyone who does both types of readins.

Thanks for the discussion

 

[ShroomDr]

So can someone put this in one or two sentences? I'll try, please correct me where i stray.


77-80F, and 1000ppm CO2 are the sweet spots (was rH mentioned?). You can go higher on the temps, but the higher you go, the more the stomata close, negating the effectiveness of a 1500ppm CO2 level. Also studies show C3 plants are best @ ~1000ppm, there are no MJ studies supporting 1500ppms.


And what im inferring is that if you cant get your temps below 85-90F, 1500ppm is still advisable... is that correct?
(Obviously if C3 plants have evolved @ ~1000ppm, a little higher ppm might help slightly more, and perhaps this slight bonus negates the slight ill effects of the helplessly higher temps. <--Just shooting the shit with this one.)

 

[Oldmac]

@ Horsemanrocks, really glad to see you around, not sure how much more class there is going to be on this thread.

@ Zen_tikester, you are definately NOT being a dick, you raise a valid question. I have found that under HPS, and to a lesser extent PSMH that surface leaf temps at the top of the canopy to be higher then ambient. With a TI ProBloom LED light just the opposite, lower leaf surface temps then ambient. I too contribute this to radient heat generated by HPS and PSMH.

@ShroomDR, I think you are off the mark with co2/temp. Maybe spurr can put it in simple terms for you to understand I need to vape my brain straight with all the munucha that's been posted.

@who ever asked abt methodology; this research used a LI-COR, LI-6400 grow chamber for measurements. It is a "leaf clamp" device so ambient temps are abt the same as leaf surface. And yes they used a mex sativa and only that. Virtually everything we grow is a sativa/indica hybred, they do not appear in nature, they are man made. The difference is sativa doms prefer less day/night differential then indica doms that prefer more. 5 degrees the first, 10 degrees the second. This is a real world starting point....your mileage may vary. There is a bigger difference in RH tolerance.

I wanted to get into relative humidity, that was not covered in this study, but I have to go medicate. Thanks all.

OM

 

[BlueGrassToker]

I am a simple man and try not to complicate things too much. However I do enjoy researching things a bit so I at least have a guide that helps me towards optimum.

I fixed up a small armoire cab a few years ago and decided to incorporate an air conditioner into it. I am talking about ~2ftx2ft footprint chamber x 5ft tall. The main reason for the air conditioner is that the cab exists in a non-climate controlled garage and summer temps can reach a bit over outdoor ambient. Living in the mid-south this can be a bad thing for the summer grows.

I have no data base or documentation for that matter, but I have come to a conclusion that I would like to hear you guys weigh in on.
It involves the root zone temperatures.

My AC is all the way on the floor. And as cold air sinks, the majority of the coldest air stays circulating at the lower parts of the cab at the root zones. I have found that if I keep the root zone (or the ambient temps surrounding the grow bags...as I do not have a handheld IR reader) at approx 67-69F then the ambient temps at the canopy stay at about 80-85F. I have found that I produce the best harvests in this situation.

Now, during some parts of the year in an attempt to decrease the electric bill, as well as trying to save myself from excessive bitching from my better half, I will discontinue the use of the AC. When the ambient temps in the garage are right, I can grow with about the same ambient canopy temps (80-85F) by just letting the air exchange fan do the work. However, the root zone ambient temp will be within 2-5F of the canopy temps.
In this situation it is clear to me that the yield is less, and although it is probably just my imagination, it seems the quality of the bud is a bit less than when I am growing with the AC on.

I hear talk about optimum temps, but never hear too much about any differentiating between root zone and canopy temps.
See, most indoor growers are going to see root temps slightly below canopy temps. But in nature this just isn't happening. The plants are rooted in a near constant temp environment.
There has to be some sort of relationship that suggests a formal study needs to be done, if it has not been already.

Soil temps have to come into play. I have not seen much talk about the relationship between canopy ambient and root zone ambient (soil temps).
I know for a fact that studies have been done in this area concerning other crops such as corn and soybeans.

 

[Oldmac]

Hello BlueGrassToker,

I have found that if I keep the root zone (or the ambient temps surrounding the grow bags...as I do not have a handheld IR reader) at approx 67-69F then the ambient temps at the canopy stay at about 80-85F. I have found that I produce the best harvests in this situation.
You have found both the sweet spot for canopy temp 80-85F and root temps that I've seen as best...roots abt 15 degrees cooler. In my personal grow in RW they are never quite that much lower maybe 5 degrees less, but I have no control over it. But in aero/fog trays in a partnered grow where we have more control, that 15 or so degree less root zone works best for us.

But in nature this just isn't happening. The plants are rooted in a near constant temp environment.
Outdoors by me with a 90 degree day plant leaf temps run in that 80-85F temp area, breeze and air exchange of leafs probably account for that. But ground temp is lower sarting just under the surface. Dig down and it's cooler. That's why dogs and other animals will excavate a small depression to lay down in....it's cooler.

I know for a fact that studies have been done in this area concerning other crops such as corn and soybeans.
I have a study of soybeans (stuck in my old computer) that showed increases in photosynthesis and water utilization when root zone temps are cooler then canopy temps. I don't recall now how much of an improvement or what was found to be optium tho. But confirms what you are seeing.

OM

 

[zen_trikester]

BGT I have found the opposite to be true. My production in my cabinet is lower in the winter. My lights-on ambient temps are only a few degrees lower than other times of the year, but root zone temps are in the 60's. About December of last year I put a seedling mat in my flower cabinet and left in on 24/7 until a week or so ago. This actually raised my ambient temp a couple of degrees since my cab is so tiny, but more importantly it got my root zone into a comfortable range that increased overall vigor exponentially. My moms are all definitely more sativa leaning or straight up hybrids. Working on some indi doms now. Maybe Oldmac's points above are relevant to our different experiences. My humidity levels are super low in the winter also so heating my soil may increase evaporation and help things that way also. Since my hands are pretty tied in terms of adjusting humidity inside the cabinet I don't monitor it regularly.

Oldmac, thanks for the comments. It was also I who questioned the methods in the paper. I had no idea what the LI-COR was nor did I know that it's use requires a specific and consistent method for temperature readings. Thanks for the translation.

 

[Oldmac]

No problem Zen_trikester,

As to the root zone temp, it is much like ambient air temp, too much and it hurts plant growth, too low does the same thing. A root zone in the 60'sF is just too low, as you saw.

Anytime I've refered to a 10-15F less, that's from my optimum of 80-85F at leaf surface or canopy temp.

OM

 

[zen_trikester]

Oldmac, I still don't have my head wrapped around the difference in ambient vs leaf surface readings. I don't take either yourself or spurr as either idiots or bs'rs, so I'm going to do some experimentation on my own. I'm going to move some things around in my flower cab and mess with my fan speeds, turn the seedling mat on and off, move my temp sensor around, etc to see if I can better understand how ambient and surface temps interact. In my case, as is, if I pumped my ambient readings up to 85f I I believe I would be 95+ at the surface and would toast my plants.

My only reason for really commenting here was the fear that some nube would see you guys saying 85 is the new 75 and burn their shit up with extremely high leaf surface temps.

 

[CoRue1013]

anyone ever heard of co2 poising the roots if levels are to high? I am only running about 1300ppm but getting early yellowing of the leaves right aroung 30 days. Looks as though they are in need of nitrogen. 17 years of experience. The only big change I have made is adding Sentential CHHC-2 and running optimal co2. I have had this problem time and time again. i have tried adding nitrogen, changing nut companys, RO water, got rid of fungus gnats, and changed medium. Recently stopped running the co2 and the issue seems better but its early to tell yet. Any ideas?

 

[Oldmac]

Hello CoRue1013,

In the study I tried to translate, they only tested up to 750ppm of co2 because they sighted a previous scientific study that showed that a doubling of ambient co2 level (abt 350ppm) to 700ppm added abt 40% growth. That study also showed that doubling that again to 1400ppm only added abt 10-15% more and they deemed it wastefull. Plus they found water utilization decreased. This was also assuming optium temps.

This study showed the major peak benifit at 750ppm tho I use 800ppm as max in my grows and 700ppm as the low. Trying to stay in that range.

I do have a theroy for you and it involves the roots. The very fine roots that grow just below ground level are refered to as "air roots" and have long held that they do utilize air, and at least one study I've seen suggests that they can use "some" co2. It may be possible that over loading the air roots with co2 could cause some form of root overload. Just my theroy at this point, based on what I've read.

Why not try lowering your co2 use to 750-800ppm and see what haappens? You made no mention where your temps are.

OM

 

[Oldmac]

Oldmac, I still don't have my head wrapped around the difference in ambient vs leaf surface readings. I don't take either yourself or spurr as either idiots or bs'rs, so I'm going to do some experimentation on my own. I'm going to move some things around in my flower cab and mess with my fan speeds, turn the seedling mat on and off, move my temp sensor around, etc to see if I can better understand how ambient and surface temps interact. In my case, as is, if I pumped my ambient readings up to 85f I I believe I would be 95+ at the surface and would toast my plants.

My only reason for really commenting here was the fear that some nube would see you guys saying 85 is the new 75 and burn their shit up with extremely high leaf surface temps.

My feeling and what I try to tell people, if you don't have the ability to read leaf surface temps, go by a temp reading taken as close the leaf canopy as possible. This air reading temp should reflect the radiant heat effect of HID lights, and with luck should be slightly more then leaf surface....unless you got a HID light real close to the canopy. Some of this calls for what people call trial and error or as I prefer....trial and adjustment!

OM