What is the optimal range for temperatures and humidity?
- Thread starter marsormai
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BurntByFire
Active Member
Working in conjunction with temperature, humidity ensures natural plant processes such as transpiration, can take place. Maintain vegetative humidity levels between 60-70% (daytime) / 45-60% (nighttime) and flowering humidity levels between 40-60% (daytime) / 30-40% (nighttime). Easier if you have a controller like the Grozone HT2. That’s what I use.
for temps I would say if using LEDs 80 degrees is good but under HPS I would say 72-75 degrees.
for temps I would say if using LEDs 80 degrees is good but under HPS I would say 72-75 degrees.
What about if using window light?
BurntByFire
Active Member
Honestly I’ve never tried growing with window light so I’m not sure. Assume your window is facing south? If not I wouldn’t recommend it
My Name is Mike
Well-Known Member
You're going to have a tough go if relying on window light.
I have window light pretty consistent though, would do you foresee would be the major hiccupS?
My Name is Mike
Well-Known Member
Inconsistent lighting for sure. Doing an indoor grow, the idea is to mirror ideal outdoor grow conditions (light, wind). Hard to rely on outdoor conditions inside in a window. If it's in a room you use, definitely going to disrupt the light cycle.
Keesje
Well-Known Member
Just look at the VPD and you will be fine with a wide range of temperatures and RH's.
The numbers posted above say nothing if they are not related to ambient temperature, leaf temperature and RV.
75 F and 30% humidity is just a bad advice. If your leaves would be 72, your VPD would be over 1.7.
In what world are those good numbers?
Maybe at the end of your grow to prevent Botrytis. But even then a VPD of 1.4 would be good enough.
The numbers posted above say nothing if they are not related to ambient temperature, leaf temperature and RV.
75 F and 30% humidity is just a bad advice. If your leaves would be 72, your VPD would be over 1.7.
In what world are those good numbers?
Maybe at the end of your grow to prevent Botrytis. But even then a VPD of 1.4 would be good enough.
Tetrahedral
Well-Known Member
I recently checked the transpiration limits of marijuana and it's well above 1.7 so not sure your advice is accurate and might want to look into it properly as those charts are full of shit. Only when the plant is water starved would 1.7 be a problem.
Keesje
Well-Known Member
Please give me the link where it says that a VPD of cannabis of above 1.7 is ok for this plant.
'OK' in the sense that it is near ideal values.
It would be scientific news.
And a link that makes sense, not one of some stoner.
Sure a plant does survive, but you want to try to maintain ideal situations. 1.7 is not ideal.
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ISK
Well-Known Member
I recently completed 4 plants from an indoor sunshine grow..... and to tell the truth there ain't much you can do about the temps and/or humidity unless you have an air conditioner/dehumidifier to control the entire room.
IHMO, unless your temps/humidity are really off, you have little to worry about
Tetrahedral
Well-Known Member
Google hemp data, there's a whole decade of study on transpirational thresholds and water availability. It's upto you to learn yourself.
My Name is Mike
Well-Known Member
Keesje
Well-Known Member
I know how google works.
But I can't find any scientific based paper that says that 1.7 is within the ideal range.
But apparently you did, so I am curious.
I mean this seriously as there are hardly any decent studies on VPD for Cannabis. Most things that you read are of people repeat each what they've read somewhere else.
There are plenty of studies done about other plants, like tomatoes and cucumber, chrysants, but cannabis... nope.
I know a lot about VPD, and see how it is measured in commercial greenhouses where I live.
1.2 is about the max. Most growers aim at staying below 1.0.
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ISK
Well-Known Member
Tetrahedral
Well-Known Member
Your chart says on a hot dry day every marijuana plant dies or suffers badly, rather than I educate you why don't you educate me and explain why this dosent ever happen?
The answer is it can draw enough water but I'll be interested to hear your version.
The upper and lower transpiration thresholds for many plants is a highly studied topic, wheat maize and everything else all well studied for good reason of how much water a crop needs. Can't believe you cant find that subject and spend a few weeks learning it.
Keesje
Well-Known Member
I don't use a chart.
I even think that the charts that you see on many cannabis sites are off.
Too high IMO.
My guess is that they come up with these numbers like 1.4 because with a high VPD you have less chance of PM and Botrytis.
And often they don't even consider leaf temperature.
A plant will not die on the spot when the VPD is 1.7. You are right there.
It will live for a long time if there is plenty of water. But 'living' and 'producing yields' are 2 separate things.
Plants will survive in a really wide range of VPD. You can go to 2.2 or whatever.
But that doesn't make it an ideal VPD.
The VPD has not only to do with the fact if a plant can draw enough water.
Because as you said: When there is plenty of water, the plant will suck it up.
VPD has more to do with the absorption of CO2.
When the VPD is too high, the stomata will close.
And thus less CO2, one the main cornerstones that will give you a good yield.
If you look at studies done on tomatoes and cucumbers, you will read that for these (and most other cultivated plants - which cannabis is) a VPD around 1 is about the higher end.
For example in this study it is stated: According to Hoffman (1979), an increase in VPD from 1 to 1.8 kPa determines the major reduction in plant growth on several crops.
Or in this study:
Optimal VPD values are recommended in the range of 0.3 to 1.0 kPa in different sources. For example, Barker (1990) reports that VPD values between 0.5 and 0.8 kPa are optimal for most greenhouse crops and will prevent yield reduction due to fruit shrinkage and fungal diseases. What is more, VPD values between 0.2 and 1.0 kPa are recommended for both pollination and prevention from fungal diseases (Picken 1984; Prenger and Ling 2007). Iraqi et al. (1995) suggested VPDs of 0.8 kPa as the optimal during day and night hours, and reported that both the photosynthetic rate and yield of tomato fruits increased.
And
In another study on the effects of humidity on 26 different crops (Schwarz et al., 2014), VPD between 0.3 and 1.0 kPa were reported to have minor effect, while values above 1.0 kPa were found to significantly affect plant growth.
So I studied this subject for a long time, because I realized a long time ago it was important.
And also because commercial growers told me so. hahaha.
In all those years I have never come across a number of 1.7 being ideal for a plant. At least not for cannabis or other crops we all know.
So you put your money where your mouth is, please.
You tell me you have read it.
I can't find it. Perhaps I am stupid, but they for sure you are willing to help me.
Please give me a link.
I don't write these things because I like a pissing contest or something. But I really want to learn, and to be educated.
If I am wrong, I am wrong. But just saying I am wrong and not coming up with studies to prove me wrong (like I did in this post) helps no one.
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