Is VPD important?

[TorturedSoul]

Also on the type of lights he's running. I think the VPD charts are designed for HPS lighting & not so much for LED's.
If you were to look at my 2 current grows you would see I dialed everything in at 77F & 65% RH in one of the journals. Plants grew at a snails pace.

Yeah, warm temperatures are your friend - assuming you have decent lighting. I remember when the CFL bulb craze hit the newbies, years ago, people seemed to start aiming for noticeably cooler garden temperature targets. I was still using HIDs (albeit lower wattage ones and less of them, because I had quit selling before that point in time), and couldn't understand why they were worrying about mid/upper 80s, lol. Oh, yeah - less light and less intense light. We all know that there is a relationship between amount of light, temperature, and CO₂ level. But temperature is not just relevant for those who add supplemental CO₂. The amount of light-energy cannabis plants are capable of processing vs. temperature curve starts way before the point at which additional CO₂ becomes a requirement in order to make use of more light.

Might be a good argument for having (more?) IR diodes in LED grow light panels. Sunlight contains a bunch of infrared (52 to 55 percent). High intensity discharge (HPS and MH) bulbs have a good bit in their spectrum, and LED grow light panels typically produce... some .

A guy named Bruce Bugbee is the president of Apogee Instruments, the company that produces the excellent PAR light meters/sensors. But Dr. Bugbee also has a PhD in botany - and Director of the Crop Physiology Laboratory at Utah State University in their Plants, Soils & Climate Department. He has also been named a Fellow of the American Society of Agronomy, and has authored (and co-authored) a number of scientific papers in the field. Pretty learned guy with lots of knowledge and experience; he has studied recirculating hydroponics for ~40 years, began working with NASA in 1981 (he was part of the team that grew the first plants on the International Space Station (although I do not think he was one of the "hands-on" people who were in orbit, lol), was involved in the creation of the Space Technology Research Institute Center for the Utilization of Biological Engineering in Space, et cetera. He has also produced some video lectures which have been uploaded to YouTube. They're pretty interesting (I thought so, at least), and he's sort of a character... They're probably worth viewing. Oh, and he is a friend of cannabis . Anyone searching YouTube for Dr. Bruce Bugbee will immediately figure that out upon seeing video titles such as "Maximizing Cannabis Yields with Dr Bruce Bugbee."

If I am remembering correctly (flip a coin), the one titled "Cannabis Grow Lighting Myths and FAQs with Dr. Bruce Bugbee" might be useful. Well, several of his are probably useful - but that could be a good one to start with.

 

[nivek]

i have seen the charts and like the pretty colours and shapes. Worth checking out for that alone

My impossibly low humidity where i live make it pointless to concern myself about vpd

And why would i be concerned? I grow fine weed indeed

Karma sent friend

 

[bluter]

Plants grow off the 9 cardinal points. Balance. Increase light. Increase everything else.

Vpd has to deal with how the plant effectively breaths in its climate and uptakes water and nutrients. That’s 4 cardinals out the 9.

Leaf surface temperatures are the ones that directly affect that plant. Like putting your hand under a hps back in the day. Not ambient. However not to say ambient is not important. It’s very important

The people claiming plants grew faster out the sweet spot. Was because your sweet spot was to cold to begin with. 84-86 seems to be the sweet ambient spot with a lst of 77-80. Under led. I just personally noticed a jump in how many shoots took dominance right away to start early training. Idk. I was told by a buddy of mine. Whom is very reputable in my books. Said imagine using a high elevation mask all the time. That’s how a plant feels outta range. Kinda made me feel bad lmao

mine kinda comes in cooler. when things get in to that 30c range it's a struggle for me under led. that's about where you're beginning.

i noticed my plants did much better under hps with a higher temp 28 - 30c, and under led with a lower temp 24 - 26c. when the lights were par measured side by side, the led put out greater intensity. it's frankly opposite to what i've read is the considered norm.

i have a friend running both a 1000w hps and a 600w led cob rig side by side. he considers them equivalent. he rotates the plants, both lights are in the same flower space, so they share the same temps.

he tells me the plants have a more 'relaxed' time of it under the led ... whatever that means lol ... he says the buds will grow a bit faster under the led, and the fans will reach or pray more in the morning. on the opposite, he feels the trichome development happens better when they are under the 'hot' light. he rotates the plants at feedings, so they get a few days under each. it's anecdotal, but i find it interesting.

 

[bluter]

My impossibly low humidity where i live make it pointless to concern myself about vpd

And why would i be concerned? I grow fine weed indeed

kinda in the same boat. if i chased those charts everything would blow up.

i get that it can work for others though. my approach would be : stick to it if it a) works, and is b) easy. otherwise it is utterly not worth it.

 

[Buds Buddy]

I think VPD is a very useful tool for growing. However I don't think that you can dial it in based on a chart. It's also important to know the leaf temperature as it can be quite different than the ambient temperature, especially with different light sources.

On my first grow I left the humidifier in the tent at 65% based on the charts. After three weeks I couldn't figure out why the plants were struggling. I decided to measure my leaf temperatures and realized that with the LEDs my leaf temperatures were several degrees below my measured ambient. I lowered the RH down to 55% and they took off.

Buds, is it possible that by measuring VPD based on the ambient temperature your missing the sweet spot? If your leaf temperature are a few degrees below your ambient your VPDs could be < 1.0.

I believe there's a sweet spot where temperature and humidity is balanced to allow for optimal plant respiration (ie. perfect VPD). I also believe that sweet spot changes as a plant goes through stages of development. I don't always hit the VPD I am shooting for, but I keep shooting anyways

I kind of think you're right. What I'm saying is those charts say the sweet spot is 77 - 78F with 60% - 70% RH during Veg. & that might be true for HPS because it will provide the higher leaf temp. Now if you go by leaf temp only & not ambient temp the charts may be more accurate. But the charts aren't telling you whether they go by Leaf Temp or Ambient Temp so which RH level are you suppose to be at. The 84F Ambient Temps RH or the 77F Leaf Temps RH ? There should be separate charts for different lighting if they are going by Ambient Temps. Sure wish I was better at explaining stuff, but it's not my strong suit.... lol.

 

[bluter]

the charts aren't telling you whether they go by Leaf Temp or Ambient Temp so which RH level are you suppose to be at.

the plant creates a microclimate at the leaf surface, partly through regulating transpiration. it does raise an interesting question.

 

[Buds Buddy]

The people claiming plants grew faster out the sweet spot. Was because your sweet spot was to cold to begin with. 84-86 seems to be the sweet ambient spot with a lst of 77-80. Under led.

This is exactly what I'm saying. Only the charts don't tell you to go by leaf temp & not the ambient temp so we assume since it has to do with environment that they must mean ambient temp. Therefore, we get things wrong. My first few grows I didn't have an AC or Humidifier so temps & RH were all out of whack. But all my best grows (biggest yields) came from those grows. Then I heard about VPD charts & dialed everything in thinking I was suppose to go by ambient temp & my yields decreased & my 6-8 week veg turned into 11-12 week veg to get the same size plant. So, I'm like wtf ?
This doesn't make sense. So I decided to try a grow not using the AC & things are growing fast & nice like they use to.
The difference in the size of the plants between what I was doing & what I'm doing now is way different in way less time.

 

[Delps8]

hps and led light are very much different. led burn can take the form of a genetic looking malformation. led photons can damage cell structure in developing leaves, in the absence of heat. hps typically creates a heat burn before that happens. both can bleach a plant.

I never grew under HPS. Used a blurple in 2017 and now a Mars SP 3000 and a Growcraft X3. I demonstrated, beyond any doubt, that high light levels can cause fox tailing and I'd put that under the "malformation" heading. No question about that. The pisser was that I was trying to light a 4' tall auto and a 2' tall auto by canting the light. Fortunately, I got my head out of my ass about buying a light for the little guy and ending up with a nice harvest from it. The big plant yielded about 100 linear feet of branches (got the pictures) that had absolutely no nugs.

i wouldn't necessarily recommend that. 18 - 26c is pretty much optimum if you can maintain it. most will cite that range for flower, but it's a good all around temp range.

there is a +/-- of 4c where things will still be ok, but growing or development may be affected. things get super problematic if you start getting outside of that. it's also true they like it a little warmer in veg and a little cooler in flower. which runs counter to how most grow spaces move, but that's what we deal with.

i personally try to maintain it in the 22 - 24c range, but usually wind up a degree or two higher.

Check. I've read tons of recommended temperatures and most are in that range. A big influence on my thinking was the data in Chandra. 25°C and ≈ 800 µmoles got my attention. This data is from a CO2 enriched environment but the curves shown here are very similar to what I've seen in other sources.

you are dead on correct. most don't take leaf temps, and go by ambient room temp. it can also be an issue with led, as led can cause damage in the absence of heat.

My experience has been leaf temp ≠ ambient but my offset values have ranged only from 1 to -4, the latter for just a few days. If you consider that the accuracy of our temperature sensors is ±1°F, at best, not using LST/offset shouldn't have tanked a grow.

When my current grow was in seedling stage, the LST offset was 1 and that concerned me - I didn't make sense that plants should be hotter than the air in the tent. Temp and RH were within recommended ranges so I decided to do nothing. As of this morning, they seem to be doing well.

This month-long view shows both both seedling and ver with VPD of 0.8 as target in seedling and 1.0 in veg. This week view is easier to see the trends. I'd love to have a more consistent temperature but the tent is in an unheated two car garage. When the car comes home, temp goes up by at least a few-very welcome degrees.

Back to the question from the OP -- "Is VPD important?". For me, it's a no-brainer gift. The Pulse was $200 and if VPD is out of range, it will display instructions a la "You relative humidity is 58.4%. Increase your relative humidity to 62.4% to reach your VPD target." So I switch to the Inkbird app and bump the RH by 2%. Thirty seconds and a couple of mouse clicks to get things back inline. That works for me.

 

[The70’s]

My basement (where i will be growing soon) is a steady 68° and 42% Rh….. just saying

My son is coming by for dinner tonight, im going to ask him if he would do some watering, while im away once i start my first grow. Im starting with (4) plants in living soil. I hate to say too much cause it causes the old timers to have brain hemorrhages Lol Why ja buy that, You dont need that, why didnt ya buy this ect….

I have (4) LED panels for a total 420watts is what my meter says. I have a 4x4 and an AC Infinity 4T with the controler, its nice

 

[Skunksta]

100% beleave it works tbh.
Would love to see a side by side.
Clone test to see how much better.
In a controlled environment
Two tents one a steady temp and r/h
One following a vpd chart.
Great debate btw.

 

[The70’s]

Leaf temp is part of the VPD calculations, i picked up a cheap laser thermometer once i thought i would be doing these calculations…….

 

[bluter]

This data is from a CO2 enriched environment but the curves shown here are very similar to what I've seen in other sources.

CO2 changes things. i've always found it to be of even less use than a vpd chart.

My experience has been leaf temp ≠ ambient but my offset values have ranged only from 1 to -4, the latter for just a few days. If you consider that the accuracy of our temperature sensors is ±1°F, at best, not using LST/offset shouldn't have tanked a grow.

i've never found lst to be a factor at all.

When my current grow was in seedling stage, the LST offset was 1 and that concerned me - I didn't make sense that plants should be hotter than the air in the tent.

it makes perfect sense. the micro-climate created by the leaves can be markedly different than the surrounding environment.

Temp and RH were within recommended ranges so I decided to do nothing. As of this morning, they seem to be doing well.

good call.

Thirty seconds and a couple of mouse clicks to get things back inline. That works for me.

i'm not as confident in those systems. i know a guy who changed his parameters from 180km away, then watched his grow and house burn down remotely. the fan seized making the change, then overheated and started the fire. he got to go home to the police and the fire dept.


i always like being present to monitor changes.

Leaf temp is part of the VPD calculations, i picked up a cheap laser thermometer once i thought i would be doing these calculations…….

that's the best way to measure. considering you haven't grown yet, vpd charts are the last thing you need to worry about. it won't mean shit without solid lighting and a good set up.

also ive seen those charts contradict each other. the biggest factor will be the ambient environment you are starting with. the charts change with that.

 

[The70’s]

PH of my soil and water seem important too, would you all agree, and is airating the water necessary ?

I picked up a soil and water tester

 

[Skunksta]

Depends how long your feed/ water been standing.I feel

 

[Sueet]

PH of my soil and water seem important too, would you all agree, and is airating the water necessary ?

I picked up a soil and water tester

Just the water, if you get (or make) good soil, the pH is built in, and then you only need to pH the water/nutes.

(and cheap testers are usually a waste of time too)

 

[bluter]

PH of my soil and water seem important too, would you all agree, and is airating the water necessary ?

depends on your water source and choice of media. you won't need it for conditioning if you're on RO.

I picked up a soil and water tester

the soil probes are useless. it's best to learn how to water proper if choosing a soil media.

The Proper Way To Water A Potted Plant

The Proper Way to Water a Potted Plant Also covered: the importance of pH and why we successively up-pot How to Water Over the last several years I have put a lot of study into this, and I feel that I can now define the proper way to water a potted plant. Keep in mind that this discussion...

www.420magazine.com

 

[The70’s]

Just the water, if you get (or make) good soil, the pH is built in, and then you only need to pH the water/nutes.

(and cheap testers are usually a waste of time too)

I picked up a Bluelab water tester and soil tester. They both were used and in good shape, i calibrated both and they seem to hold their calbration :0)

I know its not easy having patience with new growers, but like my wide eyes back in 1984 asking my recruiter what basic training will be like, he said, “You’ll know soon enough”. I’ll never forget it !

 

[Sueet]

I know its not easy having patience with new growers

That is not how we think around here. Welcome

 

[bluter]

I picked up a Bluelab water tester and soil tester. They both were used and in good shape, i calibrated both and they seem to hold their calbration :0)

pics pls. there's a few different levels. you really won't need a soil tester.

I know its not easy having patience with new growers, but like my wide eyes back in 1984 asking my recruiter what basic training will be like, he said, “You’ll know soon enough”. I’ll never forget it !

don't worry.
it might be a bit exciting for a grow or two, but you'll pick it up no issue. there's piles of folk here to help no matter what style grow you run with. just get the basics down first.

then light. lots and lots of light. start with more than you think you want. but you can work in to that a bit.

 

[The70’s]

With my audio/video hobby there are programs to See on my laptop what the sound looks like using a calibrated microphone , its a helpful tool, my guess these are the same, just tools to rule out issues when they arise :0)