Humidity 102: Vapor Pressure Deficit - VPD Chart

Vapor pressure deficit explained in 5-ish minutes. What is VPD? How do you measure VPD in your grow room? What VPD range is good for propagation, vegetative and flowering? How are relative humidity, leaf temperature and air temperature combined into VPD and which units of pressure are used?
VPD Online Calculator: opennlabs.com/vpd/VPD_calculat...
VPD Article: www.just4growers.com/stream/te...

[@meyaniboy]

Shout out to all the heavy fruiting annual farmers!!!!!

[@Just4Growers]

+Solo Herbman Indeed! :)

[@danielmacdougall8651]

Cheers from Australia, a heavy fruiting annual lover, overgrow the world ! 😎

[@fuckusername87]

@@danielmacdougall8651 How goes the growing these days mate, soil or?

[@CC-jy4gr]

@John LOVE ME SOME MELONS!!!

[@fsu3784]

🙌🏻

[@Team-gw5uw]

6 minute video I spent 20+ minutes watching. Very informative with pictures and examples.

[@Just4Growers]

Team 626 Thanks for the feedback amigo.

[@gamercatsz5441]

This channel is like my local hydroponics store, it's all about cannabis, without being about cannabis at all. ;) lol But seriously, best info on youtube, well done Everest!

[@ESSBrew]

What is cannabis?

[@greenlife1015]

cannabis?

[@Khramps]

Cannabis ? What are you talking bout

[@Matias-rn9ff]

I know I'm 2 years late to the party, but I would also like to know what cannabis is.

[@AnnhilateTheNihilist]

Never heard of it

[@jondog9]

Master grower on your resume. Love the quick humor, need to watch twice. Lol. Oh yeah, great info here. Very helpful. Very!

[@jordykingstongrows3639]

love this video. VPD is one of the biggest growing environment factors that get missed out by growers. keep the videos​coming 💯✌

[@Just4Growers]

+Jordy Kingston Thanks Jordy, glad you enjoyed the video. Took a while to put it together so feedback like this is much appreciated!

[@delagdo]

Brill video, thank you so much for this and your calculator 🙏 I have used the calculator previously for years but I've noticed it's disappeared. Looking for it again I found your channel, looking forward to watching more of your well made videos.

[@klonestootrichomes4276]

Thanks man, needed that. Thumbs up 👍

[@jdlitson]

+Everest Fernandez I've been subscribed to your chanel for over a year now, and I honestly don't understand why you don't have at least a million subscribers by now. You are like the Elon Musk of growing. Thanks for all the great videos. Much love brother.

[@Just4Growers]

+jdlitson Thanks first and foremost for subscribing! If I had a million subscribers I think it would freak me out a bit to be honest. Lol. Elon is a very cool cat and many magnitudes wealthier than me but my riches is life, as my blud Nester used to say. Thanks so much for your support. It means a lot that you take the time to message! Have a fantastic day my friend.

[@peterlane9212]

Because people like me finds he talks too fast and is highly irritating Too much ego

[@bohaggin5913]

It's his asshole voice

[@chris432t6]

I agree, no doubt pro level for home growers. Once i discovered the videos could be slowed down a notch it was a much better pace for my slow growin stoner-ass!

[@_sunshine_rainbows]

he talks way too fast. i have to watch at .75

[@torktool]

Mr. Fernandez. I really appreciate your excellent videos and thorough explanation of the processes!! May I suggest that you check your VPD spreadsheet. In the drop down, it shows .5 degree cooler when it should be .5 degree warmer. The results for both have the same numbers which makes me believe it's a typo.

[@ktgerloff]

I am not a grower, but a biology student. This video is the perfect mixture of succinct and informative, I found it very helpful. Thank you!

[@Just4Growers]

Thank you Katie, I’m glad you found it useful. Good luck with your studies.

[@jeangonzalezhidalgo1815]

I'm a grower and I'm also a biology student!!! Lol these videos are awesome for discussing these great tools. Love and cheers from Costa Rica!!

[@Just4Growers]

@@jeangonzalezhidalgo1815 I really appreciate that feedback! :) Thank you and hope you and your garden are doing well.

[@michaelcollier8609]

Thanks Everest i was waiting for this video.it will be a great help...... after i watch it 3 more times.

[@surronzak8154]

4:20 just for 420 LOL well done

[@danj285]

@ Everest Fernandez well played!

[@hughoreilly9526]

Keep up the info love all the information packed in one video is impressive!

[@ramseynubani4362]

Great job with this explanation!

[@GreenGrowSpaces]

And I just posted a vid related to this topic YESTERDAY...damn where was this when I was researching, oh well next time you will just have to read my mind a bit better, and sooner! Keep it coming man

[@iuliandan01]

Whoah! The views on this video do not reward the effort put into it. Good job author! I can see the work behind.

[@Just4Growers]

Thanks Dan. Your feedback is reward enough for me :)

[@hazardsmurf1230]

wow thank you. Now I understand. Going to do a walk though and figure it out now Dank you. Growers Love

[@Just4Growers]

+HazardSmurf 420 coming right back at ya! :)

[@ocgsorchardcitygardensuppl3788]

Great content dude! thanks!!!!

[@Just4Growers]

+OCGS Orchard City Garden Supply Thanks for watching. Play them in-store sometimes if you need to punish staff :)

[@phenosgardenupdate512]

Just added this to my 'Gold Reference' Playlist. Thank you for explaining VPD in such a great manner. The visuals helped a lot as well. This is one concept that is best taken into account overall in my opinion just based on the science not experience, though that will change. Thanks again for all of the great content as well the awesome calculator.

[@jmsfamilyonly]

Good one Everest. I believe in propagation control 💚

[@theprinceofliberia6793]

Thanks man. I've noticed that most videos try to confuse us to make themselves look smart i think and make sure to strictly relate to purely scientific terms😂 instead of actually explaining it in practical terms as you did. Thanks a lot I appreciate it.

[@Just4Growers]

Thanks Pete - a lot of time and effort went into this video - so I am grateful for your message. ✌️

[@DONTSTEPNSNEK507]

Good for you buddy ! Thumbs up

[@syoukhan]

I watched a lot of vids and I got to say it: you're the best, finally I got to understand VPD, and it was thanks to you.

[@Just4Growers]

+Matt Holy Comments like yours make it all worthwhile. Thanks Matt.

[@syoukhan]

I think I've already said it in another comment but maybe it's important for you to know, few of the main reasons why I love your vids are: you manage to say all there is to know in just a few minutes, you go straight to the point, your explanations are very clear, you're FAST, and you're funny :) If you put all those things together it's obvious why your vids are gold! Best of luck with your grows and your channel!

[@Just4Growers]

Thanks Matt! Can't be doing with vids that don't get right into it-I am under no illusions that most folks are watching my videos while on the throne. With that in mind, you've got to get in and out in about four or five minutes max before it's time to wipe (or spray, if you're in Asia.) So-looks like I've truly peaked in life. Lol. Seriously-glad you enjoy the vids and know that there are plenty more to come!

[@syoukhan]

back again. Just refreshing my memory. It's kinda funny but whenever I've got a problem I'm like "hmm, gotta watch some Everest vids". I am sitting on the throne btw, dude you're scary accurate. Lol.

[@raisingjanecannabis4831]

Great information 👍🏾

[@tarquinjanis5918]

Beautiful video man

[@Just4Growers]

Thanks Tarquin. I appreciate that!

[@freetickeys]

You're not just a good teacher; you can be hilarious!

[@vascodawilson]

this was an excellent explanation! Thank you

[@Just4Growers]

Marc Wilson Appreciate the positivity! Glad you found the video useful. ✌️

[@meowmix1569]

So VPD recommendation differ from common humidity recommendations. Is this VPD method superior if one wants to go thru teh hassle?

[@miguelsalazarmob]

Which brand do you recommend for that leaf temperature tester ?? Thanks 🙏🏼

[@tprfk]

thanks for the very high altitude recipe!

[@brunomai3337]

Amazing video

[@daveaufradern6658]

Dude, you simply rock !

[@Just4Growers]

+Dave Müller Awesome, glad you enjoyed the vid - condensed from more than a few years' mmmm'ing and ahhhhh'ing I can assure you! Thanks again for validating my efforts!

[@auditocanarsie7355]

Where can I find the VPD or humidity & CO2 levels for Kumquat trees or citrus trees while fruiting? Is it 40-45% humidity like you said at 5:00 for most flowering plants at 5:00 or is there a more specific humidity range for flowering /fruiting Kumquat trees?

[@growers_choice0076]

great work

[@billthebutcher1821]

Great vid

[@goodtogrow7774]

Glad I'm growing legally! I can't do this math though lol! I'm just trying to figure out what temp and humidity i should be at in early flowering and ended up here more confused than ever lol!!!

[@danielmacdougall8651]

As always, excellent ! Cheers from down under (Australia). A heavy fruiting annual devotee 😳.

[@Just4Growers]

+Daniel Macdougall Awesome Daniel - hope your heavy fruiting annuals are blooming bountifully! :)

[@danielmacdougall8651]

Peace and Love to you and yours Everest.

[@jmof0464]

Hey Everest what is an efficient way to keep both my grow box cool and humid (my humidity is about 30% how Can I make it higher) is small about 1.5 cubic meters I got a fan in it and cfl lights and it still gets over 25 degrees and also how can I make my CO2 level higher with out a tank or a burner

[@sameerambekar6460]

Very useful, I learnt a new thing to control my plants health and growth! Thanks 🙏

[@robertthrem3382]

You're quick you could have dragged it on so this time I had enough brains to screenshot your chart thank you

[@marna1795]

Sorry to bother you loved your video just didn’t understand how did you get leaf temperature 0.6626968882 to 4.5993545385 please help. I tried to do everything but couldn’t figure it out thanks

[@jmcasler1512]

Everest, Is VPD calculated as a single point during the day, single point at night or as a daily running average? Are there acceptable or different ranges between night VPD and day VPD?

[@nowy08031984]

Do I need to worry about my VPD during lights out? My humidity usually drops then, humidifier in sync with lights. Cheers

[@therootandvein]

New viewer here. I grow rare aroids and have just built my greenhouse. I have a smart sensor that checks vpd with the option of doing it without leaf pressure deficiency and that's what I've been going by trying to learn this stuff. Right now my temp is 85, humidity 63 and my vpd is 1.52. The vpd is not good but the temp and humidity seem fine? Any advice? I don't see how it's possible to always check the leaf temps to keep this in check:(

[@cycle03]

who makes those humidity domes you had on top of the potted plants? nice!

[@oscarolivas1806]

yes thanks for the info

[@Darthreloy]

I have a self watering pot with about 10 gallons of water, then potting soil, then planted are some potato vines. I added some Miracle Grow to the water. I am in Phoenix Arizona and it gets hot as hell. My pots are outside so no way to control the temp or humidity. I have the condition you speak of when too much water is brought up and too much calcium blocks nutrients. In the case where you cannot stop high heat and low humidity, can you change the water chemistry to help?? Like maybe high PH distilled water with only certain nutrients? Suggestions would be helpful. Thanks.

[@Pez_Destroyer]

You sir, are amazing!

[@Just4Growers]

Gotta lotta love for this video. Thankful for the help I had in making it.

[@dyelonjoyce7130]

Hey Everest I really love your videos and I literally study them and take notes. I’m really trying understand vpd and not sure if im using the chart you provided correctly. I found that without calculating vpsat or vpair you can just take the air temp of 25 in the example and RH of 50% and come up with the same number 1.23 kPa on the chart. Is it that simple? All I need is air temp and RH then plug it into the chart and BAM I have my VPD? Or do you need to figure out vpsat and vpair and then subtract vpair from vpsat to get an accurate VPD measurement?

[@Just4Growers]

Sorry it took me five years to reply. :) Yes, you can simply use the chart - most videos on YT about VPD tend to reference "the VPD chart" - typically the one I published in "Urban Garden Magazine" back in 2010. However, in an attempt to dig a little deeper and fully explain the mechanics, I thought it would be useful to actually show how those numbers were derived-hence the formula stuff / math excursion. Not necessary to do the math, but I know some folks out there will appreciate understanding what's going on under the hood, so to speak.

[@PowerScissor]

I'm not a willing grower here. Against my will, my vinyl shed grows mold on all my tools, storage items, etc. I've been closely monitoring for the last few weeks all metrics before making changes so I will have actual data to see how my changes effect the numbers. What VPD or RH numbers should I concentrate on to keep mold from growing on my stuff over the wet rainy Winter where I live?

[@HisHerGrow]

great info

[@JebGardener]

But you don't really use those calculations, do you? You just keep it at 76ish with a humidity of 40-60 percent like everyone else right?

[@Just4Growers]

+Jeb Gardener Thanks for your comment. Quick rules of thumb are handy, especially if you are used to growing a particular species. I often refer to the chart, because the calculations are tricky to do in my head ;) Seriously, the best VPD sensor is your skin and, as such, you can feel it out just by walking into a grow room or greenhouse. As for temperature and humidity ranges, it's species dependent of course and there's the stage in the lifecycle to consider too. 40% RH at 76F is a VPD of 1.49 kPa - fine for some plants in mid-flower but not for freshly rooted cuttings or juvenile plants.

[@Orholam5]

Aim for the highest humidity you can give them. 40 is much too low as the VPD calculation will show you. Most tropicals will not do too well long term

[@brett2themax]

VPD helps regulate how much food the plant can process. If your VPD is too high in seedling or cutting stage, you will see problems because the plant is trying to eat more food than the young roots can provide.

[@s3cr3ts3rv1c3]

Thank you so much

[@sparkyarreff1917]

Nice. Thanks!

[@oOKenduOo]

Where can I buy that Infrared Thermometer? I dont really find anything suitable online, only for cooking and stuff but not for plants :D Great vid btw!

[@rafaelcamarena5351]

Everest you’re the man.

[@tebindyehblack6127]

Hello Everest and whoever reads this comment can you please explain how you get the vpsat of 4.5993545385 from 0.6626968882 from The (4.5 number) I can work the rest out and I can workout the first part too (0.66 number) but don't get how you go from the 0.66 to 4.5 someone please help me get my head around this

[@thefarmlife4720]

I've been having trouble with your chart and after going through your example I realized that something is wrong with the F conversion. It doesn't correspond to the C at any rate. 25*C -2* leaf temp should correspond to 77*F - 3-4* leaf. per your example @ 50%RH you get a 1.23 for 25c-2*; however at 77F -3/4 it shows 16.4/14.5 respectively. Even if it were supposed to be read in mbar (which goes against the key) the VPD range would need to include 12.3. (I think mbar = Kpa*10) I hope you find the problem. Trying to read that chart was starting to drive me crazy! I guess it's my fault for trying to use F.

[@Just4Growers]

Hi TFL. Thanks so much for pointing this out. I've made a "quick fix" by combining both C and F scales (and going up in 0.5 C increments) while I try and figure out what was going wrong with the F setting. It's too hot today for my brain to work very well-but at least it's spewing out the right numbers now. Once again, THANK YOU and sorry for any confusion. I've made the code downloadable here: opennlabs.com/vpd/VPD_calculator.php.zip incase a more seasoned computer programmer out there wants to take a look. :)

[@raingo5625]

does this mean specific nutrient element like Ca is consumed at a fixed rate? its just that VPD affects how much is actually used by the plants? could you please enlighten me on this? 😁 Thank you Everest!

[@jmcasler1512]

For everyone's benefit, I made a google spreadsheet that you can copy with Everest's formulas: docs.google.com/spreadsheets/d/1Tbk0GnRsuCdLHf8UEe7v4PIFP1NGsfOdRxqbSqgj9Tw/edit?usp=sharing

[@Just4Growers]

+Jm Casler Awesome spreadsheet skills Jm!

[@vojtator]

Up with you!

[@Just4Growers]

nevim neresim what a dude!

[@vojtator]

Everest Fernandez Stoke me a clipper!

[@syoukhan]

thank you for this

[@Vondrayfilms]

when u divide 172.5 with 260.3 you get 0.6626968882 how did u get this im stuck and really wanna copy this method please help

[@HHJoshHH]

I absolutely love watching your videos Everest! Concise and fun; exactly the way that botany should be! Bravo bro! 💯😇

[@Just4Growers]

Thanks for sharing that Jahshi. It took a surprising amount of effort to make a video this short. I sure appreciate the encouragement to make more. 😉 thanks again amigo.

[@HHJoshHH]

@@Just4Growers well I learned how to calculate (or attempt) to calculate VPD from you!!! And more importantly I learned how to take better care of my garden! I know making and editing videos is truly a pursuit in testing the limits of your sanity, but you are the Lilium inter spinas (the Lilly among thorns). 😉❤️💯🤙🏼

[@tomtreecutter1586]

So if I am at about 6000 ft above sea level where do I want my VPD numbers at?

[@Terranscapes]

Excellent info on something I've not heard mentioned elsewhere. Thanks! But I have a question: When you are measuring the RH and Temp of the room, do you take that reading under the lights or in the shade/away from the lights? In the shade the temp is lower (no radiant heat from the lights) and has a lower humidity. This seems more accurate for the majority of the plant assuming there hasn't been significant pruning below the canopy and represents the rooms actual measurements. But the top of the canopy's RH and Humidity is where the most active growth is occurring. This would seem to support taking measurements there. What do you recommend? Thanks for another great video!

[@Terranscapes]

Hmm... Perhaps with enough circulation the difference becomes negligible?

[@Terranscapes]

oops. I meant in the shade there is a 'higher' humidity.

[@Just4Growers]

+Terranscapes Thanks for the awesome questions Terranscapes. You're really getting to the nuts and bolts of it. Measuring room RH and temp - find a large leaf on or near to the canopy and use it to shade your temperature probe. RH can be taken from anywhere in the room / tent as you should be circulating the air with an oscillating fan.

[@Terranscapes]

Thanks for the reply. I just started some seedlings and didn't have a fan running. :( Got one going now so humidity should be uniform. The leaf shade is perfect! Will do. :)

[@CottonBoxer]

mainly because if ur humidity is in good range, and your grow temps are also good, the rest will take care of itself with the plants responding accordingly. VPD is a way to go into more detail than most growers need but can still be used to dial in a strain if you're looking to have optimum conditions growing for cash or connoisseur stash. obviously experience,/roper methods/genetics done right has grown bomb plants and always will. but nothing wrong with doing. it better if it matters to someone. i liked the video. yet, with that said i was told when i used to grow not to baby my plants and to keep it simple. best advice i ever got and works wonders for plants as well as living life too.

[@edgarpetrosyan8824]

but wouldnt the IR heat make the leaf hotter than the air, or does the vapor inside the leaf cool it down

[@williamkreth]

Love it

[@mihkel86]

What if my leaf temps are much lower than my room temps? For ex. room is +25C, but leafs are +18C

[@ZHPBrent]

Awesome vid @Everest Fernandez!. I'm doing a VPD grow atm on week 5 if anyone wants to see

[@Just4Growers]

+Cannabis Love Thanks amigo, glad you enjoyed the vid and look forward to tuning in.

[@ZHPBrent]

@Everest Fernandez your channel is my #1 goto for anything grow related. Would be an honor to have someone such as yourself to check out my garden. 👍👍 #growerslove

[@Just4Growers]

+Cannabis Love subbed.

[@rahulsham4014]

Dude, the link to the VPD chart. is that in relation to the plant I think your talking about.. you know, at 4:20 minutes in... lol

[@x5il3ntkilll3rx4]

i love the content keep the great information coming :)

[@jamesmcmillan2656]

Does adding co2 change the vpd ?

[@OmarAhmed-wj8cj]

can you do some videos on some budget LEDs

[@JoshTaylor480]

Ok I'm no math wizard and I can follow the formula up to thr .66 part but where did the 4.5 come from next? I am an HVAC controls guy working on a project and I need to calculate the VPD so I can automate the HVAC. I would appreciate if you could reach out to me on this a little so i can use the formulas properly in my programming code

[@JoshTaylor480]

Oh wait... 10 to the power of 0.6627 is 4.599

[@JohnSmith-fi3vx]

Great video Everest, you're like the Alton Brown of heavily fruiting annuals. I run Illumitex LED lights and the manufacturer recommendation is 12-18" above canopy. I have a temp/humidity meter in one of the pots and another mounted on the wall away from the light. The temp under the lights consistently runs about five degrees higher than ambient. I assume I should be using the under the light temp for my VPD calculations?

[@Just4Growers]

+John Smith Yes, this is the air that is surrounding your plants and the stuff that is interacting with them in terms of the vapor pressure differential. How do your calculations work out? Feel free to post them up if you want to discuss.

[@JohnSmith-fi3vx]

So the long and short of it is my humidity was way too low. I ordered an IR thermometer so I won't know my exact numbers until arrives, but judging by the chart I've been running roughly 20% too dry. I bought a commercial humidifier with an Atlas regulator and have keeping the humidity at the lower range of the VPD chart (assuming a 2 degree difference) and my the leaves look much happier. I did want to ask your opinion on another growing practice that's not really related, because I respect your technical approach. When you're germinating your seeds do you start with peat pellets/pods or the paper towel method? And, do you presoak your seeds? I typically soak my seeds for 12 hours, germinate in a paper towel for a few days, then transplant into a jiffy plug. I recently saw a grower claim that the paper towel ripped micro root hairs off the roots when you remove them, and have encountered multiple sources (usually seed sellers) that claim soaking the seeds is somehow damaging because the water lacks enough oxygen and "water logs" the seeds. Cervantes' book is pro soaking, and even advocates using sandpaper in a matchbox to scratch the seed surface pre-soak, and Rosenthal's texts (the ones I've seen) were kind of ambiguous on the topic. (My apologies if you've already addressed this in an earlier video and I missed it.)

[@eddiebonet7056]

If i'm getting an air temp of 81F and a leaf temp of 66F in 51% humidity, should I still stick with the formulas or default to a 6 degree difference (leaf to air temp) table? The above data puts me in the red (0.34), below 0.4 VPD saying that my plants are drowning, but it sure doesn't feel or look that way. Could I be measuring my air temp incorrectly? Should I shield my thermometer from the lights to correctly measure the air temp? Also for reference, I have the same infrared thermometer you use, and I take an average of a few plants, but the leaves are always within a 1 to 2 degree pocket.

[@Just4Growers]

+Eddie Bonet Hi Eddie, yes, take air temperature in the shade. As you say with your IR thermometer, best to take readings in multiple spots.

[@mo_____2719]

That master grower resume is hilarious. I'm glad I paused to read it

[@Just4Growers]

Empath Finally.... :)

[@torktool]

Mr. Fernandez. What a brilliant video explaining VPD!!!. Super nice work!!!! Could you please suggest any books or tech articles that further explain the history of VPD? Thank you!!!

[@Just4Growers]

+Robert Parelli Sr. Thank you for your feedback. For a historical perspective on VPD try starting with a paper from way back in 1936 called "Relative Humidity or Vapor Pressure Deficit" by Donald B. Anderson from the journal of Ecology. To explore the relationship between VPD and photosynthetic efficiency you have to look to more recent publications. A paper in Field Crops Research entitled "Variability in crop radiation-use efficiency associated with vapor-pressure deficit" by Stockle and Kiniry (published in the '90s I believe) is a good starting point. To get into the current millennium's best scientific thinking on the topic try "Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load" (Guichard,Christian, Leonard, Bertin et al) Journal of Plant Growth Regulation, 2005. Always happy to discuss anything you find in there.

[@torktool]

Mr. Fernandez. I am very honored that you would reply to my comment. Thank you sir. looks like some very good reading on VPD. My wife and i would like to fund you. Please reply with the correct protocol to send some funds to you. Rob

[@Eric-dz1we]

Is there a nighttime vpd chart?

[@frodetyholdt5417]

Great video! As these parameters have an interdependent relationship one can also look at it the other way and adjust the leaf temperature by changing the humidity. At e.g. 25 oC there are many combinations of leaf temperature and humidity that will give you the same VPD. But, they will not be equal in terms of growth. I guess a delta T of around -2 oC is nice to aim for? Also, I am curious on how stable the humidity needs to be controlled. Some humidifiers are really hysteretic and will probably lead to a kind of stomatical yo-yo behavior.

[@CryptoLogicGaming]

can you please explain what you mean by oc? were you referring to -2 oc as in ambient air temp @ 80-f and Leaf surface temp at 78-f, is that what you mean by the -2 oC and if so why a -2 oc? td?

[@mick1963]

Nice job Everest. Excellent explanation of VPD.

[@adrianpoe4416]

I have had an Albo Monstera for a 8 months. In two weeks it’s started browning. Roots look great. I water sparingly every few weeks. Great growth even in winter new leaves. I’m trying to learn about VPD as it relates to browning. I can assume lower temps in winter (73 south fl indoors) are to blame with humidity still at 50%? ZERO info for tropical other than cannabis for VPD levels. Seems that my plant can’t guttate and maybe the stomata gets overloaded trying to release the excess water and it browns. Can someone help me understand this a bit better? I do have a govee meter I bought to measure and keep tabs on temp, humidity, dew pt and VPD.

[@Just4Growers]

Hi Adrian, your air temperature is fine. Albos hate low humidity. You should spray with water regularly. I also suggest watering with distilled water, rather than municipal tap water.

[@danielmacdougall8651]

Hey Everest,A question for you, could you increase the dilution of your nutrient solution to combat excessive transpiration ?

[@Just4Growers]

+Daniel Macdougall Precisely Daniel. I will go into remedial dilution rates in a follow up video. A more dilute nutrient solution helps mitigate the risk of nutrient toxicities when faced with high VPDs. Similarly, growers faced with cool temperatures and low VPDs increase their nutrient strength.

[@gulstan6007]

Brilliant Everest brilliant

[@jimhamilton597]

Hey buddy! your videos are awesome! what's the best most economical way you've found to increase root mass in Rockwool? im thinking about topfeeding with tea every week or so in veg.... know tea makes Roots explode but don't know if it could gunk the Rockwool up. I'm in drain to waste... sounds good but I dont hear about other growers doing it (What are the big veggie greenhouse guys doing?). If it matters im looking for a rooting solution I can implement in a 7,000sf facility ;)

[@Just4Growers]

+Jim Hamilton Hello Jim, I am so glad that you stopped by! Which rockwool product are you rooting into? 3" or 4" blocks? Loose fill? Or Hugos? Tea with rockwool? Not something I've tried. I'd worry the risks outweigh the benefits. Better to focus on correctly timing the irrigations so the rockwool has a proper wet / 50% dry cycle with well arrayed, good quality mineral nutrients. Perhaps a root stim like accerlurator or rapid start. Raise the blocks or pots up too to allow for some air pruning action. Anyway, I'm keen to learn more about your set-up. Are you on the west coast?

[@jimhamilton597]

Everest Fernandez - Hey! I'm in Maine, I clone in the normal grogan plugs (1.5-2") and use the Hugo blocks using a dtw system. Working on the irrigation and think im doing well with it but will be buying a grosens meter soon i think (only like $2500 ha) to really dial it in. I'm interested in a root stimulant, but leaning towards beneficials... most readily avaliable root boosters are unnecessarily expensive though, so wondering what the big veggie growers using if anything.... Have hard about raising the blocks but commercially this just means more equipment to clean constantly and more man hours which is expensive. you mentioned the teas could be 'risky' what risks do you see? I have used it before in soil and expecially in bubble buckets you see the roots go CRAZY like immediately with 1-3 days later roots undeniably going wild... so would love to try it on RW and it is soooo cheap to make! going to have to experiment top feeding every week or two at last through the first couple weeks of flower

[@andyhang3545]

Best video on VPD by far! Thank you ! Quick question, measuring kPa instead of millibars gives you a more accurate VPD reading for plants right?

[@Just4Growers]

+Andy Hang Thanks. No, kPa is just millibars / 10. It's just a matter of preference which unit you use.

[@luminox138]

Hello, what formula did you use in the equations to obtain the VPD? Any reference from any author?

[@Just4Growers]

Monteith J. L. and Unsworth M. H.(2007). Section 2.1. Gas and water vapor. In: Monteith, J. L. and Unsworth, M. H.(Eds.). Principles of environmental physics. 3rd edition. Academic Press, pp: 440.

[@RobMyself]

Hey Amigo! Back again. Quick question: Does VDP matter at night (or lights out)? If it's needed for transporation that encourages photosynthesis, then does it really matter when there's no light? I'm thinking you'd want fairly the same at lights on as lights off, but when the lights are off, that VDP drops. So I'm thinking ease up on the RH when thoughts are out. Am i correct? You might have mentioned this while I was typing haha.... My new light and controller has incredible versatility and control, so I trigger fan, humidifier, etc. based on a target VDP. Lights on, I've been bullseye spot on, but I'm curious if i need to adjust with lights out. Still the best and most informative KZbin growing channel. My only complaint is i wish the was more content! 😁

[@Just4Growers]

Does VPD matter at night (or lights out)? : Yes, Vapor Pressure Deficit (VPD) still matters at night, but its importance shifts. During the day, VPD primarily affects transpiration rates and, consequently, photosynthesis and plant growth. At night, plants do not photosynthesize, but they still respire and transpire, albeit at reduced rates. Proper VPD management at night helps avoid issues like mold, mildew, and other pathogens, which thrive in conditions of high humidity and low airflow. If it's needed for transpiration that encourages photosynthesis, then does it really matter when there's no light? : Even without light, transpiration continues, though at a lower rate. The stomata (pores on the leaves) do not fully close at night, so some water vapor is still lost through transpiration. Maintaining an appropriate VPD at night ensures that plants do not become too stressed and helps maintain overall plant health by preventing excessively high humidity that could promote fungal growth. I'm thinking you'd want fairly the same at lights on as lights off, but when the lights are off, that VPD drops. So I'm thinking ease up on the RH when lights are out. Am I correct? : You are partially correct. While the target VPD may not need to be identical during the day and night, maintaining a balanced VPD at night is still crucial. When the lights go off, the temperature drops, and if the relative humidity (RH) remains high, VPD can drop too low, potentially creating an environment conducive to mold and mildew. To avoid this, it’s advisable to slightly reduce RH at night to maintain an appropriate VPD level. Practical Considerations at night: Monitor Night Conditions: Use sensors to continuously monitor temperature and humidity at night to maintain appropriate VPD levels. Adjust Humidity Control Systems: If your system controls RH, ensure it can adjust for nighttime conditions by lowering humidity slightly when the lights are off. Airflow and Ventilation: Ensure good airflow and ventilation to prevent excessive humidity build-up, which can lower VPD too much.

[@RobMyself]

@@Just4Growers Thank you for the detailed reply. Got it! You're the best.

[@RobMyself]

@@Just4Growers And yes. My control, at the current stage, the VDP is set at 1.12. but I've noticed it fluctuates between .93 to 1.12 with an average temp of 77. So I think I'm right on target. They look super happy so I'm thinking it's working. And the air exchange is moving perfectly! Inline fan blowing it out, with passive intake from the bottom. Two fans low and one on the light itself and in oscillating fan between the lights and the tops of the plants. It's heaven! 😂

[@ConjointVR]

Hey how can I transplant auto flowers into a bigger pot with the least amount of shock possible?

[@Just4Growers]

+Meme Dealer let the root zone dry out quite a lot - should only take a day or so if the plants are ready for transplant. Then you should be able to pop them out of their pots much more easily.

[@eddiebonet7056]

What should the VPD be for the night cycle? Is it meaningless at night? Or should we just keep it above 0.4?

[@Just4Growers]

+Eddie Bonet That’s an awesome question Eddie. Thanks for asking. Many plants (not just C4 but C3 species too) transpire at night - I.e. they do not fully close their stomata so some water loss still occurs. Typically 5-15% of daytime water loss rates but sometimes higher. VPDs are typically lower at night because of lower temperatures. So, while it’s not meaningless, I would say just keep your grow room’s air movement going through the night and don’t let humidity spike too high - probably more at risk of low VPD than high VPD at night - 0.4 for propagation / early veg fine day or night. Stomata are almost closed so it’s not such a big deal.

[@HHJoshHH]

Dammit I love your videos Everest. I wish I could talk to you in person. I have so many questions that are so specific, plus I love to talk gardening and gardens. Sigh. A gardener can dream. 🙂

[@Just4Growers]

Thank you! You are welcome to email me any time amigo: [e-mail]

[@HHJoshHH]

@@Just4Growers just sent you an email! Ty so much Everest! 🌱❤️🌱

[@MrAsternine]

Does the vpd chart change if you're growing in a hydroponic system?

[@Just4Growers]

MrAsternine No.

[@meefvongrau9814]

0:40 how do you call this?

[@danielmacdougall8651]

Love your sense of humour, kind of pythonesque. Cheers !

[@Just4Growers]

+Daniel Macdougall showing my British roots! :)

[@murrmovies]

Thanks Everest! Great explanation. Question. Does the VPD chart apply to all plants? Or are there different variables depending on the type of crop?

[@chris432t6]

Why were we taught in school that Fahrenheit was air temperature and Celsius was liquid or water temperature? Cannot tell you how frustrating and confusing this has been? Cool video regardless.

[@drunkrtard]

Why would you ever find air temp above leaf temp?

[@mohsenaghdam3136]

O Jesus you are Einstein of Hydroponic The father of hydroponic❤️❤️❤️❤️👍🏽🤘🏽

[@kazimir8086]

What would happen if I double or halve the atmospheric pressure? Like could it be beneficial?

[@Just4Growers]

InnocentPhoto when you go higher, atmospheric pressure decreases because the air is thinner. This increases the VPD because there’s a bigger difference between the vapor pressure in the plant and the surrounding air. It’s really not a question of being beneficial or not but keeping nutrient strength in balance (especially calcium) with the extra transpiration that will result from a higher VPD.

[@N1kRolexx]

Everest, is distilled water good for preparing nutrient solution for hydroponics?

[@jdlitson]

Yes, distilled, or reverse osmosis (RO) water is good. Since they contain zero to very minimal; mineral content you will need to add twice as much calcium magnesium supplement than you would add to tap water. What is the EC or PPM of your tap water?

[@N1kRolexx]

Hi, just today received my TDS meter. My tap water is at around 220ppm. What nutrients with Calcium and Magnesium do you recommend?

[@paulfun8720]

Who knew there was so much damn math in growing weed. This is more complicated than Euro Asian EC meters for sure man. Where is the damned VPD online calculator tools? Now I am going to have to take a super deep dive into how the formula was derived. This should only take me a year to fully understand.