Vapor Pressure Deficit
The ideal environment for your plants.
Introduction
You probably already have some idea of what Vapor Pressure Deficit is, but maybe you need a simple introduction, with no formulas or math. We got you covered, plus we’ll give you calculators, recommended ranges, and easy to use reference charts!
At some point, most indoor growers run into some mysterious plant growth problems, ranging from symptoms that look like nutrient deficiencies, when the nutrients are actually perfectly balanced and fresh. Or sometimes a cultivator sees sluggish growth, or powdery mildew, to a whole host of unanswered questions that in fact relate back to the environment!
The amazing thing is, adjusting for this one thing, Vapor Pressure Deficit (VPD) can create the ideal environment for your plants to thrive in. This is a pretty cool and slightly advanced concept that can take you to the next level. Once you understand it and apply the concepts, you’ll see your garden improve in a big way.
So if you’re ready to create the absolute best environment for your plants, read on and we’ll dive right in.
Concepts
Vapor Pressure Deficit measures the amount of drying power the air has upon the plant. Basically, it’s how much moisture is being sucked out of the plant by the atmosphere.
You probably already know the plant uses transpiration to grow. Literally, the plant will die if it can’t release moisture through its stomata. The process of transpiration in plants is similar to how we sweat; they have stomata which are similar to our pores. But the big difference is, they do this so they can pull in more liquids through their roots to fuel photosynthesis.
When Vapor Pressure Deficit is too high, the plants might not be able to keep up with the environmental demand upon them. The air is drying them out too fast! And this will cause them to exhibit symptoms that look just like nutrient deficiencies, and the plant will grow poorly.
On the other end of the spectrum, if Vapor Pressure Deficit is too low the plants can’t transpire. Moisture may build up on the leaves, and the plant will grow much more slowly. If this goes unchecked for too long, the plants might get attacked by molds and fungi, like powdery mildew.
Reading up on VPD you’ll see all sorts of measurements of Vapor Pressure. There’s Saturated Vapor Pressure (SVP), Atmospheric Vapor Pressure Deficit (AVPD), Leaf Vapor Pressure Deficit (LVPD), plus several others not worth mentioning.
Vapor Pressure Deficit is the difference between the Saturated Vapor Pressure (SVP) and Relative Humidity. Saturated Vapor Pressure is the maximum amount of moisture the atmosphere can hold according to it’s temperature. And Relative Humidity is the amount of moisture currently suspended in the air. So to calculate the room’s Vapor Pressure Deficit all you need is two measurements, temperature and relative humidity!
But this isn’t the whole story. The plant’s experience is slightly different because they are usually a bit cooler than the room. If the plant temperature is exactly the same as the room temperature, then the plant and room Vapor Pressure Deficit levels are equivalent. But this is rarely the case! Usually, the leaves are between 3° and 5° F cooler than the room because they are transpiring. The evaporation on the leaf’s surface literally draws heat from the leaf, thereby cooling it.
We call this Leaf Vapor Pressure Deficit (LVPD), and we need only one more measurement to figure it out, and that’s the leaf temperature of the plants. To get this measurement we use an infrared thermometer (IR thermometer), and they are rather inexpensive, there are dozens available on Amazon for under $30. It’s so easy to take the temperature of anything with an infrared thermometer, like ballasts and reflectors. So if you’re like us, you’ll start pointing it at everything in sight.
So while the room’s Vapor Pressure Deficit is important, we really want to focus on what’s going on within the plant. That means we want to know the Leaf Vapor Pressure Deficit because we’re trying to grow the best and biggest harvest possible, right? Right!
Here’s a good place to give you our first gift of this post, the Room and Leaf Vapor Pressure Calculator:
Leaf VPD Calculator
More Details and Specifics
It’s important to note that the different parts of the plant are going to be at different temperatures. You’ll see this once you start using your IR thermometer.
This all sounds wonderful, until you’re doing it daily, multiple times per day… and then there’s the dark period! How do you do that too!?
Well, Dimlux has you covered with the Maxi Controller, which can automate the measurement process for you when it has a thermometer, humidity meter, and Plant Temperature Camera. In fact, the Maxi Controller Data Logger will keep track of all of this for you on a spreadsheet so you can see if you’re having swings in your Vapor Pressure Deficit when you’re not around to catch the problem!
We highly recommend the Maxi Controller Data Logger with all the add ons, obviously.
Plants can grow within a wide Leaf Vapor Pressure Deficit range, somewhere between 0.4 and 1.6 kPa.
The ideal level of Vapor Pressure Deficit changes during a plants life cycle. Clones need a super low Vapor Pressure Deficit to grow roots, otherwise they’ll just dry up and die. Large plants in late flowering, tend to produce much better harvests when the Vapor Pressure Deficit is on the high end of the range, stressing them a bit. Also, a slightly drier atmosphere will inhibit powdery mildew and mold.
Recommended Leaf Vapor Pressure Deficit
Assuming leaf temperature 5° F (2.8° C) below room temp.
| Plant Cycle Stage | Min Leaf VPD | Max Leaf VPD | Temperature | Relative Humidity |
|---|---|---|---|---|
| Propagation / Early Veg | 0.8 kPa | 1.0 kPa | 70° F | 60% |
| Late Veg / Early Flower | 1.0 kPa | 1.2 kPa | 75° F | 50% |
| Mid / Late Flower | 1.2 kPa | 1.6 kPa | 75° F | 40% |
Here are the Leaf Vapor Pressure Deficit numbers we recommend over the plant’s life cycle. Keep in mind, different strains are going to be a little different than one another. Also, you need to make sure your instruments are calibrated and giving you accurate readings. If you can’t trust your instruments, then the Vapor Pressure Deficit number you calculate is useless.
We’ll leave you with the biggest set of VPD Charts we know of, so you can just take the measurements and reference the correct color coded VPD Chart adjusted for leaf temperature.
These will help guide you to maintain the best humidity and temperature levels in your grow room for each stage the plants are in. You can select the chart corresponding to the temperature the leaf is below room temperature, anywhere from 0° to 5° F. Move the mouse over the temperatures below each chart and notice how much the chart changes based on a few degrees change in the plant’s temperature.
DOWNLOAD THE PRINTABLE VPD CHARTS PDF
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Formulas
There are several ways to calculate Vapor Pressure Deficit, but the specific formulas are beyond the scope of this article. Especially since we made that really nice Leaf Vapor Pressure Deficit calculator and the LVPD Charts for you. If you reeeaaaaalllllyyy want those formulas, check the source links we provide at the bottom of our post. A few of the formulas you can just plug right into a spreadsheet like Google Sheets or Excel.
Why do I see VPD represented by all sorts of different measurements?!
Because Vapor Pressure Deficit is by definition a measurement of pressure, there are several numbers that represent it. The most popular is Pascals (Pa), which is usually too large of a number so we take it down to kiloPascals (kPa). For completeness, 100 Pa = 1 hPa = 0.1 kPa. Moreover, 1 hectoPascal (hPa) is equivalent to 1 millibar (mb). Why the different names? Well, the name was changed to honor the scientist that discovered it. We do the same thing with Volts, Amperes, Ohms, Watts, Joules, Hertz, Celsius, and Fahrenheit. Sometimes pressure is measured in pounds per square foot, or kilos per square meter. But in our case we’re going with kiloPascals (kPa) because it will give us clean whole numbers to work with that match the Maxi Controller.
Sources:
- Quest Dehumidifiers – Vapor Pressure Deficit Series: Part 1, Part 2, & Part 3
- Desert Aire – Vapor Pressure Deficit & HVAC Design PDF
- National Weather Service – Vapor Pressure Deficit formulas PDF
- Alchima – Vapor Pressure Deficit in Cannabis Cultivation
- The Weather Window – Hectopascals & Millibars are they different?
74 Responses
This is now my go to for vpd reference. I’m a science guy. Meters and controllers for everything. Your chart and the wave of change over time are great.
The leaf vpd calculator(I was using an IR thermometer already, low 80s with a QB works well. ) is awesome.
Thanks! I’m glad you found our tools and charts useful Greg.
I am trying to find out what an acceptable swing in VPD is. Sometimes the humidity is fluctuating +/- 2% and that causes VPD to fluctuate .6 kpa. Before I got a controller I was oblivious to these things. Now that I’m seeing it I OCD on minimizing the fluctuations. Is .6 kpa a reasonable fluctuation? At what point should I be concerned.
No doubt Greg !!! This is the best reference I’ve seen so far.. Such a clearer understanding for sure.. NICE WORK GUYS!!!!
This is awesome! I’m a total beginner and I didn’t know much about VPD before, other than leaf temp should be lower than room temp. Thank you for doing this, I think it will help me a lot.
Can you tell me how to calibrate the temperature probes for the dimlux controllers ? I’ve tried steam and ice but this didn’t work .
I have two controllers to control my HPS and CMH lights seperately but the probes give me different temperatures readings (around 2 oC difference, and around 4 oC difference from my opticlimate probe !)
For North American customers, please contact us directly for technical assistance on calibrating your Dimlux products. We’ll love to make sure it’s all working great for you.
The chart is helping I’m just confused I started growing outside now. I’m intense and this is a new concept to me if anybody has the same problem please. Or some help thanks
How’s it going . I’m still trying tony derstsnd the VPD chart . Say my lights are on , temp 78 degrees early veg , humidity 49% . That’s good or bad .
Would I adjust the A/c temp or Light Percentage Higher or lower( Using Gavitas) . To change the humidity ??
Usually we use Humidifiers and Dehumidifiers to adjust the humidity in a room. And we use AC or heaters to adjust temperature. In extreme cases we adjust the light intensity to cool a room. Optimal Light intensity is another conversation. Basically, there is a range where plants grow best (can be different for different species), anywhere in that range will produce excellent growth for you plants. Check out our article on Half Force for information on light.
This is the best VPD chart I’ve seen. Very easy to use and informative. Thank you.
Great chart!
There is a large temperatures / humidity variance for optimum VPD.
In flower is it better to start off at a higher/temp and slowly reducing the temp/humidity? say starting at 80degrees/60% humidity and then ending at 70degrees 35% Humidity in some linear fashion? Or is it better to start at 75 degrees 60% humidity and just reduce the humidity to 40% by harvest?
What should the night temp and humidity be? Just follow the vpd chart?
Thanks
Hi Pete,
Follow the recommendations on the upper right of the chart for the various plant stages. You should think in terms of kPa instead, but yes, either one of those scenarios you proposed fit in with what I recommend in the chart. Keep things under control at night too. Follow the chart!
K
Is it possible to create a positive offset on the chart as the hps bulbs heat up the plant leaves 2-3C more than the room temps
Hello Andrew,
Have you considered taking leaf temperatures from other parts of the plant? Or conversely taking the air temperature from the canopy where you’re getting your leaf temp from?
The leaves should always be cooler due to transpiration.
Let me know if this clears it up for you.
K
I’ve tried many different areas on the plants. still, right now, I am getting 1C difference higher temps on the veg plants. From 23-26C room temp, and the leaf temp follows the room temp. The humidity in the room is about 70% daytime and 80% at night. And the calculator shows the leaf RH to be around 1.0vpd which is ball park of where we want to be. I just cannot get the leaf temp lower than the room temp. MH 1000DE (6k color) are 3’ away with about 280umoles. I really think it’s the Infrared heating up the plants leaf temp. Not sure what else to think…
This is really odd. I understand what you’re saying in regards to the radiant heat of the lights heating the leaves up, but in my experience the leaves have always been cooler than the air due to transpiration. Have you verified this with different thermometers? I’ve had the misfortune of using defective thermometers before. And I’m sure you’re taking the air temperature around the leaves as well, right? Rather than the air temp somewhere in the room that’s cooler. We want to measure the plant’s living environment… I’m running out of ideas to help though…
Raise the lights some?? Just guessing.
I would definitely recommend redundancy with your measurement instruments. Double checking accuracy with a second instrument should help clear things up, or at least confirm that your readings are correct. I use LED and they’re obviously quite a bit cooler but I’ve never had leaf Temps be closer than 2 degrees below room temp. I have my LEDs at 14″ from canopy.
Have you tried to get a temperature reading from the underside of the leaf?
perso j ai eu le cas ce matin ou les feuilles etait pkus chaude que l air ambiant, mais je pense comprendre d’ou cela vient dans mon cas, cela c’est produit lors d’une chute brutal des temperatures durant la nuit ( en 12h la temperature de la box qui etait stable depuis des semaines a 290c, est passé en 12h de 29°c a 24°C, je pense que le froid brusque de l auonmne qui et arrive hiers, a refroidi plus rapidement l air de la box que les plantes qui n on pas elle, refroidi si vite, donc je vais reverifier ce soir, , j imagine que sur un climat stable , les feuilles ne peuvent pa (en theorie etre plus chaude ue l air, mais en cas de chute rapide des temperature, les plantes mettent sans doute plus de temps a refrodir que l atmosphere de la box(?)….(a suivre). mais je vais quand meme testé un autre thermometre laser, des foie que mon thermometre serai a l ouest…
A lot of IR thermometers tell you not to measure in direct UV light try turning your lights off when you measure really quickly to get more accurate measurement , and also take several on different parts of the plants going with the average. If not time to recalibrate
yes MH and HPS lights have lots of unusable spectrum, those photons are absorbed by the plant and their energy converted to heat – under MH/HPS bulbs your leaf temps can be up to 15 degrees higher than ambient
this is false – plant leaves absorb photons from the unusable spectrum of a light and convert it to heat – a plants LST will be anywhere from 2-15 degrees higher than the ambient temperature depending on the type of light being used. See this experiment – https://www.blackdogled.com/pages/lst
I would love to have someone explain this chart to me, trying to get a handle of using this chart. The chart mentioned here shows numbers that is confusing me is it the room temp. or the leaf temp that I go by?? For ex. my plants are 3 1/2 weeks old from seed the room temp is at 72F, humidity is at 60% and the leaf temp. is at 70-73f???
Hi Ray,
The temperatures on the chart represent the room’s temp. There are six charts, each representing a different leaf temp. The leaves should be cooler than the room due to transpiration. So this difference is represented at the top of the chart, “Leaf cooler than the room by” 0, 1, 2, 3, 4, and 5.
The room temperature will be different in different places. It’s probably a good idea to take the air temperature near where you’re taking your leaf temperature readings to get an accurate difference. It won’t make much sense to take the ambient room temperature someplace that’s cooler, and then a canopy leaf surface temp directly under the light.
Let me know if that helps!
K
What about having multiple plants, how would one do this
Several measurements and some averages. Use fans to circulate the air so the temps across the room are more consistent. This is usually done with many plants in a large greenhouse.
Would all these charts (6) all work for various tropical plants , to greenhouse vegetables, to house plants , to outdoor field crops/ berries etc. , or are these VPD charts geared to cannabis only ?
Good question. It’s going to be different for different plants. Tropical plants will likely have a different VPD range that they do best in.
I’ve read many interpretations on VPD. This is, by far, the clearest and most informative. More importantly, it is as layman’s as possible. I especially like the chart variations when taking leaf temps into account. Excellent write up!
Would it be best to hang the humidity/temperature sensor at canopy height, under the lamps?
It’s better to have good air circulation so the temperature is more consistent around the room. But if this isn’t possible, you want to get an idea of the temperature the air is immediately around the plants. Canopy is the place temps are usually measured. VPD is a guide and the temps are another guide to understanding what the plants are experiencing. These aren’t hard rules. So you’ll need to use some intuition along the way. And you’ll get better with time.
Does nighttime VPD matter as well? It’s hard to keep the temps and humidity the same once lights turn off. the air conditioners drop the ambient air a lot and the dehumidifier setting doesn’t change, which will create a pretty low vpd unless a heater is brought in. Thoughts?
For sure! Keeping VPD in check is important all of the time. We don’t want moisture gathering on the leaves overnight! That will create perfect environment for powdery mildew (or other fungi) to take hold. And I don’t know anyone that wants powdery mildew. Gross.
I’m sorry I’m new at this. My temperature is 84°. My humidity is 48.2 and my VPD is at 2.0 I have one circulatory fan and vent fan and the duck system in a 2 x 2 x 4 tent with a 1000 SE LED light is there anyway to lower the temperature how can I bring the temperature down?
Hello, if I already have my vpd given to me on my master control , but I don’t have my leaf temp what chart do I use? Or do I have to get the temp of the leafs
Good question. Choose a chart where the leaf temperature a 3 to 5 degrees below the room temp. This is the typical range you’ll measure the leaf temps once you get an infrared thermometer.
I’ve seen some other charts from 2021 recommending 50‐60% for late flower opposed to 40-50% recommended here.
ce n est pas de la mecanique , tu travailles avec du vivant , ‘c ‘est comme nous perso j aime les climats chaud alors que ma soeur deteste la chaleur et n est bien que l hivers quand l fait froid, donc ce n est pas des regles exactes, ce n est pas 10% de difference d’humidtée qui va changer enormement les choses , mais il faux s adapter en fonction de comment la plante reagie, certaine seront au top a 55% d humidite et il se peux que sa voisine prefere un 40% mais entre 40% 50% tu as peu de risque de moisissure, a plus de 70% par contre là oui,10% de difference peut te faire foirer ta recolte en tamenant des moisissures.
Hi, Do I follow the same VPD charts for nighttime? IF not, what #’s should I be going for? Thanks
Hey, Scratch previous comment as I know it’s not the same because I always bring my humidity down at dark. The question is more accurately, What LVPD should I run at night?
Thanks
B
Hi i have 5 led lights with opticlimate and is good when temp hit a set up point on controller then my leaf tem is exactly 2.8 degres lower like room temp,but opti turn on every 7min and then drop down leaf temp to over 6 degres is that still ok?
I have been using this chart for about 4years now and all I can say is, its clearly the BEST VPD chart out there and I just got the PulseOne Pro a year ago and this chart is its girl friend they go hand to hand with readings. I have issues with readings when close to harvesting so I have learned to go on instinct about 3-4 weeks sometime the last 2 weeks to go on the high end of the readings. Keep doing the awesome work your doing. PS I am thinking about getting lights from this company…
Nice chart.
I’ve tried to print it but its to smal. I also tried to get the printer friendly version via mail but I have not received one yet even though I’ve tried twice.
Am I doing something wrong?
I found mine in the Trash folder and it downloaded and printed beautifully. Thanks Kris for the chart, it really helps me get control of my tent’s environment for optimal growth.
Before I print this I need to take measures to see the difference between room temp and leaf temp and then choose the chart that matches?
Hi Jimbo – Please accept our apologies. We haven’t had a moderator on this website for quite some time. We did not realize the VPD chart form was not working. I will look into that now. I will also email you the VPD charts. Please look for an email from Global Garden. You will have it today.
Does vpd and DLI work together. I have been growing now indoors for about 22 years. When I first started I was using 2 600 watt hps and well water and fox farm ocean forest. I never ph my water and I never gave it any nutes. Keep the temps under 80 but never really worried about the rh % either. I also have 6 inch exhaust and a 4 inch intake. I would pull about 2 lbs out of a 4*4 tent which I was ok with. I did try giving it fox farm nutes but I never noticed a difference. Well in the last few years my location has changed and so hasn’t my growing equipment but now I’m having issues. And of course everyone else thinks it is something different from the last person. So I’ve been doing a ton of research and I’m almost 100% sure I am getting some type of lockout. But I’m not sure what is causing it. I’m pretty the vpd being out of the proper zone didn’t help but these new lights are so intense I have my 240watt actual draw about 20inch above it but with out a meter it is hard to tell if I’m just wasting light and or hurting the plant. I have adjusted the vpd to be close to the proper kpa for the cycle I’m in and I just ordered a ppfd light meter so I can fan out if I’m getting the proper ppfd and DLI. If that isn’t it it could be the water that I’m using now cause it is a different grow. But hopefully I’m heading in the right direction and I know what is like to have a beautiful successful harvest of top shelf cannabis. So when you start having issues you really find out how delicate cannabis really is but at the same time being very resilient. I’m also convinced that I was just extremely lucky on my initials grows. But anyways happy growing everyone.
Your ultimate guide to Vapor Pressure Deficit (VPD) is a treasure trove for indoor gardeners. The in-depth explanation of VPD’s impact on plant growth is insightful. Consider incorporating case studies or success stories to showcase real-world results. Your commitment to shedding light on optimal growing conditions is evident throughout the article.
thank you for this useful article
when the tips of the leaves have tendancy to “cower” to the top, instead of staying right or to cower slightly to the bottom (optimal transpiration), does this means the air is a bit too dry ?
this a bit technical question but people having experience would be able to tell
I think it means transpiration is a bit too high and the plants are trying to reduce leaves surface exposed to sun/light
it also happen to clones when you quickly open the dome in a dry room
waz just looking for the charts.i learned alotanout vpd just reading above.u have alot of imfo geetinh out to new guys thereand u can undersrand the way u put it out there.thsnks.good kob
My VPD is too high at about 1.8 or 1.9 with a temp of about 75 degrees F and humidity of about 50%. How do I bring the VPD down during the light cycle. Seems to be in perfect range at night at about 1.3. Any advice?
Does any this factor in co2 enrichment ?
Thank you to whoever put this up. Legends the lot of you
This is what I’ve been looking for thanks
I find it very hard to accept your terms of privacy when I cannot even see them.
Waited a long time for this , I check my meteorology with my morning smoke and coffee , I pair the weather forecast to my vivosun e42a via phone app manually, using the leaf temp variable will hopefully increase resins
Is this based on ambient co2 levels as the vpd sweet spot changes as ppm increases.. not trying to factor in extra co2 ATM but eventually a vpd calc with the ability to input CO2 ppm would be a game changer
First of, very nice work and highly appreciated. But since I’m a RDWC Nerd, I was wondering how to determine a. The actual phase of the plants and b. The sweetspot within to set the right VPD, especially with the accelerated growth combined with the higher transpiration rates within deep water culture units. The only indication I could inspect was the “pray posture” of the leaves stretching towards the light.
And following this observation, I could determine that RDWC needs much dryer conditions throughout the whole growth, since we reach 2x-2,5x the transpiration rate, compared to Soil (1x), Coco (1,5x) or Rockwool (1,5-1,75x), which would also explain the explosiv growth.
Do you have any other indications how to determine the sweetspot?
I’ve been using an IR thermometer with my QB setup too, but I hadn’t thought to combine it with a leaf VPD calculator—that’s a game changer. Your point about the wave of change over time really clicked for me; it’s easy to get stuck on a single reading instead of watching the trend.
I appreciate how you’ve made VPD tracking so accessible with that leaf calculator—I’ve been using an IR thermometer too and seeing those low 80s readings with my QB setup. The visual representation of VPD changes over time really helps me understand what’s actually happening in my environment rather than just chasing numbers. Definitely bookmarking this as my reference guide going forward.
Man, I’m with you on being a science geek about this stuff. That leaf VPD calculator is a game-changer—I was already using an IR thermometer too, but seeing how the leaf temp actually shifts the VPD numbers really dials things in. The wave of change over time graph is what clicked it all together for me.
Using an IR thermometer to dial in that leaf VPD calculator has completely changed how I manage my grow under my Quantum Boards. Keeping the leaf temps in the low 80s is so much easier now that I can visualize the wave of change over time with your chart. It’s awesome to see how using proper meters and controllers can take the guesswork out of the equation.
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I totally agree with Greg about the leaf VPD calculator—using an IR thermometer to get those leaf temps is a game changer, especially when running QBs in the low 80s. Seeing the “wave of change over time” visualized in the chart really helps make sense of all the data from the controllers. It’s awesome to have such a solid VPD reference that actually appeals to the science-heavy side of growing.
I’ve also been using an IR thermometer to dial in leaf temps under my quantum boards, and it really changes the game. That wave of change chart is super helpful for visualizing how VPD fluctuates throughout the day instead of just looking at static numbers. Having the leaf VPD calculator handy makes it so much easier to adjust the controllers on the fly.
I’ve also been using an IR thermometer to dial in leaf temps under my QBs, but having a dedicated leaf VPD calculator to pair with those readings makes a huge difference. The wave of change chart Greg mentioned is also super helpful for visualizing how things shift throughout the day rather than just looking at static numbers. It really helps when trying to program controllers for a more dynamic environment.
I’ve also been using an IR thermometer to dial in my leaf temps under a QB, so having a dedicated leaf VPD calculator here is incredibly helpful. The way the chart illustrates the wave of change over time really helps visualize the daily fluctuations. It’s awesome to find a resource that bridges the science with practical growing setups like this.
Using an IR thermometer to get actual leaf temps is such a game changer, especially when running Quantum Boards since they run so much cooler than traditional lights. The leaf VPD calculator here makes it incredibly easy to dial in the environment instead of just guessing. That chart showing the wave of change over time really helps visualize how to adjust settings throughout the day.
I agree with Greg about the leaf VPD calculator—using an IR thermometer to get actual leaf temps makes a massive difference compared to just guessing based on ambient air. The way this guide visualizes the wave of change over time really helps conceptualize how to adjust controllers throughout the day. It’s easily one of the most practical resources I’ve found for dialing in a grow room.
Like Greg, I’ve found the leaf VPD calculator to be a game-changer, especially when paired with an IR thermometer to get accurate leaf temps. The chart showing the wave of change over time really helps visualize how the environment fluctuates throughout the day. It’s definitely helped me keep my room in that sweet spot in the low 80s under my QBs.
I’ve also been using an IR thermometer to check leaf temps with my QB setup, and Greg is spot on about keeping it in the low 80s. That leaf VPD calculator makes it so much easier to dial in the environment instead of just guessing. The chart showing the wave of change over time really helps visualize how the room fluctuates throughout the day.