I’m not sure who follows VPD but it’s one of the most important things to follow. Follow it and say good bye to bud rot and PM. Also grow danker buds.
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I totally agree! Learn to control it. It’s a game changer.
Vpd is complex, vpd with LEDs is more complex, and how each plant handles VPD makes it something of a nightmare for someone like me who doesn’t use the same cut more than twice.
I want to understand, but I just don’t have the time and resources. Forums are great, but the knowledge is often scattered and conflicting, articles are hit and miss, with mostly misses. I’d like a book on the matter if I could get my hands on one and have the time to read it.
For instance, the lack of IR in LEDs produces a lower leaf surface temp than the sun or a HPS bulb, meaning the ambient temp has to be higher, but I have no idea if my sensor accounts for that, or how to do the math myself.
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It’s a puzzle, for sure. Another thing to add to the list of things to understand about successfully growing quality cannabis; light, water, heat, RH, airflow, nutes, mediums, etc. Not every environment is the same, or easy to control. Not every method is equal to every other method to control those things. It takes time to figure out what works best for your specific situation. However, once you master your environment, it all starts to become a whole lot easier.
A lot of LED boards available today are a joke, but there are some that can provide close to the level of of intensity and heat that an HID can. The best I’ve used so far are the High Light 420 from Grow Lights Australia, but I’m sure there are others that can compare. Mine are 480W each. They (4 of them) reliably raise the temp in the room (11 ft x 7 ft) by about 10 degrees. I set a heater to keep the night temp at ten degrees lower than what I want my day temp to be. The intensity of these lights is serious. If they’re too close to the canopy, the canopy will bleach out. I have a light meter and keep the distance of the lights from the canopy based on the PPFD measurement being between 800 and 1100, depending on the plant stage and the leaf temp. I test the canopy leaf temp using an infrared thermometer.
If you can’t afford the lights, you can use a ceramic heat emitter to attain the 1 or 2 degree difference at the canopy. However, without the correct light intensity and spectrum, maximum photosynthesis won’t happen. That’s a different discussion.
VPD was the most difficult thing for me to control. I could control everything else, but VPD was elusive. Nothing provided the amount of humidity necessary until I found a DIY fogger that I paired with an Inkbird humidity controller. Now I can easily hit any VPD level I need, and maintain it. Google the house of hydro fogger diy humidifier instructions. There are small, 3 disc kits on Amazon. It’s a game changer. The plant turns into an engine, making optimum use of nutrients through maximizing transpiration. The math behind it really isn’t as important as maintaining an optimal environment.
I use this chart to understand and maintain my levels.
I’ve almost never grown the same strain twice. In my experience, very few strains react differently than every other strain to optimal VPD. Those that have reacted differently didn’t require much change, either up or down in humidity to be happy, and the other plants in the room weren’t bothered by the new level maintained.
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This is a really nice site…maybe they all have the same features, but being able to scroll and set air temp, leaf temp, rh is convenient.
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might be unpopular but i actually dislike the use of vpd, and it’s because of the variances in genetics. vpd charts aren’t accurate for landrace or pure sativas in my experience. maybe it’s my environment or something i’m not aware of. i’ve also heard vpd charts are terrible for fully auto strains but that’s just what i’ve heard.
my opinion is that it’s made as a crude tool to give an idea for what’s ideal, but in practice i never found results following it. i hope others do if it works for them great!
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My VPD is only ever right by accident. I have no control over my temp and RH and have no choice but to let them do their thing. Works fine.
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The biggest factor for me in controlling VPD was no more powdery mildew and no more bud rot. I run around 1 in Veg and up to 1.5 gradually as flowers mature. I have a de humidifier in my lung room and a humidifier in the tent to achieve this. I grow a lot of different strains at once quite a bit and the benefits are in deniable.
I also learned to run my lights at 50% in veg and bump up to maybe 70% during flower. Without CO2 they are too bright and it screws the plants up. When you see the top buds are smaller than lower ones that’s a sure sign it’s too bright.
That’s exactly what I use. I’m only able to keep things dialed in the lung room during the cooler parts of the year to control the tent environment. During the summer I just shut down. I’m not willing to pay for AC. The tent pulls from the lung room when it’s too hot or too humid from a Vivosun fan with a controller. The humidifier bumps up the humidity in the tent off the inkbird where it needs to be. I also have a Vortex heater to keep the temp inside the tent where it needs to be. I used to use a inkbird temp controller for that but the new heater has a thermostat.
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I keep making the same mistake of cranking my lights, burning my plants turning them down for the next grow, things go great, so I try to turn them up again, and on and on lol
I try to keep my VPD optimal, but sometimes it’s all I can do to keep the humidity low enough to ensure I won’t develop bud rot or other pathogens.
I just run it as close as I can depending on what my outside influence of the lung room is. I use a Vivosun fan which can be set at 1 to ten. I just played with that until I got my numbers stable. Which is 1 for veg. Preferably around 78 for temp and 70 for humidity. This is only to pull air into the tent for lower humidity and temp. The inkbird turns the humidifier on when the tent humidity drops too low. My lung room is usually around 60 (the garage) and I keep the humidity below 60.
For the light intensity you just start out low and build up until you see negative results. I’ve noticed better quality definitely comes from not pushing the plant too hard with too much light. Once you start to push plants more light or CO2 you definitely have to adjust temp, nutrients, ect. things get more tricky. I don’t push mine hard or use CO2.
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Just being able to maintain something close to optimal VPD would have been huge for me, but the fogger allowed me to totally control it. I saw a 20% increase in yield the first grow using it. 
My grow room is in a daylight basement/garage. Right now there is a small window AC directly in the room. I’m in the process of converting the basement/garage into a lung room so it can also be used for maintaining the environments of a dry room and seedling room, which I currently don’t have a lot of control in. The AC is moving to the basement/garage along with all exhaust from all the rooms after passing through a filter. I only need the AC during the summer, but it definitely won’t work hard. The warmest I ever see it is maybe 75 to 80. In the winter AC will most likely always be off and it stays between 60 to 65.
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Yeah I built a cheap box with furnace filters from Home Depot to filter the air before it goes into the tent. This is the humidifier I use.
Kubicle Vornado Whole Room Evaporative Vortex Humidifier with Intelligent Automatic Humidity Control Air Refreshener Bundle Included
What do you use? It would be ideal to be able to use something with a bigger tank I wouldn’t have to fill up as often. This will last at least 5 days for me, which is ok.
I have a 45 gallon tote with a House of Hydro 12 Head Mist Maker Kit paired with an Inkbird humidity controller.
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That looks ideal! What did that cost to make? Minus the inkbird. I have that. I used to have the same heater lol. I like those more. I just don’t have the room for it.
Yep, it’s frickin ridiculous but it works unbelievably well.
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Yeah that’s super cool. I just need more room. I’m assuming I could make a small one with the 3 head fogger. What did you go with?
My room is 11 ft by 7 ft and 6 ft tall. It isn’t the most air tight area. I went with the 12 heads. I agree you could probably use the 3 head with a 5 gallon bucket.
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