So i have a question, if anyone is will tp help id greatly appreciate it. Im 5 weeks into flower and been read about vpd. I reat that in flower its best to keep vpd around .8 to 1.0 . In my tent 4x8x6 , i know my fans intake and exhaust aren’t perfect but they have worked thus far. My question is how would one maintain vpd during flowering with lights on. My vpd is around 1.8 which i hear is bad. Should i run a humidifier in tent during flower.? Please help , really trying to maximize my grows. My exhaust fan is at 195 cfm i have intake ac infinity t4 at setting 3. So i do have some negative pressure. Any thoughts or suggestions would be greatly appreciated.
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Ive poured a ton of money trying to get the perfect vpd and even though i can hit it in the winter, the summer i just cant with lights on. Lights off? Not that hard… but when its 93 outside and youre in a metal building, mother nature will always win 
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I was thinking that had alot to do with it. The hotter my house gets the worst vpd is. Getting into the 90s now.
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Yea man, i just get as close as i can and let it ride. Youll still produce big buds as long as the lighting and temps are efficient.
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Mind is i ask another question. I know no two plants grow the same but what would cause 2 plants to grow bigger then the 2 middle plant. Im guess better light reflection on ends of tent vs middle. Im only using 2 ts 600 and 2 sp 1000. Led lights.
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Usually the footprint of your lights should overlap and cover your plants equally, there not really an answer for that. It could be anything from phenos to nutrient uptake, ect. Thats why i like to LST and grow everything uniform.
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Yeah im just know learning how to lst properly lol. I have done i know 30 plants so far . And my buddy asked me why i still have a main stem at the end. I have only be training the bud branches. Sometimes i got lucky and was able to stop the main stem by training highest branches but it was was give intake lol.
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Its a challenge this time of year regardless. Im sure you know this but one 4inch exhaust is no where near enough air movement for a 4x8. I find it best to start the ladies in august and set to flower in oct for best conditions. A mini split would make everything perfect, but at a added cost. Personally i cannot justify it hear bc oz’s are 100 bucks here. Not really worth all the extra energy. But i make my one run a yr enough for yrs each time lol.
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Vpd is great and if its dialed in it really does accelerate growth. It pretty easy to do in veg but not so easy in flower if you got lots of big buds going…
Long story short is, you will drive yourself crazy trying to keep vpd in flower or risk mold.
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Yeah ill pass lol , definitely dont want mold
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Its less risky with cooler temps. Higher temps and vpd are def dangerous. I rather be below 50% rh regardless of vpd by wk 5 of flower
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@Poseidon1 i agree… i pushed these a little too hard. I wasnt expecting temps to sky rocket and even with a AC… 4 lights in the flower room with 11 plants… lights on best i can get it 81 until the lows outside get below 70 consistently for a few hours then i can hit high 70s for a few hours. Humidity is killing me but i have enough airflow to keep the mild out. Im done growing during the summer after this year. Its costing way too damn much.
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Have a very large budget or be in a friendly climate. As long as you’re not too far out on either side of VPD you’re going to do fine.
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A good flower VPD is 1.2-1.6 but it’s not just the VPD numbers that matter it’s what makes up that number. What are your temps and humidity?
A good place to be would be 80 degrees 55% that’s around a 1.5.
You don’t need to chase your tail trying to get it perfect, just understanding what VPD does and how it effects plants growth is important, I would suggest doing some reading on it and you will understand the “acceptable range”
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Yes. A humidifier should help. I run an AC Infinity humidifier (the humidifier itself is outside the tent), and run the hose in through one of the openings. I can get my VPD anywhere I need it, by keeping my lung room humidity lower, and adding whatever I need via the humidifier.
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I would concentrate on the basics rather than spending time and money chasing VPD. Yes, you can create an ideal VPD that will help some, but the additional gains are marginal at best. I simply maintain RH > 50% in veg and <50% in flowering and get results like this with good basics (proper pH, PPM, lighting, a good soil, proper watering, good nutrients,…):
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How do you not get mold during flowering. Lung room stays at 40 rh tent 45. If i pit a humidifier in lung room won’t dehumidifier suck up moist air. Cant put dehumidifier in tent temps get way to high and then vpd skyrockets.
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I have my lung room at ~40% I grow in a basement, and need to run a dehumidifier anyway, so I just set it for 40%). Then, I set my humidifier for VPD. In late flower I set it for a VPD of 1.6. I use my intake and exhaust fans to keep my temps around 80-81. My humidifier rarely comes on when set for 1.6, in this configuration. Earlier in the grow, I set my VPD for whatever my target is at that stage, and it adds humidity as needed.
EDIT for clarity:
Dehumidifier in lung room - set to 40
Humidifier beside tent, feeds in to tent (saves tent space)- set for target VPD.
Intake/Exhaust fans to manage temps. If needed can increase speed to lower humidity
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