Hello all, I have been reading threads on ilgm on Vpd. I’m in mid flower and they seem to be doing just fine so far. 4 autos, tent is at 78-81f and RH is 48%. My leaf temps are usually 3f higher than tent temp. I’ve been told to keep RH around 45 +- but Vpd is showing I should be 73f and leaf temps 73f. It’s not possible for me. I’d need an ac unit to keep temps down. I have a dehumidifier in the tent running which keeps heat up. Basically I’d need to be at 95f, leaf temps at 83f and RH@ 45 ish. It’s either lower temps and higher humidity or lower humidity and higher temps. But isn’t 40%RH where I need to be in midflower? How is everyone else keeping up?
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I wouldn’t pull your hair out trying to make it perfect, anything below 60 is fine for late flower with good air flow.
Edit. When I say good airflow I mean good circulation, above and below, Getting all corners.
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It’s definitely driving me crazy. I get like that. I immerse myself in this and it’s not working how I’d imagine! I’ll try to go a little higher on the RH and see how it goes. I do have 2 ac infinity fans (oscillating) each on a corner facing each other. Also one at the top facing down. Seems ok?… 3 of the 4 are defoliated pretty decent but the gg#4 is so damn bushy and their all small fan leaves. I don’t even know where to start. I start and 8 mins later I’m annoyed lol. Doesn’t even look like I did anything. But I know it’s important to get that crap out of there. You’ve helped me on another question and I definitely appreciate you.
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Unless you grow room or lung room has all the devices needed to do the following it is not worth the effort to track VSD. You will need to heat, cool with ac, a humidifier, dehumidification, and ventilation fans that can cycle by temperature and or humidity. Most of the the time it doesn’t make sense to try and put all of this in a tent, or to support one.
If you you do decide and try and maintain VSD insure all of your reading are accurate. I don’t really trust those point and shoot IR thermometers to be very close. Mine gives a four degree error on the leaves. You can use the attached chart to follow VSD closely or loosely.
As stated before the longer I grow, the more I just try and maintain above 50-55% during veg, and below 50-55 during flowering.
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I see. I do have all that stuff except stand-alone ac unit but I’m in a 4x4 tent in a basement laundry room. 0 ventilation out. 70f 55% RH. And accuracy is another issue I’m having. I have a controller that came with the in-line that works but always much different readings from the smart pro and the acu-rite. Even they are different. Have an ACI in-line with new controller so maybe that’s closer. Like @Autos-only mentioned not to fret too much. I gotta get more defoliating done so air can get in. Appreciate the insight.
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Best advice I can give you is don’t chase your tail trying to make it perfect. Do some reading and understand how and why VPD affects plants, nutrient uptake and gas exchange.
If my humidity is 60 or below I’m happy, I run a VPD between 1.2-1.4.
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Make sure that your temperature sensors are not in the direct light, and that they are shaded in some way. After I gave this advice to another member, and they reported a five degree reduction in the temperature reading after shading the sensor.
Also I would recommend taking the humidity reading in bottom section of the tent.
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What VPD target number/ range are you currently trying to hit?
With air temp at 80, leaf temp at 83, RH at 48%, your leaf VPD calculates out to 2.17kPa, which is a very high number/ transpiration rate. But are your leaves really transpiring at that rate? Higher leaf temp than air temp could indicate no, & that the stomata are actually closing up to retain moisture. Do you see a difference in the leaf temp offset if you check an hour after watering vs. right before you would water?Generally I want to see a negative offset rather than a positive offset ( Leaf Temp - Air Temp = Leaf Temperature Offset ) , but maybe you are intentionally watering to drought or something.
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I spent a long time and money trying to regulate vpd. I got tired of chasing it and throwing $$ at it. Mother Nature aint perfect and neither are my grows. As long as im satisfied then thats as close to perfect as ill get lol. We learn as we grow right?
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You could raise your humidity if you cannot lower your temps.
A range of 72-62% rh
Will bring you into range at your temp range.
I know you’d prefer a lower humidity… But without ac or lower temps…
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“Offset of -3.0” … if that is to be reporting the Leaf Temperature Offset, it should be +3f for that chart. I think you are going to confuse people by not labeling it as the “Leaf Temperature Offset”, & by not reporting the number as the answer to the equation “Leaf Temp - Air Temp = Leaf Temperature Offset” .
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It is a beta chart… The numbers i entered for math is what he listed.
The numbers(colored) on the chart are accurate… Which is the point to my answer. I did not use an offset… I used leaf temp. Notice the legend is off as well. If you followed my thread on this you’d see i am currently formatting and getting the vpd completed.
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That’s what I’m at right now. I didn’t know checking after a watering was a thing. Thats why I’m here. This is where I’m at
And this is what I was trying to achieve. Intentionally watering to drought? I’m not verse in the lingo I apologize.
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I’m starting to realize that… just want the ability to grow some sht like y’all got in your grow diaries.
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I thought about raising the humidity and actually started putting the humidifier in. But everything I read was +/- 40RH in flower so I bitc*ed out and went with the always on in-line and dehumidifier route. It’s getting closer. I’m just afraid to get bud rot and mold. I also opened the tent a little because the air in the basement is a little cooler. I appreciate your input I’ll take all the advice I can get.
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@Brian384 This has been a brutal summer for everyone, my basement usually is between 65-68f with the heat this summer… My basement is 72f minimum.
I have a 70 pint auto draining(with hose) dehumidifier in tge room my tents are in… My lung room.
I crank up my exhaust to suck air out brinibg in new cooler air.
I also have inline fans blowing cooler air in… You may need more than one.
I have two going right now. Best my temps have been now… 73-77f.
And about 40-50% humidity…
My lung room dehumidifier is set at 40-45 rh.
Due to forcing cooler air… It is messing witg my negative pressure a bit… So at times i mess what’s cooking in there… But it’s nit to bad.
You neg the side to suck in on the tent… Negative air pressure fir the charcoal filter to filter smells properly.
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My basement is usually freezing cold as well. Not this year. I have another in-line fan coming Tuesday so I may hook them both up and get some air moving. My dehumidifier is set to constantly on because it’s pulling in air that’s 55 or so plus the fabric pots im still hovering around 50. My negative pressure is sucking in the sides of the tent and my 2 oscillating fans are hitting the sides. Makes me nervous that they’ll fail. Had a cheaper one that now just blows straight down from the top of the tent because the oscillating arm inside broke from the tent.
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I believe in the KISS technique. I use both intake fan and exhaust fan with speed controllers. I adjust the speeds so that the tent has a slight negative pressure, and the side walls are just starting to pull in. This saves a ton of room in the tent. I can adjust both fans speeds up or down to change the amount of air flow through the tent. After this I just maintain the humidity level in the lung room for veg or flower.
The plants and some mediums will give off a lot of humidity. When I put a tent in the garage using coco the humidity stayed above 55%, even during the winter. I would have water collecting on the windows like there was a humidifier running. I use a dehumidifier this is OK during the cool weather, but it puts out heat. If I was growing in the summer I would use an AC unit.
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I think next grow which will be in fabric autopots I’ll have to rearrange the tent and fans I now have my in-line steady running at level 5 and now my temps are mid 70’s although the humidity is a bit higher at low 60s. I need some better temperature devices to actually see. They’re all different. Kinda getting annoying. I was going to put mine in the garage but it gets too hot and humid in the summer and too cold in the winter. I have a split unit but it’s probably too small for the garage.
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What kind if tent do you have?
You can by mounting bar or hi cfm bars… To help hold back the suck in.