VPD

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Username85

Well-Known Member
So I didn’t even know what VPD was until a few days ago and I wanted to get some input about my numbers. I’m adding the VPD chart I’ve been basing my numbers on. For the most part it’s within the “green” range, but I have to run a heater/humidifier and numbers fluctuate after the heater clicks off.
I circled the “problem” VPD range, 76°/55%. Are these kind of numbers something to worry about, or am I going down a rabbit hole here?
 

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Username85

Well-Known Member
insomnia65 said:
I don't think so, it's adding to your knowledge and this knowledge is needed for you to grow your ladies better. Do keep watching out for rabbit holes though, Ive been down loads and still haven't found Alice.
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I agree about gaining the new knowledge, still a long way to go. Do you think my range will be detrimental to the plants?
 
Arkos

Arkos

Well-Known Member
For small plants like that yes the vpd is too high, pun intended :eyesmoke:

vpdchart.com I like to use this chart as it tells you where in the grow cycle you want your vpd, probably all of them do I just find this one easy to read.

A infrared thermometer is a good addition to your vpd arsenal.
 
Roy O'Bannon

Roy O'Bannon

Well-Known Member
Vpd, leaf temp with new cooler led's with no infrared heating the leaves.. idk how to run that. My leaf temps match my air temps it seems.
If I go over 80f I can't keep the humidity down so...
 
insomnia65

insomnia65

Well-Known Member
Arkos said:
For small plants like that yes the vpd is too high, pun intended :eyesmoke:

vpdchart.com I like to use this chart as it tells you where in the grow cycle you want your vpd, probably all of them do I just find this one easy to read.

A infrared thermometer is a good addition to your vpd arsenal.
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That is an amazing.tool, thank you very much.
 
U

Username85

Well-Known Member
Arkos said:
For small plants like that yes the vpd is too high, pun intended :eyesmoke:

vpdchart.com I like to use this chart as it tells you where in the grow cycle you want your vpd, probably all of them do I just find this one easy to read.

A infrared thermometer is a good addition to your vpd arsenal.
Click to expand...
Wow, thank you for that link, I’m finding it much easier to understand after looking at that lol.
Seems my next step is going to be getting the thermometer. Seems like it would be really difficult/impossible to say a VPD accurately without leaf temp in the equation.
 
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Username85

Well-Known Member
insomnia65 said:
Think you need to up your RH a bit.

The chart web page is brilliant.
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Yeah that’s the one area that’s been hard to stabilize. After my heater turns off it drags down the RH quite quickly, and I have my humidifier running full power. Might just have to upgrade my humidifier if the warmer weather doesn’t help stabilize.
 
Arkos

Arkos

Well-Known Member
Good humidifier and dehumidifier is a very good investment along with a heater/cooler and control of those devices.
Inkbird controller's work fine if budget is tight.

Forget about those home/office humidifiers, they can't keep up with air extraction, the reservoir are to small and they can be a fire hazard from my experience.

Imo environment is the most important part to get right with this hobby :eyesmoke:
 
insomnia65

insomnia65

Well-Known Member
Arkos said:
Good humidifier and dehumidifier is a very good investment along with a heater/cooler and control of those devices.
Inkbird controller's work fine if budget is tight.

Forget about those home/office humidifiers, they can't keep up with air extraction, the reservoir are to small and they can be a fire hazard from my experience.

Imo environment is the most important part to get right with this hobby :eyesmoke:
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Any suggestions on what humidifier, we all want cheap to run and not so expensive, but I will settle for a cheap to run one that will last ofc.
 
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1212ham

Well-Known Member
Username85 said:
Yeah that’s the one area that’s been hard to stabilize. After my heater turns off it drags down the RH quite quickly, and I have my humidifier running full power. Might just have to upgrade my humidifier if the warmer weather doesn’t help stabilize.
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That's odd, humidity should rise as temp drops. Anyway, reduce airflow through the tent to increase temp and humidity. The plants will transpire more and raise humidity as they get larger.

Around 28C/82F is best air temp with LED since transpiration normally cools leaf temp to 1-2C under air temp. With HID leaf temp is higher due to IR heating the leaves.
 
Arkos

Arkos

Well-Known Member
insomnia65 said:
Any suggestions on what humidifier, we all want cheap to run and not so expensive, but I will settle for a cheap to run one that will last ofc.
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If you're in the States you have options, generally speaking a centrifugal or ultra sonic is going to consume low power, maintain the humidity at correct levels and probably not burn your house down. Those greenhouse grade ones are definitely overkill for smaller/mid sized tents but it's always good to have a bigger reservoir than 1gal...

I'm in Europe and using Hr-15 which seems to be a generic humidifier that everyone likes to slap their name on, ideal air have it in the states.
www.ideal-air.com

Ideal-Air™ Commercial Grade Humidifier 75 Pints | Ideal Air

This excellent quality humidifier features a multi-directional fogging head. The coverage is from 160–320 sq ft, depending on humidification requirements and ceiling height. Maximum output is 75 pints per day. Commercial-grade motor for years of use. Connects directly to your water supply with...
www.ideal-air.com www.ideal-air.com

I'm sorry I can't be of more help than that but I'm sure you'll find something to suit your setup.
 
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Username85

Well-Known Member
insomnia65 said:
Mine have been too low, great for flower bad for Veg I put a wet towel in there for now need a humidifier
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Yeah my humidity hovers around 43-
1212ham said:
That's odd, humidity should rise as temp drops. Anyway, reduce airflow through the tent to increase temp and humidity. The plants will transpire more and raise humidity as they get larger.

Around 28C/82F is best air temp with LED since transpiration normally cools leaf temp to 1-2C under air temp. With HID leaf temp is higher due to IR heating the leaves.
Click to expand...
yeah I thought it was odd too lol. The room my tent is in has a stable humidity of around 40~50, ive got two small fans (6”) feeding air into the tent, an oscillating fan & fan for top of canopy, with a 6” inline ducted out to carbon filter. To keep my temp up in the tent I’m running a small space heater (4min on, 9 min off) with the humidifier going full power. When the heater is on temp gets to around 77~79 with a humidity around 60. With the heater off for 4 min it drops to 76/57 range and when it’s been off for 9 min it gets to around 74/59.
I’ve been adjusting and monitoring these numbers for days and I haven’t dialed it in lol.
I only have a 1L humidifier, basically one you stick on a desk for an office, pretty certain I need to upgrade the humidifier
 
U

Username85

Well-Known Member
Arkos said:
Good humidifier and dehumidifier is a very good investment along with a heater/cooler and control of those devices.
Inkbird controller's work fine if budget is tight.

Forget about those home/office humidifiers, they can't keep up with air extraction, the reservoir are to small and they can be a fire hazard from my experience.

Imo environment is the most important part to get right with this hobby :eyesmoke:
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Do you think something like this is even worth the purchase?
I looked into the HR15 you mentioned and that’s just way out of my budget for the time being. This one says it can handle a room up to 720 sq ft and holds 6L and has filters to purify the mist.
 

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RadicalRoss

Well-Known Member
Arkos said:
For small plants like that yes the vpd is too high, pun intended :eyesmoke:

vpdchart.com I like to use this chart as it tells you where in the grow cycle you want your vpd, probably all of them do I just find this one easy to read.

A infrared thermometer is a good addition to your vpd arsenal.
Click to expand...
Wow that vpdchart.com rocks. I'm actually looking at some random points in my last, troubled grow and it turns out my vpd was way off. I'm well into the red zone for much of my grow. Among other changes to my growing technique for this tent, I'll be using vpd to determine my target temp / humidity.
 
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