Correct VPD in flower or lower humidity? Can't have both

[newleaf14]

When chasing VPD in flower you are dealing with humidity in the upper 60’s to low 70’s. That puts you in risk of PM. I do chase VPD and I also keep a lot of air movement and keep things defoliated. Does anyone else chase VPD or do you think it’s better to hold a humidity around 45%. Thanks everyone and I look forward to hearing how you all deal with this ( issue).
Happy smokin.

 

[Roy Growin]

Sorry to sound like a luddite, but I simply don't measure things and it doesn't bother me
Plants tell me if they are happy
I do keep a tab on temp/RH tho, so that would be my tuppence [neg]

 

[bluter]

vpd is a great information tool but i wouldn't bother chasing it. i've always been a believer in learning to grow through what the creator has given you for environment.

things can get expensive with humidifiers, dehumidifiers, etc following vpd. if you run co2 vpd becomes much more useful, otherwise it's not really a thing unless you are faced with an extreme native climate.

 

[newleaf14]

vpd is a great information tool but i wouldn't bother chasing it. i've always been a believer in learning to grow through what the creator has given you for environment.

things can get expensive with humidifiers, dehumidifiers, etc following vpd. if you run co2 vpd becomes much more useful, otherwise it's not really a thing unless you are faced with an extreme native climate.

Well I have to agree to disagree. Plants can’t breathe plants can’t grow. Not sure what you mean by the creator, can’t just grow indoors Willy nilly. lol. That’s how you lose your investment. Humidifier’s and equipment is something you need if you want quality that stands out. Environment is everything.

 

[Ke0ncp]

Well a higher VPD = lower RH. As you go up in VPD you are lowering RH by whatever means you can.

In my tent a VPD of 1.61 = a RH of 46.9%

I’m currently at a VPD of 1.25 and a RH of 59.5

I use 2 small room dehumidifier’s to try and keep humidity levels in check as best I can.

 

[Phytoplankton]

IMHO, I’d keep the rh down and not worry about the VPD, any additional growth the “perfect” VPD would give you will be eaten up by the pm and bud rot you’ll get from the higher rh.

Edit: VPD is a tool to consider, but I wouldn't live and die by it, it's just a small piece of the puzzle. Cannabis grows just fine outdoors where VPD swings drastically on a nearly daily basis, in all kinds of conditons, high temp/high RH, high temp/low rh, etc,

 

[newleaf14]

Well a higher VPD = lower RH. As you go up in VPD you are lowering RH by whatever means you can.

In my tent a VPD of 1.61 = a RH of 46.9%

I’m currently at a VPD of 1.25 and a RH of 59.5

I use 2 small room dehumidifier’s to try and keep humidity levels in check as best I can.

sounds like it’s tuned in pretty good.

 

[Makeminefullgrown]

Sorry to sound like a luddite, but I simply don't measure things and it doesn't bother me
Plants tell me if they are happy
I do keep a tab on temp/RH tho, so that would be my tuppence [neg]

You’re the only person, other than me, that has accurately used the word “Luddite”……how fascinating.
As for the VPD issue, I bring my mid to late flowering temps down to 76/77F and try for 50% rh. Although I know growers that run a higher RH in flower and don’t have problems. They do make sure they have really strong airflow, which is important regardless.

 

[Delps8]

When chasing VPD in flower you are dealing with humidity in the upper 60’s to low 70’s. That puts you in risk of PM. I do chase VPD and I also keep a lot of air movement and keep things defoliated. Does anyone else chase VPD or do you think it’s better to hold a humidity around 45%. Thanks everyone and I look forward to hearing how you all deal with this ( issue).
Happy smokin.

"When chasing VPD in flower you are dealing with humidity in the upper 60’s to low 70’s."
VPD is a way of using one number to express different combinations of temperature and RH. That's all it is. There's no magic and no mystery but it is different.

VPD is for plants what "feels like" is for humans.

"When chasing VPD in flower you are dealing with humidity in the upper 60’s to low 70’s."
This is not correct.

The recommended range for VPD for cannabis in flower is 1.2 to 1.4.
A VPD of 1.2 covers a range of temperature + RH combinations from 52°F and 0% Rh to 113°F and 82% RH.
A VPD of 1.4 includes temperature+Rh values ranging from 55° and 0% to 113° and 80%.

This is a screenshot of temperature and RH values that range from about 1.2 to 1.4, the range where cannabis will do well in flower. A VPD of 1.0 which is a little cool and/or moist for cannabis in flower and transpiration will slow. On the other hand, 79° and 42% is a little hot and/or dry so transpiration will go up and that means nutrient uptake is increased which could lead to nutrient issues.

 

[Delps8]

Sorry to sound like a luddite, but I simply don't measure things and it doesn't bother me
Plants tell me if they are happy
I do keep a tab on temp/RH tho, so that would be my tuppence [neg]

And since you keep watch on temp and RH, you're keeping watch on your VPD because VPD is just one number for a range of temp and humidity values.

My thruppence. ;-)

 

[bluter]

Well I have to agree to disagree. Plants can’t breathe plants can’t grow. Not sure what you mean by the creator, can’t just grow indoors Willy nilly. lol. That’s how you lose your investment. Humidifier’s and equipment is something you need if you want quality that stands out. Environment is everything.

haven't needed vpd growing over the last 30ish years and doubt it'd be of much value now.

doesn't bother me if folk use vpd as a tool. the best growers i know here just laugh at it, but they've been in the game decades for the most part. everyone kind of came up long before it was ever a thing. vpd is also heavily pushed by mfgrs that stand to gain by selling you the extra crap needed to chase it, so i take it under advisement.

again, it becomes much more useful if you run co2 or face an extreme native climate.

i time my indoor grows so they happen during the parts of the yr that is easy to control environment. everyone i know does the same. no one really grows in summer as a result unless there is an outdoor component.

whenever i've ever bothered to check my conditions against a chart i'm generally within the curve anyway. i also don't like that there are different vpd charts that can contradict each other. if you use one use a good source like the one @Delps8 follows.

 

[newleaf14]

And since you keep watch on temp and RH, you're keeping watch on your VPD because VPD is just one number for a range of temp and humidity values.

My thruppence. ;-)

It’s difficult to have 20 large plants in a 12x12 grow without controlling the environment. I would have water dripping off the ceiling and down the walls during lights off when the plants gas off. Couple plants in a tent with the door open ,, yeah I could see that.

 

[newleaf14]

It’s difficult to have 20 large plants in a 12x12 grow without controlling the environment. I would have water dripping off the ceiling and down the walls during lights off when the plants gas off. Couple plants in a tent with the door open ,, yeah I could see that.

It’s difficult to have 20 large plants in a 12x12 grow without controlling the environment. I would have water dripping off the ceiling and down the walls during lights off when the plants gas off. Couple plants in a tent with the door open ,, yeah I could see that.

Keeping an eye on VPD the resulting equation of temp and humidity that creates the best environment for the plants to breath. But if you didn’t know the importance I’m thinking we are in different galaxies.

 

[bluter]

It’s difficult to have 20 large plants in a 12x12 grow without controlling the environment. I would have water dripping off the ceiling and down the walls during lights off when the plants gas off. Couple plants in a tent with the door open ,, yeah I could see that.

it's about air movement. more than anything.

we ran over 200 plants in 3 8x8s, 2 6x8s, 2 2x2s, and couple miscellaneous seedling areas. we built air exchange from the growing areas into lung rooms, and then scrubbed the lung rooms and exhausted to outdoor.

it was a licensed med grow run for 10 yrs. we never once needed a vpd chart.

for what it's worth, worry more about bud rot and having your rh% too high. great vpd means nothing if the whole crop is tossed due to mold.

edit : if you are going to use it read up on what @Delps8 is doing and follow a couple of his grows.

 

[Delps8]

It’s difficult to have 20 large plants in a 12x12 grow without controlling the environment. I would have water dripping off the ceiling and down the walls during lights off when the plants gas off. Couple plants in a tent with the door open ,, yeah I could see that.

It may be difficult with 20 plants in a 12' area or it may not be difficult. It varies with the environmental conditions that exist in the area. If the climate is mild, you'll end up with an environment that's conducive to keeping temperatures and RH VPD in range. If it's not, it's up to the grower to control/influence the environmental conditions so that VPD values temperatures and RH are in range.

If you can't get temperatures and RH VPD values in range, plants won't grow at optimal rates.

The reason I keep doing strikethrough on "temperatures and RH" and "VPD" is to try to drive home the fact that they're just two different ways to define temperature and RH.

The fact that it's difficult to control the environment for 20 large plants in a 12' area has absolutely nothing to do with whether you're using VPD (one number) vs using temperature and RH (two numbers). If it's hard to keep temperature and RH in range it's because it's hard to keep temperature and RH in range.

And, sure, if everything else is equal, it takes fewer resources to keep VPD in range for two plants than it does for 20.

And that has absolutely nothing to do with any label you put on the amount of energy in the air or the amount of mosture in the air - temperature, relative humidity, VPD are just labels. The fact that it's harder to keep 144 square feet at a certain state than it is to keep 8 square feet at a certain state is of no consequence in a discussion of what labels to use.

Which is hotter - 20°C or 68°F? They're just different labels for the same level of energy.

VPD is as difficult as people want to make it to be.

 

[Delps8]

it's about air movement. more than anything.

we ran over 200 plants in 3 8x8s, 2 6x8s, 2 2x2s, and couple miscellaneous seedling areas. we built air exchange from the growing areas into lung rooms, and then scrubbed the lung rooms and exhausted to outdoor.

it was a licensed med grow run for 10 yrs. we never once needed a vpd chart.

for what it's worth, worry more about bud rot and having your rh% too high. great vpd means nothing if the whole crop is tossed due to mold.

edit : if you are going to use it read up on what @Delps8 is doing and follow a couple of his grows.

You chose not to use VPD and went by temperature and RH. That has nothing to do with the value of VPD because they're just different labels.

No one "needs" a to use VPD chart — it's just a handy way to discuss combinations of temperature and RH. There's no reason to not use ranges of temperature and RH because that's all that VPD is.

Per my other posting, it's as simple or as complex as people want to make it.