Trust this chart?

[Dinger]

I was given this chart today from another member on the forum.

As I'm looking through the chart I find it very interesting that depending on the temperature and humidity there are the different zones to grow in. I've always been told for flowering prevent Bud rot or mold you wanted to be the lowest humidity you can get it. If I read the chart correctly I can keep temp at 75 with a 55% humidity and not get any mold, am I reading that right

 

[thebigearl]

I'm flowering in the 60's % no issues.
18c-23c temps

 

[thebigearl]

Just be sure you have good air movement of course.

 

[Herby Paisley]

Just be sure you have good air movement of course.

The Big earl is right its all about the air flow! ... keep it breezy

 

[Nunyabiz]

According to that chart even up to 80% humidity at 75 degrees. That might be pushing the envelope though.
I usually run my VPD at 79 to 82 degrees with humidity at 65 to 70% seedling and veg then after about 1st week of flower I start dropping the humidity by 5% every week so by the last week of flower iam 30-35% to stress the plant a bit to squeak out a few more trichomes. And I try to lower my temp in flower also, preferably about 75 degrees which is tough in the summer.

 

[Barney86]

Yeah those charts are good mate. Best to stick to the lower end for bloom though.
The difference is night and day when you can keep the vpd on point.
Once you get it dialed in you get massively better growth rates and bigger buds. They even smell a lot stronger.
Don't have to worry about going out of range like. It's not drastically important to be exact but your crop will thank you for it.

 

[Dinger]

Yeah those charts are good mate. Best to stick to the lower end for bloom though.
The difference is night and day when you can keep the vpd on point.
Once you get it dialed in you get massively better growth rates and bigger buds. They even smell a lot stronger.
Don't have to worry about going out of range like. It's not drastically important to be exact but your crop will thank you for it.

What do you mean lower end?

 

[Bush Doctor 77]

My greenhouse has been +32C and around 20-35% RH for over a month during the daytime. I haven't seen any signs of stress, and actually they took off during the hot weather. Those charts may be correct for leaf surface microclime, but not ambient air from what I'm seeing. I do circulate the air well, and have an 18" exhaust fan.

Some of the best I've smoked in 50+ years was grown in the Sandia Mountains, New Mexico @ 7000'+, high southern desert(35 degrees N). Extremely warm days, cold nights and no humidity to speak of.

 

[TurboBucket]

As far as I know to actually calculate vpd requires the leaf surface temp. The relationship between ambient temp and Rh compared to the leaf stomata temp and Rh. So different leaf temperature differences require a different chart. That chart doesn't seem to take leaf surface temperature into account at all.

 

[Barney86]

What do you mean lower end?

Sorry mate, meant keep the humidity on the lower end for bloom and keep the temp relative to that.

 

[Barney86]

My greenhouse has been +32C and around 20-35% RH for over a month during the daytime. I haven't seen any signs of stress, and actually they took off during the hot weather. Those charts may be correct for leaf surface microclime, but not ambient air from what I'm seeing. I do circulate the air well, and have an 18" exhaust fan.

Some of the best I've smoked in 50+ years was grown in the Sandia Mountains, New Mexico @ 7000'+, high southern desert(35 degrees N). Extremely warm days, cold nights and no humidity to speak of.

I'm a hot grower too mate. I like my room early 30s and my res at 25-27*c once the plants are established.
As long as I watch the light distance my plants love it.
I done a few vpd precise grows when I started in tents though and It really does make a difference. I can't hit the yield numbers without a tent to help me control everything. Just an open attic now cos a tents just not plausible at the moment.

 

[bobrown14]

As far as I know to actually calculate vpd requires the leaf surface temp. The relationship between ambient temp and Rh compared to the leaf stomata temp and Rh. So different leaf temperature differences require a different chart. That chart doesn't seem to take leaf surface temperature into account at all.

This ^^^ the chart should be used as a "guideline"

Plants have the ability to make their own micro-climate at each leaf surface by bending turning either toward the light or toward the breeze or partway in between and the plants do it for different reasons at different times.

Get in the ball park, keep the fans blowing, the water flowing and the lights lighting.

It's a weed.

The most important takeaway for me and VPD is that its real important that the plant is able to transpire and do it efficiently.

I've been growing in +32C and humidity from 60-95% RH consistently for 3 months. Some plants can handle the stress better than others. Its genetics mainly.

 

[SQl2kGuy]

I was given this chart today from another member on the forum.

As I'm looking through the chart I find it very interesting that depending on the temperature and humidity there are the different zones to grow in. I've always been told for flowering prevent Bud rot or mold you wanted to be the lowest humidity you can get it. If I read the chart correctly I can keep temp at 75 with a 55% humidity and not get any mold, am I reading that right

Hey @Dinger ... I'm using this chart ...

​

So ... RH 55% is probably the highest you want to go in flower ... any higher and you run the risk of mould.

But with mould there has to be a few factors present ... not just RH.

You could bring the temp up ... or even leave the temp the same 24°C (75°F) and drop the RH to 45%. This would be my first choice.

 

[Dinger]

This ^^^ the chart should be used as a "guideline"

Plants have the ability to make their own micro-climate at each leaf surface by bending turning either toward the light or toward the breeze or partway in between and the plants do it for different reasons at different times.

Get in the ball park, keep the fans blowing, the water flowing and the lights lighting.

It's a weed.

The most important takeaway for me and VPD is that its real important that the plant is able to transpire and do it efficiently.

I've been growing in +32C and humidity from 60-95% RH consistently for 3 months. Some plants can handle the stress better than others. Its genetics mainly.

I guess it is the uncertainty of the first grow for newcomers that cause all the questions. I ask a ton!

 

[SQl2kGuy]

I'm flowering in the 60's % no issues.
18c-23c temps

Hey @thebigearl ... I'm glad you have no issues.

You could likely drop the RH a bit and be safer with better growth rate.

Here's a good article from our Sponsor ... if you're interested ... Indoor Cannabis Growing: Relative Humidity and Temperatures

 

[SQl2kGuy]

According to that chart even up to 80% humidity at 75 degrees. That might be pushing the envelope though.
I usually run my VPD at 79 to 82 degrees with humidity at 65 to 70% seedling and veg then after about 1st week of flower I start dropping the humidity by 5% every week so by the last week of flower iam 30-35% to stress the plant a bit to squeak out a few more trichomes. And I try to lower my temp in flower also, preferably about 75 degrees which is tough in the summer.

Hey @Nunyabiz ...

Those are excellent ranges!

Right now I am increasing the RH a bit and decreasing the temp a bit for my VPD.

I agree ... it's a bit more challenging in the summer ... and also because I run my exhaust fan non-stop ... 24-0.

 

[SQl2kGuy]

My greenhouse has been +32C and around 20-35% RH for over a month during the daytime. I haven't seen any signs of stress, and actually they took off during the hot weather. Those charts may be correct for leaf surface microclime, but not ambient air from what I'm seeing. I do circulate the air well, and have an 18" exhaust fan.

Some of the best I've smoked in 50+ years was grown in the Sandia Mountains, New Mexico @ 7000'+, high southern desert(35 degrees N). Extremely warm days, cold nights and no humidity to speak of.

That's really interesting @Bush Doctor 77 ... I would have thought in that range the plants would slow down a bit.

I know leaf temperature comes into play and it can differ from 2°C (4°F) to 6°C (12°F) from ambient air temp.

I wonder if these charts can apply to outdoor grows? I'm curious now, so I'll try to find an answer to that.

 

[SQl2kGuy]

As far as I know to actually calculate vpd requires the leaf surface temp. The relationship between ambient temp and Rh compared to the leaf stomata temp and Rh. So different leaf temperature differences require a different chart. That chart doesn't seem to take leaf surface temperature into account at all.

Excellent point @TurboBucket ... the chart I have points to that saying ... "VPD when leaves are 2°C (4°F) cooler than air temperature"

 

[SQl2kGuy]

I'm a hot grower too mate. I like my room early 30s and my res at 25-27*c once the plants are established.
As long as I watch the light distance my plants love it.
I done a few vpd precise grows when I started in tents though and It really does make a difference. I can't hit the yield numbers without a tent to help me control everything. Just an open attic now cos a tents just not plausible at the moment.

Thanks for that feedback @Barney86 ... I have been researching this for a few weeks and hadn't run into anyone here who had actually tried it.

It's good to know I am going in the right direction!

 

[SQl2kGuy]

This ^^^ the chart should be used as a "guideline"

Plants have the ability to make their own micro-climate at each leaf surface by bending turning either toward the light or toward the breeze or partway in between and the plants do it for different reasons at different times.

Get in the ball park, keep the fans blowing, the water flowing and the lights lighting.

It's a weed.

The most important takeaway for me and VPD is that its real important that the plant is able to transpire and do it efficiently.

I've been growing in +32C and humidity from 60-95% RH consistently for 3 months. Some plants can handle the stress better than others. Its genetics mainly.

Good advice @bobrown14 ... I agree ... I am using it as a guideline to get into the ballpark ... while constantly keeping a close eye on the plants.