Let’s talk vpd

[Goodflower]

As the title says. Let’s discuss what your exp is with what you would consider an acceptable vapor pressure deficit. We’ve all seen the charts and what to shoot for as far as they go but what have you exp first hand. I live in a climate where humidity is a bitch! I am in my first legal commercial grow and am using a modified greenhouse structure. My build is by no way sealed and I must rely on exhaust fans as well as humidifiers to try and control and maintain what I would think is a good vpd. As a rule of thumb as a grower I’ve always tried to keep my humidity at 60 or less while in flower. As I’m studying vpd and what it means as well as battling my weather I’m finding I can still hit what is considered a good vpd with 70% or even a lil higher relative humidity as long as I keep the temps high. This goes against everything I’ve ever been taught so I’m here asking what you guys think or what have you seen personally. Is it really ok to flower with so much humidity as long as the heat is high enough to keep the vpd at the acceptable numbers? How likely is mold or bud rot? I have excellent air flow throughout the grow so it’s always moving.

 

[dank.frank]

VPD is for growing vegetation. I want to grow trichomes. Any temps over 78 degrees, indoors, will reduce trichome field density. Follow VPD during the first couple weeks of flower to increase growth rates and once stretch stops, I ignore it completely.



dank.Frank

 

[stiff]

don't forget,high humidity is no good for your filter.
At 75% humidity your charcoal filter is most likely gone or on its way out.
Time for an AC unit or dehumidifier when it comes close to it..at least in flower.

 

[dank.frank]

don't forget,high humidity is no good for your filter.
At 75% humidity your charcoal filter is most likely gone or on its way out.
Time for an AC unit or dehumidifier when it comes close to it..at least in flower.

100% accurate. Above 60-65% you will see a reduction in the lifespan and efficacy of carbon.



dank.Frank

 

[Goodflower]

I do not use any carbon filters. I’m in the middle of 250 acres with the closets neighbor being at least 2.5 miles away

 

[Goodflower]

100% accurate. Above 60-65% you will see a reduction in the lifespan and efficacy of carbon.



dan

VPD is for growing vegetation. I want to grow trichomes. Any temps over 78 degrees, indoors, will reduce trichome field density. Follow VPD during the first couple weeks of flower to increase growth rates and once stretch stops, I ignore it completely.



dank.Frank

Ok but what would be your view as far as using vpd to calculate where you needed to be to avoid mold when your in a climate that has super high ass humidity and you can’t really use any more dehus. I have two 5 ton package units on a 2k square foot greenhouse. I can control the temps but the humidity fluctuates so much outside daily that it’s a constant battle

 

[Switcher56]

Ok but what would be your view as far as using vpd to calculate where you needed to be to avoid mold when your in a climate that has super high ass humidity and you can’t really use any more dehus. I have two 5 ton package units on a 2k square foot greenhouse. I can control the temps but the humidity fluctuates so much outside daily that it’s a constant battle

I remember my 1st run, shit I could even grow tomato plants LOL. Someone mentioned VPD. Never heard the word or understood its meaning. Found a video on the tube, this was not cannabis related but, his grow look like my tomato plants which I wanted to give a head start. I moved the plants to a southern window until it was time to plant them outside. The entire run was timed to coincide (tomatoes then cannabis).

Because of the large fluctuations in heat and RH of the Maritimes (to hard to control mother nature) I only do 2 runs a year. I end my winter run around the end of May and forgo growing until the end of Aug.

The short strokes is it is a guide of where you should be, a target. This is the chart I use. Why? It takes the guess work out of it. e.g where you should be at the various stages. FWIW, I bloom at 75/55. Works for me in "my" environment. YMMV

When one is growing indoors, one becomes the environment. My settings and controller(s) setup are set in such a fashion, to prevent constant tweaking, and that my friend is golden

 

[revegeta666]

I also follow a chart and adjust the temperature of the room to fit the chart, but then I was told you are supposed to measure the leaf surface temperature with one of those pistol thermometers, because vpd relates to transpiration. What's up with that?

I also ignore it after week 3-4 of flower because of the risks high humidity brings. Following the chart during the veg phase seems to put your plants in turbo mode haha

 

[[Maschinenhaus]]

Stomata

The stomata in the leaves absorb CO2 during photosynthesis and release water vapor and oxygen into the environment. When humidity is too low, the stomata close to prevent the plant from releasing more water vapor than it can absorb as cell pressure drops. This also reduces photosynthetic efficiency and, correspondingly, the formation of assimilates.

Low evaporation over a long period of time thus leads to poor nutrient supply in the plant. For this reason, the stomata in greenhouse cultures should, if possible, always be open - even at night - so that they can evaporate. The value of humidity depends on the temperature. The higher the temperature, the more water the air can absorb.

High VPD usually causes plants to close their stomata to minimize water loss and avoid embolism in the water conducting vessels (cavitation). This occurs at the expense of reduced carbon uptake by photosynthesis. At the same time, transpiration increases up to a certain threshold, beyond which it remains high or begins to decrease. This can further increase the water stress of the plants.

The table is a good guide, I pay attention to three parameters from the flowering stage, temperature, soil and air humidity.

With the table you do nothing wrong.

Compendium: Earth-Water-Light-Microorganisms-Ion-Exchange-Nutrients

Chapter 8 Indoor cannabis cultivation - Many problems? Many problems can be prevented in advance, good gardeners know it, less is more! Interactions between nutrients - causes of malnutrition. Causes of nutrient deficiencies are inharmonious nutrient ratios in the soil, in addition to...

www.icmag.com

 

[Bio boy]

I remember my 1st run, shit I could even grow tomato plants LOL. Someone mentioned VPD. Never heard the word or understood its meaning. Found a video on the tube, this was not cannabis related but, his grow look like my tomato plants which I wanted to give a head start. I moved the plants to a southern window until it was time to plant them outside. The entire run was timed to coincide (tomatoes then cannabis).

Because of the large fluctuations in heat and RH of the Maritimes (to hard to control mother nature) I only do 2 runs a year. I end my winter run around the end of May and forgo growing until the end of Aug.

The short strokes is it is a guide of where you should be, a target. This is the chart I use. Why? It takes the guess work out of it. e.g where you should be at the various stages. FWIW, I bloom at 75/55. Works for me in "my" environment. YMMV
View attachment 18785127
When one is growing indoors, one becomes the environment. My settings and controller(s) setup are set in such a fashion, to prevent constant tweaking, and that my friend is golden

Without the dreaded mg ca deficiency ? What leds are you using btw switcher ?
I’m h l g and 73f 55rh and mg all over and I’m told I need to up temps to 80 to fix the mg in soil due to lack of infra red

 

[Switcher56]

Without the dreaded mg ca deficiency ? What leds are you using btw switcher ?
I’m h l g and 73f 55rh and mg all over and I’m told I need to up temps to 80 to fix the mg in soil due to lack of infra red

Meizhi 300W veg, 600W bloom.