Thoughts on VPD? I'm not sold on it.

nomaninsf

nomaninsf

Well-Known Member
I'm back into growing after a 10 year hiatus and have been researching new industry techniques and all anybody talks about now is VPD, but I'm not sold on it.

Anybody else having better results by ignoring VPD altogether and going with temps and humidity levels that are off the recommended "VPD Chart" spectrum?

I tried to chase VPD but found it to be counterproductive and was getting slow growth rates. As soon as I went back to my tried and true methods, and started ignoring VPD, my growth rates and overall plant health improved. I was going off the "Pulse" chart, which had veg pegged at a 0.9 to 1.1 VPD, but that was resulting in underwhelming growth rates and overall plant health for me. I switched to my preferred temps and humidity as a starting point, which hovers around 1.4 VPD on the chart, and all of a sudden my plants are thriving like I'm used to.

I'm interested to hear what other people think about VPD. VPD in my mind seems like marketing since every strain I've ever grown has different needs and can't be confined to a one-size-fits-all chart. I know there's science behind it, but I have a fully controlled environment and had my VPD on point (according to the Pulse chart) and the plants were not loving it. My current veg VPD is more aligned with the recommended flowering VPD numbers and is doing much better than the recommended veg VPD.
 
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ec121

Well-Known Member
nomaninsf said:
I'm back into growing after a 10 year hiatus and have been researching new industry techniques and all anybody talks about now is VPD, but I'm not sold on it.

Anybody else having better results by ignoring VPD altogether and going with temps and humidity levels that are off the recommended "VPD Chart" spectrum?

I tried to chase VPD but found it to be counterproductive and was getting slow growth rates. As soon as I went back to my tried and true methods, and started ignoring VPD, my growth rates and overall plant health improved. I was going off the "Pulse" chart, which had veg pegged at a 0.9 to 1.1 VPD, but that was resulting in underwhelming growth rates and overall plant health for me. I switched to my preferred temps and humidity as a starting point, which hovers around 1.4 VPD on the chart, and all of a sudden my plants are thriving like I'm used to.

I'm interested to hear what other people think about VPD. VPD in my mind seems like marketing since every strain I've ever grown has different needs and can't be confined to a one-size-fits-all chart. I know there's science behind it, but I have a fully controlled environment and had my VPD on point (according to the Pulse chart) and the plants were not loving it. My current veg VPD is more aligned with the recommended flowering VPD numbers and is doing much better than the recommended veg VPD.
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VPD is the difference between the amount of water vapor in the air and the air's saturation point, which is the maximum amount of water vapor the air can hold at its current temperature. That's scientific fact and you see proof of it when you see moisture on a lawn or your car when it hasn't rained.

All you need is a $5 hygrometer and a free chart on the internet to track VPD, so there's really nothing to market. If you spent $500 on a Pulse Pro, then the money was spent for all the automated data it measures in one unit and having all that data in one database with real-time monitoring, as opposed to buying multiple diagnostic tools and having to manually input all your measurements in an Excel file and having no real-time access.

So what you're really saying is that you disagree with botanists on their findings of the scientific effects VPD has on the growth and health of plants.

What is your preferred temp and rh?
 
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Phytoplankton

Well-Known Member
I think VPD is a decent guideline, stay “in the ballpark” and you’ll be fine, however, it’s only one piece of the growing puzzle. It might give you more growth, but, conversely, some of the best plants I’ve ever seen/smoked were grown outdoors, where there is no control of VPD,
 
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Delps8

Well-Known Member
nomaninsf said:
I'm back into growing after a 10 year hiatus and have been researching new industry techniques and all anybody talks about now is VPD, but I'm not sold on it.

Anybody else having better results by ignoring VPD altogether and going with temps and humidity levels that are off the recommended "VPD Chart" spectrum?

I tried to chase VPD but found it to be counterproductive and was getting slow growth rates. As soon as I went back to my tried and true methods, and started ignoring VPD, my growth rates and overall plant health improved. I was going off the "Pulse" chart, which had veg pegged at a 0.9 to 1.1 VPD, but that was resulting in underwhelming growth rates and overall plant health for me. I switched to my preferred temps and humidity as a starting point, which hovers around 1.4 VPD on the chart, and all of a sudden my plants are thriving like I'm used to.

I'm interested to hear what other people think about VPD. VPD in my mind seems like marketing since every strain I've ever grown has different needs and can't be confined to a one-size-fits-all chart. I know there's science behind it, but I have a fully controlled environment and had my VPD on point (according to the Pulse chart) and the plants were not loving it. My current veg VPD is more aligned with the recommended flowering VPD numbers and is doing much better than the recommended veg VPD.
Click to expand...
VPD is just a way of using one number to refer to different combinations of temperature and RH.

Overall, cannabis grows optimally, in veg at about 1.0, for example. The VPD chart tells you what combinations of temp and humidity will provide optimal growth for plants. If you're coming up with different numbers, it's not that VPD is "wrong". Instead it's an indicator that your grow environment is such that you're getting good results when your temperature and humidity values are quite different from "standard" values.

VPD is, at its core, a function of physics - if it's hot and/or dry, plants have to transpire more than when it's cool and/or moist. Transpiration is very important because water intake drives about 50% of nutrient uptake. Conversely, a lot of nutrient issues are resolved when VPD is brought back in range.

But if you're getting good results at 1.4 in veg, that indicates that something in your grow environment is allowing that to happen.

You might want to look into it or not but if you're consistently getting good results it might be easier just to take the win.
 

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