VPD and outdoor growing? Does it matter?

[sp838]

Hello all, was just wondering, since VPD seems to be of utmost importance, how can it be managed when growing outdoors? Or is it only an issue for indoor growing? Not sure why that would be the case though....

Currently in my neck of the woods temps and humidity are already out of range for ideal VPD. Humidity maxing out at 40% with temps above 75°, that's barely the right VPD for veg. Way too high for seedlings. RH in the 30s and temps above 75 and we're in the danger zone, that's technically already too high for flowering even.

So, how do we do it? Or does it somehow not matter outside? Would like to know everyone's thoughts.

 

[Oldchucky]

Don’t think you can do much to control it. More about controlling the root zone and reacting to what the plants are telling you. Just my two cents.

 

[BigBlonde]

... is it only an issue for indoor growing?

Yes. It is.

We control the plant's climate when growing in a tent. That's a good thing, but it's also a challenge. The fact that climate control can be difficult is why we focus on it so much. We also like to optimize our yield, and climate control is a significant part of that pursuit.

 

[sp838]

Why though? Why is an outdoor plant ok whereas indoors it's not, when both have the same VPD?

Currently where I live the temperature is 72° at 30% rh. This is a VPD of 1.7 According to the chart this would be way too dry for veg, let alone seedlings. So how is it ok for outdoor plants? According to the chart at 72° we want a max of 1.2 for veg, and only .8 for seedlings. So why is it ok for outdoor plants to have such high VPD? What's the difference?

 

[Oldchucky]

Probably the same reason you will be a lot healthier doing a lot of hiking outdoors compared to a guy doing a 10 year stretch in San Quintin! Sunlight, fresh air, lot, larger plants, and root volume. And it doesn’t really matter why. It just is. Plants are adaptable.

 

[BigBlonde]

Why is an outdoor plant ok whereas indoors it's not, when both have the same VPD?

I'm not sure it is okay in every case. Sometimes outside crops fail.

All plants evolved in the natural environment, not tents. I read once that plants must be highly adaptable because they don't have the ability to be mobile like animals do. I see that when I grow them. They can survive surprisingly well in inhospitable circumstances. They can be conditioned to live in environments that are foreign to their evolution.

 

[Oldchucky]

Yeah, they started out outdoors and adapted through evolution. Then we’re moved indoors and parameters had to be concocted to achieve the best results.

 

[sp838]

To me it seems like the VPD chart is actually an optimization that allows indoor growers to grow weed under better conditions than outdoors. The plant is resilient and adaptable but maybe two identical plants, one growing outdoors vs one indoors, the indoor plant can outperform the outdoor one if the VPD and temps are kept in ideal ranges vs the outdoor one that has to deal with swings in environmental factors...

 

[BigBlonde]

To me it seems like the VPD chart is actually an optimization that allows indoor growers to grow weed under better conditions than outdoors. The plant is resilient and adaptable but maybe two identical plants, one growing outdoors vs one indoors, the indoor plant can outperform the outdoor one if the VPD and temps are kept in ideal ranges vs the outdoor one that has to deal with swings in environmental factors...

I agree.

I've come to think of the VPD chart as a guide. In my experience so far, reading the plants seems to matter most. Just watering them changes the VPD on the controller, but the plants do okay. At times, I wonder how much the plants themselves can affect the environment in the tent.