Aqua Man said:

VPD is both temp and humidity. I agree temps are a huge huge factor. Thats the first thing I get right... next is the humidity and I do that using VPD. First I get my leaf temos where I want then adjust the humidity to match VPD.

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The point is that while you do all that and get 2 gpw other growers dont and also get 2gpw.

But the same can not be said if one grower grows at a colder temp than the other. That slows down growth.

I have read all about vpd in articles and threads. Still not one smidge of actual evidence it matters.

It would matter if you had a hot and very dry greenhouse in say colorado. Hot and dry can be disaster to crops. So they add humidity to lessen the impact. I believe the vpd chart came from that.

It is not mentioned in any greenhouse or gardening guide i have read though. I have only seen it mentioned regarding weed growing.

But i have not searched for this stuff in a while.