VPD help needed

[HighLife]

4X4x8 tent
2 gorilla glue autos in mid flower
HLG Blackbird LED 600W
400 CFM

My temp is about 78, RH is 42 and VPD is 1.9. trying to get VPD down by raising humidity with small humidifier but none of my numbers are budging. Increasing exhaust fan isn't bringing temp down. My exhaust is outside the tent so it's pushing air in rather than pushing it out from within the tent. Would adding an exhaust to also push out air help this situation? Should I ignore VPD since temp and humidity are actually in good flowering range I think. ?? Maybe I need more powerful humidifier?

[golfnrl]

Environment is key, right? Keeping the temps and RH in range along with proper nutes will grow great weed with your setup. I try to chase the VPD occasionally, but I've noticed that keeping temps and RH in range seems to accomplish the same thing. I think you're good, others may have a different opinion.

[Bluey]

Do whatever you can you lower temps. Your RH is good, a bit better than mine with lights on. Aim for 24⁰C start of flower, 23⁰C mid and 22⁰C late flower.

The low temps will allow for exceptionally dense buds and low RH for increased potency.

[ZiroOne]

I'm not totally agree.

Although VPD greatly effects water use efficiency by plant but with proper watering frequency and correct nutrient solution EC and a little care it has no effect on yield or potency at least in the range of 1.0 to 3.0 kpa for sure. 'You can increase potency and yield by adjusting VPD/RH' is a lie charged by humidifier/dehumidifier manufacturers.

Yes. Temperature, greatly effecs yield and potency. Generally 20-30 C can be considered as optional temp. In this range yield goes up and potency goes down as temp increases. So if more yield is needed, it can be achieved by losing some potency with higher temp. Lower temp will result higher potency but lower yield. I prefer 28-32C with high light level and CO2 until last 2-3 weeks and then 18-22C. or 24-26 in the whole flowering phase when light level is not high.

[Ciccio]

https://vpdchart.com/

[Bluey]

The combination of higher temps, higher PPFD and supplemental CO² works well for increased yield, but most of us here don't use CO² because the increase in yields is not worth the cost of getting there.

Bud density and yield is directly related to temps in flower. It has been shown time and time again that temps closer to 20⁰C late in flower and at 24⁰C commencing flower produce higher yields than if the temps were higher, unless of course you are using CO² with increased light levels.

It has also been shown that lower RH produces higher THC levels than the same strain grown with higher RH in flower.

My own results here regarding yield and bud density confirms that lower temperatures do result in higher yields across all strains that I have grown to date.

Higher temps likely produces a faster growing and maturing plant IMHO.