Not really, helps keep it up. My background Rh is say 75% 24/7/365 - at night not uncommon to get 90% in the tents/rooms.
I can choose my leaf offset. I have it on 0 - sensor is right there. In the leaves. Maybe I’ll take a baby thermometer but if its more then 1c difference I doubt it.
So under optimal conditions a leaf wants to be 2 degrees F lower than air temp. You are supposed to take a leaf temp reading and program the actual offset into this meter. If it's less than 2 degrees then the light is too close or turned up too bright.
VPD is even more vital if you use CO2. The wrong VPD can inhibit CO2 absorption.
You should research this a bit. As the manual says, correct VPD can bring a bigger yield than CO2.
What they mean is a non CO2 grow with proper VPD can give you a better yield than using CO2 at the wrong VPD levels.
VPD controls stomata, and stomata are the throttle for a plant. A plant is just a pump, and stomata regulate the speed that the pump can run at, so if it's wrong, more food or light or CO2 won't make them grow faster or bigger.
If the pump runs too fast it pulls in raw water without any nutes, and deficiencies start. If its running too slow you die of old age without growing as much as you could have.
You should be taking a leaf temp reading every day about 2 hours before lights out, and adjusting that offset accordingly, which will regulate your CO2 properly.
As light increases, your leaves work harder and warm up, just like people do when they exercise. So light is the driver behind leaf temp, not air temperatures.
A two degree difference is the perfect temp difference for maximum transpiration without causing harm.
The warmer air sucks water out of the plant. A two degree difference creates the perfect amount of suction, and the atmosphere drinks water from the ground through the plant like a straw, pulling nutes from the soil in with it.
The stomata are the restrictors in the straw. When VPD is correct, the stomata open up completely. Now CO2 can be absorbed properly.
VPD is physics, not biology, so it's a constant. It sets the stage for the grow. You set the VPD and the plant acts accordingly. Everything else is effected by VPD just as soil is effected by calcium.
If your air temp is 76, leaf temp 74, and RH is 48%, your VPD is 1.40.
If humidity plunges to 41%, you lower the room temp to 72, adjust the light to get a leaf temp of 70, and VPD is again 1.40.
The plant runs at the same speed under 2 very different climates just by monitoring VPD and adjusting.
It never missed a beat.
OK everyone, regardless of how you grow, if you don't understand VPD you should research it. If you are unfamiliar with it, then you are in for a really great treat. It's a game changer. Alot of problems disappear.
Overwatering is hard when a plant is moving water correctly, so that also fixes oxygen intake.
It steadies a grow.
My grow is a good example, it's a disaster. The light failed, then the replacement got turned up too high for a week, then I had to drench the pots because the 1st run soil mix was acting up, and I fried all the leaf tips to fix the soil but.... The buds are fantastic. Big, resineous, and stinky.
VPD is the only reason my crop survived. For everything that went wrong, a good environment carried them through so far, and if I stay on it I will have a splendid harvest.
If you are learning how to grow, its a basic skill you need, if you are an advanced grower, you are about to go up a full level.
those pictures had Canuk logo on them
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