VPD with unknown Strains

[Mastermind23]

What is your VPD to go with an unknown strain from seed to harvest ?
When do you adjust your VPD due the different stages of your cultivar ?
Especially on interest, when does "Late Veg" start for you?
Do you have better experience with a fixed VPD or you let it within a range ?



Something you really have to keep in mind:

As the Leaf temperature is about 2°C colder than the air temperature on average when LEDs are on and nearly about the same or slightly cooler when the lights are off, you need to make adjustments to maintain within the optimal VPD range.

E.G. If your leaf temperature is 2°C cooler than the air and you are aiming fo 1kPa VPD daytime with LEDs on you are setting your automation to 24°C and 55%rH or 26°C and 59% rH or 30°C and 66%rH The Result is in all examples the same VPD of ~1kPa.

If your lights go off and your temperature is going down to 20°C, you need to keep in mind that your leaf temperature is almost the same or slightly cooler ( max. 1°C cooler).
So let's assume you are going with 0,5°C cooler leafs aiming for 0,8kPa VPD at night you need 20°C and 62% rH or 22° and 67%rH.

VPD Chart

Vapor pressure deficit (VPD) chart & calculator for horticulture in controlled environment. Cannabis, tomatoes, leafy greens, cucumber.

vpdchart.com

 

[Phytoplankton]

VPD is not an absolute thing, it's a range. Think of plants grown outdoors, the VPD changes drastically on a daily and sometimes hourly basis. Landrace cold climate strains and warm climate strains have different preferences, but most strains are nowhere near pure anymore. Cannabis can handle a huge range of conditions and still thrive. Use the VPD chart as a guide, not a bible.

 

[Rocket Soul]

VPD is not an absolute thing, it's a range. Think of plants grown outdoors, the VPD changes drastically on a daily and sometimes hourly basis. Landrace cold climate strains and warm climate strains have different preferences, but most strains are nowhere near pure anymore. Cannabis can handle a huge range of conditions and still thrive. Use the VPD chart as a guide, not a bible.

I agree, instead of targeting an exact vpd use it as a guide to grt your plant to transpire properly: if the plant looks a bit saggy its not drinking properly, which means make adjustments. VPD tells you in which way to take those adjustments but you still have to be reading your plants. When it is drinking fast and and hav a great praying leaf boner stances then youve arrived

For vpd resources i recommend vpdchartdotcom , it allows you to adjust with sliders and you can set your leaf temp +-

Also remember; vpd is not the only factor that controls the stomata or affect drinking. Other factors included:
Air movement- more movement more drinking
Co2: less transpiration
Blue/green in the spectrum: blue response opens the stomata and green inhibits blue response.
Last but most important: higher light intensity will open the stomata, but you have to have roots and nutes to keep your plant fed.