Ultimate VPD Guide and Calculator / Chart Maker

Hey AFN,

TL;DR: The right VPD makes your plants grow better. VPD = the correct temp & humidity. Link to VPD guide. We'll send you a vpd chart generator / calculator if you drop us your email. If you don't want to, just send me a PM and I'll give you the download link there.

A quick summary of the high points:

Why is VPD important?

VPD helps you identify the correct range of temperature and humidity to aim for in your grow space. With VPD you can achieve the best results while avoiding pest and environmental problems. VPD also controls plant transpiration rates, stomata opening, CO2 uptake, nutrient uptake, and plant stress.

How to calculate air VPD:

A. Figure out the SVP

• SVP = 610.78 x e^(T / (T +238.3) x 17.2694))
  • T is in degrees Celsius
    
    
  • The result, SVP, is in pascals (divide by 1000 to get kPa)

B. Calculate the VPD

• VPD = SVP x (1 – RH/100)
  
  We made a neat VPD calculator (link):
  
  

Ideal VPD For Growing

Ideal VPD, as a general rule for plant growth, is around 0.8 – 1.2 kPa (kilopascals). However, your plants have different needs during different stages of growth. You need to tailor your grow environment to the stage of growth that your plants are in. Here's a link to the ideal VPD ranges for different stages of growth.


Would love to hear your feedback / comments.

--Pete

 

[Tony21]

Very cool man, nice easy overview, good info.

How does the light sensor work, what is it measuring what is the point of this sensor, I mean, why is it there. Does it measure PAR or just lumens?
Should the sensor box be placed in the canopy?

Is it for sale in Europe directly or only ships from the US?

 

[Tony21]

One more question, can the humidity sensor be calibrated and how, other than putting it in a wet salt bag?

 

[okPeet]

Very cool man, nice easy overview, good info.

How does the light sensor work, what is it measuring what is the point of this sensor, I mean, why is it there. Does it measure PAR or just lumens?
Should the sensor box be placed in the canopy?

Is it for sale in Europe directly or only ships from the US?

Hey,

As far as the Pulse ONE goes, the light sensor is just measuring relative light levels. You'd be able to use it to tell if your lights are coming on at the wrong time, nothing as specific as PAR. If you've got good air circulation in your room (and if it's not a very large room), you can place it pretty much anywhere, just around the canopy level.

It ships for $20 to Europe. We've got a few users all over Europe and other parts of the world.

One more question, can the humidity sensor be calibrated and how, other than putting it in a wet salt bag?

It comes pre-calibrated, and you can do your own calibration.

Any more feedback regarding the VPD guide? Looking for specific comments, what parts you liked and didnt, etc.

 

[Nickaflol]

Hello friend. I cant get the chart from pulse through email. They dont sent it to me. I used 2 emails but nothing comes. Do you have a link where you can upload the chart so we can download it?

 

[Simplicio]

If this is what you meant, here's the VPD chart from https://forum.grasscity.com/threads/humidity.1478655/#post-23830049
Subtract 5-7 F from air temp to get leaf temp, then try to stay in the green.

 

[Tommy Bahama]

Here's a little something I put together to make things simple to read...

 

[okPeet]

@Nickaflol Hey sorry to hear you're having issues.

Here are the links:
Excel version VPD chart maker & calculator
Google Doc version VPD chart marker & calculator

 

[lunarman]

Here's a little something I put together to make things simple to read...

View attachment 1010638

thats a great chart. I like to see the different grow phases changing temp and RH thru the cycle.

 

[okPeet]

thats a great chart. I like to see the different grow phases changing temp and RH thru the cycle.

Check out the charts that I linked - you can set the grow phases, leaf temperature offset, and C vs F. You can make pretty much any chart you want!