About VPD

What is VPD or Vapor Pressure Deficit?

VPD is the deficit or difference in moisture present in the air vs how much moisture the air could hold. Why is this important? Improper VPD can limit plant growth. So what VPD is good? Below is a table which makes finding the correct VPD easy. Simply go along the left side of the table to locate the temperature. This works best when using the temperature from the plant canopy. However the temperature in the room or grow area can work if the leaf temp is not available. The easiest way to get the temperature off the leaf is just to use a laser thermometer. Once the temperature has been located slide to the right and find the color of the stage of growth the plant is in. This Table is specifically for Cannabis. Once the VPD goal has been located slide up on the table to locate the humidity needed to achieve this. This is important because the correct humidity not only varies based on a plants stage of growth but also the ambient temperature. This takes the guess work out of Temperature and humidity. VPD can increase when lessening the distance between grow light and plant due to leaf temperature rising removing lights or moving them further away can decrease VPD by impacting temperature in this same way. Try to keep the VPD correct while maintaining a proper light distance.

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