Vapor Pressure Deficit (VPD)

Optimize plant growth by calculating the difference between air moisture saturation and actual humidity.

Environment Conditions

Air Temperature (°C)

Relative Humidity (%)60%

Leaf Temp Offset (°C)

Transpiration Drive

0.91kPa

Vegetative

Leaf Sat VP2.81kPa

Air Actual VP1.90kPa

VPD vs Humidity (at 25°C)

Overview

Vapor Pressure Deficit (VPD) is the difference between how much moisture the air *can* hold and how much it *does* hold. It is the primary driver of plant transpiration.

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Pro Tips

Low VPD (< 0.4 kPa): Risk of fungal growth and over-hydration.
Cloning/Early Veg (0.4 - 0.8 kPa): Ideal for root development and young plants.
Vegetative (0.8 - 1.2 kPa): Optimal for healthy foliage growth.
Late Flower (1.2 - 1.6 kPa): Higher stress, helps prevent bud rot in dense flowers.

Fun Facts

"Think of VPD as the 'thirst' of the atmosphere."
"VPD is independent of temperature, unlike Relative Humidity, making it a better metric."
"Too low VPD (high humidity) stops transpiration -> Calcium deficiency -> Bud rot."
"Measuring Leaf Surface Temperature (LST) is critical for accurate calculation."

Formula: VPD = SatVP(leaf) - ActualVP(air)

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