VPD (Vapor Pressure Deficit)

Vapor Pressure Deficit (VPD) combines temperature and relative humidity into a single number that describes the 'drying power' of the air around your plants — and therefore how readily they transpire and take up nutrients. Dialing VPD into the optimal range for each growth stage (lower in veg, higher in flower) improves growth rate and reduces mold and nutrient problems. Advanced indoor growers use VPD charts instead of managing temperature and humidity separately.