VPD for optimum transpiration: measure vapour pressure deficit in kPa from temperature and humidity — seedling 0.4–0.8, veg 0.8–1.2, flower 1.0–1.5 kPa.
VPD measures the water vapour absorption capacity of the air in kPa. Calculated from temperature and humidity. Optimum VPD: Vegetative 0.4-0.8 kPa, flowering 0.8-1.2 kPa. Too low: Fungal risk, low transpiration. Too high: stress, nutrient problems. Use VPD-Calculator for precise environmental control.
VPD stands for vapor pressure deficit and measures the difference between the current humidity and the maximum humidity that the air can hold at a given temperature. An optimal VPD promotes transpiration and the growth of cannabis plants.
VPD can be determined using a hygrometer to measure relative humidity and a thermometer to measure temperature. Based on these values, VPD can be calculated using a VPD table or an online calculator.
During the vegetative phase, VPD values between 0.8 and 1.2 kPa are ideal, while during the flowering phase, values between 1.0 and 1.5 kPa should be targeted to optimize growth and flower development.
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