Plant Vapor Pressure Deficit (VPD) Table
Look up VPD values for any combination of temperature and relative humidity.
Quickly find if your growing environment is in the optimal VPD zone for each growth stage.
VPD and Plant Biology Vapor Pressure Deficit (VPD) describes the “drying power” of air — the difference between what moisture the air holds and what it could hold at that temperature. VPD directly drives plant transpiration through stomata (the tiny pores on leaves). When VPD is optimal, stomata stay open to allow CO₂ uptake and water vapor release. Closed stomata (too high or too low VPD) stop both gas exchange and nutrient transport.
Transpiration and Nutrient Uptake As water evaporates from leaf surfaces, the plant draws more water up from the roots — this is the transpiration stream. The transpiration stream also carries dissolved nutrients (calcium, magnesium, boron) upward. Without sufficient VPD-driven transpiration, calcium deficiencies and tip burn can occur even in nutrient-rich soil. This is why VPD matters for quality as much as for yield.
The Saturation Vapor Pressure Formula Saturation Vapor Pressure (SVP) in kPa at temperature T°C: SVP = 0.6108 × e^(17.27 × T / (T + 237.3)) — the Magnus-Tetens formula. At 20°C: SVP = 2.34 kPa. At 25°C: SVP = 3.17 kPa. At 30°C: SVP = 4.24 kPa.
VPD = SVP × (1 − RH/100) At 25°C, 60% RH: VPD = 3.17 × 0.40 = 1.27 kPa — ideal vegetative growth.
Growth Stage Targets Propagation / cuttings: 0.4–0.8 kPa — mist frequently, stomata just learning to function. Seedlings (first 2 weeks): 0.4–0.8 kPa — protect from dehydration. Vegetative (established): 0.8–1.2 kPa — promote vigorous growth. Early flower: 1.0–1.5 kPa — balance between growth and mold prevention. Late flower / finish: 1.2–1.6 kPa — enhanced terpene and resin production.
Temperature and VPD Interaction Raising temperature without adjusting humidity dramatically increases VPD. At 20°C and 70% RH: VPD = 0.70 kPa (vegetative-appropriate). At 30°C and 70% RH: VPD = 1.27 kPa (still good but warmer). At 30°C and 50% RH: VPD = 2.12 kPa (stress territory — too high for most crops).
Practical VPD Management Use a digital thermometer/hygrometer placed near the plant canopy, not the ceiling. HVAC systems can reduce temperature and humidity simultaneously — use a dehumidifier separately to reduce RH while maintaining temperature. Increasing CO₂ concentration (to 1200–1500 ppm) allows plants to keep stomata open at higher VPD without stress. Night cycles typically have lower VPD as temperature drops — manage accordingly.