VPD (Vapour Pressure Deficit) is the difference between the amount of moisture in the air and the maximum moisture the air can hold at a given temperature. In controlled growing environments, VPD determines the rate of plant transpiration β influencing nutrient uptake, stomatal behaviour, and overall growth rate.
Key Facts
- Measured in kilopascals (kPa); optimal range for most crops is 0.8β1.2 kPa
- Low VPD (high humidity): stomata close, transpiration slows, nutrient uptake drops
- High VPD (low humidity): excessive transpiration, wilting, tip burn risk
- VPD is determined by both temperature and relative humidity together
- Seedlings and clones prefer low VPD (0.4β0.8 kPa); mature plants prefer 1.0β1.5 kPa
- Controlling VPD requires coordinating temperature, humidity, and airflow together