VPD and Environment

Vapor pressure deficit, or VPD, describes how strongly the air pulls water from leaves. It is the single number that ties temperature and humidity together, and getting it into a comfortable range makes plants drink, feed, and grow steadily.

What VPD means in plain language

Warm air holds more water than cool air. VPD measures the gap between how much water the air holds and how much it could hold at that temperature. A low gap means humid, sluggish air where plants drink slowly and mold risk rises. A high gap means dry air that pulls water fast and stresses leaves.

Comfortable ranges by stage

Seedlings and clones like gentle, humid conditions. Vegetative plants like moderate conditions with steady airflow. Flowering plants like drier air, since dense buds and humidity are a mold risk. Exact numbers depend on your setup, so treat published ranges as targets to approach, not lines to hit perfectly.

Controlling the environment

Control temperature with ventilation and light height, humidity with ventilation and dehumidification, and airflow with fans that keep air moving without blasting plants directly. Measure with a reliable thermometer and hygrometer at canopy height, not at the wall.