With this tool, you can easily calculate the Vapor Pressure Deficit of your grow room’s air.

First, choose your temperature units: Fahrenheit or Celsius. Then plug in the air temperature and relative humidity and click “Calculate.” The resulting VPD (kPa) will be color-coded to indicate whether the grow room climate is humid (blue), vegetative (green), reproductive (yellow), or dry (purple).

The desired VPD depends on the type of plant, its stage of growth, and, in some cases, the time of day. In general, leafy greens, microgreens, and other non-flowering plants enjoy a “vegetative” environment. Flowering and fruiting plants benefit from a “reproductive” environment. Cannabis plants may yield more trichomes and terpenes, if exposed to a “dry” and water-stressed environment in the days leading up to harvest. And a “humid” nighttime environment can improve translocation of nutrients and metabolites to strawberries and other fruiting plants.