Vapor Pressure Deficit

Vapor Pressure Deficit (VPD) is a measurement of the difference between the amount of moisture the air can hold at a given temperature versus the amount it actually holds. In cultivation, VPD directly influences transpiration rates—the speed at which plants release water through their leaves. Breeders and cultivators monitor VPD because it affects nutrient uptake, disease susceptibility, and phenotypic expression across different growing environments. Understanding VPD is particularly relevant when stabilizing genetics across varied climate zones, since the same cultivar may express differently under low versus high vapor pressure conditions. VPD ranges are typically categorized as optimal (0.8–1.5 kPa for most growth stages), suboptimal, or excessive, each producing distinct plant responses.

Breeders working in diverse geographic regions use VPD data to identify which parent plants and resulting offspring maintain stable structure, vigor, and terpene profiles across high-humidity and low-humidity environments. Selecting for VPD-resilient genetics helps establish cultivars that perform consistently whether grown in sealed indoor systems or variable outdoor conditions.