Vapor Pressure Deficit

Vapor Pressure Deficit (VPD) is an environmental metric—not a strain trait—that describes the difference between the amount of moisture air can hold versus what it actually contains. In cannabis cultivation, VPD is used by breeders and growers to optimize conditions during phenotyping and selection, as different cultivars exhibit varying tolerance thresholds to high or low VPD ranges. Lineage records rarely reference VPD directly as a heritable trait, but breeders working in controlled environments document how parent plants respond to specific VPD windows during flowering and vegetative growth. Understanding a strain's VPD response profile can inform breeding decisions about plant vigor, transpiration efficiency, and environmental resilience. This metric is particularly relevant when stabilizing genetic lines across multiple growing environments.

Breeders use VPD monitoring during pheno hunts to identify plants with desirable water-management physiology and stress tolerance. Strains selected under consistent VPD conditions may show altered expression of drought or humidity-stress genes in offspring grown under different environmental parameters.