If you want to pull maximum terpene expression and vigor out of a boutique line, VPD is where the real control lives.
What Is VPD, and Why Does It Matter?
Vapor pressure deficit describes the relationship between temperature and relative humidity, and it directly controls how open a plant's stomata are. That, in turn, governs nutrient uptake and transpiration rate. Get VPD wrong and even perfect genetics will underperform.
Target VPD Windows by Stage
Unrooted cuttings / early rooting: High humidity, 75-85% RH, at 22-25°C, targeting a VPD of 0.4-0.8 kPa.
Vegetative stage: Balanced growth conditions, 55-65% RH, at 24-28°C, targeting a VPD of 0.8-1.1 kPa.
Late bloom / hash production: Low humidity, 40-50% RH, with cooler night temperatures to preserve volatile monoterpenes, targeting a VPD of 1.2-1.5 kPa.
Dial in these windows stage by stage, and you'll see the difference in resin production, aroma, and overall plant resilience, especially on genetics that were bred to reward the effort.