Hey everyone, I wanted to share my tried-and-true philosophy on managing Vapor Pressure Deficit (VPD). After years of dialing this in, I always come back to the idea that you need to treat VPD dynamically to precisely influence nutrient and water uptake throughout the plant's life cycle. The goal isn't just to keep the VPD 'safe,' it's to use it as a powerful throttle to dictate how fast and how hard the plants are working.
Early Vegetative Growth (.8–.9 kPa)
In the early veg phase, I target a low VPD of .8–.9 kPa. This range is key because it minimizes water stress and keeps the leaf stomata wide open. This allows for the fastest possible transpiration and CO2 exchange, which is critical for rapid tissue generation and building mass. Run it hot and humid, keeping temperatures between 78°F and 82°F. Keep the gas pedal down as long as the plants are moving fast and hard.
Late Veg / Stretch / Transition (1.0–1.1 kPa)
As soon as you see vertical movement or stretch, it's time to transition. Bump the VPD up a tiny amount to 1.0–1.1 kPa. This isn't to dry them out, but to tighten internodes and signal the plant to switch gears metabolically. The slight increase helps control stretch and encourages a thick, compact structure without choking transpiration. The higher you raise the VPD, the slower the plants take up water and nutrients, you want to modulate and control their uptake but still keep the pedal to the floor. I’ll hold temperatures around 78°F still, but I quit targeting 80°F at this point.
Early to Mid Flower (1.2–1.3 kPa)
The period of early to mid-flower is where I hold the environment for the longest time, targeting 1.2–1.3 kPa. This is the sweet spot as it strikes the best balance between resin development, optimal gas exchange, and safe relative humidity (RH) for bulking. I keep temperatures between 75°F and 78°F until the final four weeks or so. You want them bulking and putting on mass for as long as possible; you start throttling down their uptake and choking them out when you go higher, and they slow down packing on weight.
Late Flower / Final Phase (1.4–1.5 kPa)
Only when the flowers get very fat and the risk of internal humidity rises do I push the VPD up to 1.4–1.5 kPa. This is almost never before the final 10–14 days. This higher VPD helps pull moisture from the buds, significantly reducing the risk of mold. It’s a judgment call, but with good airflow management, you shouldn't need this high range until the very, very end. In this final phase, I'll drop temperatures to around 70°F to 75°F, sometimes taking them down to 68°F to 70°F in the last two weeks to enhance final characteristics.
Happy growing!
Let me know what you think of this dynamic approach, if you learned something, and what you run!
Early Vegetative Growth (.8–.9 kPa)In the early veg phase, I target a low VPD of .8–.9 kPa. This range is key because it minimizes water stress and keeps the leaf stomata wide open. This allows for the fastest possible transpiration and CO2 exchange, which is critical for rapid tissue generation and building mass. Run it hot and humid, keeping temperatures between 78°F and 82°F. Keep the gas pedal down as long as the plants are moving fast and hard.
Late Veg / Stretch / Transition (1.0–1.1 kPa)As soon as you see vertical movement or stretch, it's time to transition. Bump the VPD up a tiny amount to 1.0–1.1 kPa. This isn't to dry them out, but to tighten internodes and signal the plant to switch gears metabolically. The slight increase helps control stretch and encourages a thick, compact structure without choking transpiration. The higher you raise the VPD, the slower the plants take up water and nutrients, you want to modulate and control their uptake but still keep the pedal to the floor. I’ll hold temperatures around 78°F still, but I quit targeting 80°F at this point.
Early to Mid Flower (1.2–1.3 kPa)The period of early to mid-flower is where I hold the environment for the longest time, targeting 1.2–1.3 kPa. This is the sweet spot as it strikes the best balance between resin development, optimal gas exchange, and safe relative humidity (RH) for bulking. I keep temperatures between 75°F and 78°F until the final four weeks or so. You want them bulking and putting on mass for as long as possible; you start throttling down their uptake and choking them out when you go higher, and they slow down packing on weight.
Late Flower / Final Phase (1.4–1.5 kPa)Only when the flowers get very fat and the risk of internal humidity rises do I push the VPD up to 1.4–1.5 kPa. This is almost never before the final 10–14 days. This higher VPD helps pull moisture from the buds, significantly reducing the risk of mold. It’s a judgment call, but with good airflow management, you shouldn't need this high range until the very, very end. In this final phase, I'll drop temperatures to around 70°F to 75°F, sometimes taking them down to 68°F to 70°F in the last two weeks to enhance final characteristics.
Happy growing!
Let me know what you think of this dynamic approach, if you learned something, and what you run!
