Cannabis VPD Chart by Growth Stage
Vapor Pressure Deficit (VPD) is the single best metric for tuning your environment. Hit the right window and your plants transpire freely, eat more, and grow faster.
Reviewed
| Stage | Target VPD | Air temp | RH |
|---|---|---|---|
| Clone / Seedling | 0.4 – 0.8 kPa | 77°F | 75–87% |
| Early Veg | 0.8 – 1.1 kPa | 78°F | 66–76% |
| Late Veg | 1.0 – 1.3 kPa | 78°F | 60–69% |
| Early Flower | 1.0 – 1.4 kPa | 77°F | 56–68% |
| Mid Flower | 1.2 – 1.5 kPa | 76°F | 51–61% |
| Late Flower / Ripen | 1.4 – 1.6 kPa | 72°F | 40–48% |
How to read this: the RH column is the humidity that produces the target VPD at the listed air temperature. If you run a different temperature, your target RH shifts, so treat these as a starting point rather than fixed numbers.
Leaf temperature matters. VPD is really driven by leaf temperature, not air temperature. Under strong light a canopy can run a few degrees off ambient. This chart assumes leaf temperature equals air temperature; if you measure leaf temperature with an IR thermometer, adjust your humidity to keep the same VPD.
Humidity is calculated from target VPD and air temperature using the Tetens saturation-vapor-pressure equation, with leaf temperature assumed equal to air temperature (air VPD). Values are rounded to whole-percent RH.
Roots are still developing. Keep humidity high so leaves don't pull water faster than roots can replace it.
Plants are establishing structure. Slightly drier air encourages stronger root growth.
Dial humidity down gradually. Plants should be transpiring strongly.
Stretch phase. Plants want similar VPD to late veg, just slightly cooler.
Buds are bulking. Lower RH helps prevent mold; VPD stays moderate.
Push terpenes and color. Cooler nights, lower RH, but watch for stress at the high end.
Want a printable VPD chart?
PDF cheat sheet you can hang in the grow room.