VPD explained: How VPD helps you dry perfectly
When it comes to drying, many people first think of temperature and humidity – of course, both are important. But their interaction is crucial. This is exactly what the Vapor Pressure Deficit (VPD) describes. It is therefore a real game changer for the quality and aroma of your flowers.
What is perfect drying?
Perfect drying means preserving the valuable, volatile components of your flower – such as terpenes and cannabinoids – in the best possible way. To achieve this, it is essential to leave the cell structure of the plant intact. Removing water too quickly during drying leads to the collapse of these cell walls, resulting in a loss of aromas and quality in the flower. This is precisely where VPD-controlled drying comes in.
What is behind the VPD principle?
VPD stands for “vapor pressure deficit”. It describes the difference between the moisture in the plant and the air. If this difference is optimal, transpiration functions ideally.
👉 Is the VPD too low? Then the air is too saturated with moisture – the plant can only evaporate a small amount of water. The water remains in the flowers – a risk for mold.
👉 Is the VPD too high? Then the air “sucks” water from the plant too quickly. The result: cell collapse, external shrinkage and structural instability of the flower. The broken cell structure causes the aroma to evaporate and with it the potency of your flower
📊 VPD vs. humidity - why 60% alone is not enough
Many growers focus primarily on the relative humidity – but without reference to temperature, this value is not as constant as you might think. This is because drying at 60% and 16 °C is much gentler than at 60% and 22 °C. Only the VPD shows the real drying speed.
🌓 Attention: VPD changes with temperature changes
- During the day: Grow room usually slightly warmer ➝ VPD increases (at constant humidity)
- At night: grow room cools down ➝ VPD decreases (at constant humidity)
👉 You should therefore keep an eye on the 24-hour climate. Especially at night, there is an increased risk of mold if the VPD is too low.
The optimal VPD
The optimum VPD for drying is between 0.8 and 1.0 kPa – in this range:
- the plant material loses moisture evenly,
- terpenes are largely preserved,
- the risk of mold is significantly reduced.
💡 Rule of thumb: As quickly as necessary, but as gently as possible.
Conclusion: VPD = your new best friend
With VPD, you can precisely control the drying climate – independently of generalized RH values. The result: better quality, more intense aroma and reliable mold prevention.
