VPD Value Simply & Detailed Explained – The Invisible Key to Healthy Cuttings
VPD stands for Vapor Pressure Deficit and is one of the most important, yet often underestimated, values when growing cannabis cuttings. It describes how much the air "dries" and how much water the plant can transpire as a result. Optimal VPD ensures perfect transpiration – without stress, without waterlogging, and without the risk of mold.
At Cannaphilie, we recommend keeping an eye on VPD, especially in the first 14 days and during the vegetative phase. Because strong genetics only unfold their full potential when the environmental conditions are right.
What exactly is VPD?
The air can only absorb a certain amount of water vapor (saturation vapor pressure). The VPD is the difference between this maximum possible vapor pressure and the current vapor pressure in your grow room. The higher the VPD, the "hungrier" the air is for moisture – the plant transpires more strongly.
Why is VPD so important for cuttings?
- Too low VPD → too high humidity → risk of mold, slow root formation, and weak growth.
- Too high VPD → too much evaporation → wilting, stress, and closed stomata (the plant can no longer absorb nutrients properly).
- Optimal VPD → ideal transpiration → strong roots, healthy leaves, and maximum nutrient uptake.
Optimal VPD Values for Cannabis Cuttings (2026 Recommendations)
| Phase | VPD (kPa) | Humidity at 22–25 °C | Notes |
|---|---|---|---|
| Cutting / Rooting (Day 1–14) | 0.4 – 0.8 | 70–85 % | High humidity, gentle start |
| Vegetative Phase | 0.8 – 1.2 | 50–70 % | Strong leaf growth |
| Early Flowering | 1.0 – 1.4 | 45–60 % | Good resin production |
| Late Flowering / Maturation | 1.2 – 1.6 | 40–50 % | Intense aroma, lower risk of mold |
How to calculate VPD easily
You only need two measurements:
- Air temperature
- Relative humidity (in %)
Modern apps and VPD calculators (e.g., on your smartphone) perform the calculation automatically. The rule of thumb is:
VPD = Saturation Pressure(Temperature) – Current Vapor Pressure
There are ready-made VPD tables and free calculators – you don't have to be a math genius.
Practical tips from Cannaphilie
- In the first 10 days, it's better to keep the VPD slightly lower and then gradually increase it.
- Combine VPD with a slight airflow (small fan) – this prevents stagnant air and promotes strong stems.
- Strong genetics from Cannaphilie tolerate small fluctuations better because they are bred to be robust and vital.
A good VPD value is like an invisible "co-coach" for your cuttings – it ensures they grow in harmony with the environment from the very beginning.
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