Dial in your temperature and humidity for maximum growth VPD (Vapor Pressure Deficit) is the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at that temperature. It's the single most important environmental metric for cannabis growing — more useful than temperature or humidity alone.
Why VPD Matters
VPD too low (< 0.4 kPa) — stomata close, growth slows, mold risk increases VPD too high (> 1.5 kPa) — plant loses water faster than roots can absorb, wilting and nutrient lockout VPD optimal — stomata stay open, transpiration drives nutrient uptake, plants grow fastest
Practical Tips
Don't chase exact VPD numbers — think in ranges. As your plants move from veg to flower, gradually lower humidity and temperature. Monitor leaf surface temperature if possible — it's typically 3-5°F cooler than air temp. For more growing guides: Nutrients | Watering | Training
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