Climate·9 min read
Mastering VPD: Temperature & Humidity by Stage
Vapour Pressure Deficit (VPD) is the gap between how much moisture the air is holding and how much it could hold. Plants transpire — and therefore feed — based on VPD.
Ideal VPD by Stage
Seedling/clone: 0.4–0.8 kPa. Veg: 0.8–1.2 kPa. Bloom: 1.2–1.5 kPa. Below 0.4 invites mould; above 1.6 stresses plants.
Controlling It
Raise VPD → higher temperature or lower humidity. Lower VPD → the opposite. Humidifiers, dehumidifiers and heaters are your levers.
Measure at Canopy Level
Sensor position matters. Air near the light is drier and hotter than air at the leaf surface — always measure where the plants actually live.
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