Vapor Pressure Deficit is the single most important climate variable in your grow room. Use our interactive calculator to find your ideal range — then learn how Growlink monitors it automatically, 24/7.
Vapor Pressure Deficit (VPD) is the difference between how much moisture the air can hold when fully saturated and how much it actually holds. It’s the driving force behind transpiration — the process that pulls water and nutrients from roots to leaves.
When VPD is right, stomata open, gas exchange flows, and your plants drink efficiently. When it’s off, you get slow growth, nutrient lockout, or mold.
Air temperature and relative humidity are the two primary drivers. As temperature rises, the air’s moisture capacity increases, raising VPD. As humidity rises, VPD drops.
Leaf temperature matters too. Leaves are typically cooler than the surrounding air, which shifts the pressure differential. Accounting for this offset gives you a more accurate “leaf VPD” — the number that actually describes what your plant experiences.
The air is already close to saturation, so plants transpire very slowly. That can reduce cooling, slow nutrient movement through the plant, and increase disease pressure in persistently humid conditions.
The ideal VPD depends on growth stage. Propagation and clones prefer 0.4–0.8 kPa. Vegetative growth thrives at 0.8–1.2 kPa. Flowering typically calls for 1.2–1.6 kPa to drive resin production and density.
The air pulls moisture from leaves aggressively. If roots can’t keep up, stomata close to conserve water — shutting down CO₂ uptake, nutrient transport, and photosynthesis. You’ll see wilting, tip burn, and stress.
Adjust the sliders to match your grow-room conditions. Results update instantly.
Growers who optimize VPD consistently report bigger, denser harvests with fewer crop-loss events. Here’s what the data shows.
Optimized VPD correlates with 15–30% yield increases and denser flower structure.
Keeping VPD above 0.8 kPa during vegetative growth eliminates most conditions for powdery mildew and botrytis.
Optimal VPD in veg means faster internode development and a more uniform canopy — reducing the need for manual training.
Dialing in late-flower VPD between 1.2–1.6 kPa supports maximum terpene and resin expression without sacrificing density.
Dial in shot volume, frequency, and runoff targets based on substrate, pot size, and growth stage.
Open calculatorCalculate the flow rate and tank duration you need to hit your target ppm for any room size.
Open calculatorLearn generative vs. vegetative steering strategies with practical substrate targets and timing.
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