VPD Chart for Weed: Best VPD by Growth Stage
Quick answer: VPD (vapor pressure deficit) measures how ‘thirsty’ the air is, and the best VPD for cannabis rises as the plant grows: roughly 0.4-0.8 kPa for seedlings, 0.8-1.1 kPa in veg, and 1.2-1.5 kPa in flowering. Hitting the right VPD for each stage drives healthy transpiration, faster growth and better buds. Use the chart below to set your temperature and humidity.
VPD, or vapor pressure deficit, is one of the most useful environmental numbers in indoor growing, yet it is often ignored in favour of plain temperature and humidity. It describes the difference between how much moisture the air is holding and how much it could hold, which in turn controls how fast your plants transpire.
Recommended Strains
Cream Candy Auto
|
THC | 19% - 24% (High) |
|
Type | Autoflowering |
|
Yield | High |
|
Phenotype | 80% Indica / 20% Sativa |
Cream Caramel
|
|
THC | 19% - 24% (High) |
|
|
Type | Feminized |
|
|
Yield | High |
|
|
Phenotype | 90% Indica / 10% Sativa |
Get VPD right and your plants open their stomata, transpire efficiently, take up more nutrients and grow vigorously. Get it wrong and you see deficiency-like symptoms, slow growth or mold, even with perfect nutrients. The chart below gives the target VPD for each stage; the sections after explain what it means and how to hit it.
| Stage | Target VPD (kPa) | Why |
|---|---|---|
| Seedlings / clones | 0.4 – 0.8 kPa | Low transpiration; keep humidity high |
| Early / mid vegetative | 0.8 – 1.1 kPa | Steady growth; moderate transpiration |
| Late veg / early flower | 1.0 – 1.3 kPa | Stronger transpiration and nutrient uptake |
| Mid / late flower | 1.2 – 1.5 kPa | Drier air helps bud quality and limits mold |
What Is VPD?
In plain terms, warm air can hold more water vapour than cool air. VPD is the gap between the moisture the air currently holds and the maximum it could hold at that temperature. A low VPD means humid, ‘full’ air where plants transpire slowly; a high VPD means dry, ‘thirsty’ air that pulls moisture out of the plant quickly.
Because VPD combines temperature and humidity into a single figure, it is a better guide to how your plants actually feel than either number alone. That is why two grow rooms with the same humidity can behave very differently, and why dialling in VPD solves problems that adjusting humidity by itself does not.
Promos & Deals
Why VPD Matters for Your Plants
Plants ‘breathe’ through tiny pores called stomata, taking in CO2 and releasing oxygen and water vapour. VPD controls how open those stomata are: at the right VPD they stay open, transpiration flows, and with it comes nutrient uptake and strong photosynthesis for vigorous growth.
Stray too far either way and growth suffers. Too low a VPD (humid air) slows transpiration, invites mold and can mimic nutrient problems; too high a VPD (dry air) forces the plant to close its stomata to avoid losing water, stalling growth and stressing it. The sweet spot shifts as the plant matures, which is exactly why the chart is staged.
How to Hit the Right VPD
Since VPD comes from temperature and leaf-to-air humidity together, you hit your target by adjusting both. Raise VPD (drier) by warming the room or lowering humidity; lower VPD (more humid) by cooling slightly or adding humidity. Measure with a thermo-hygrometer, and ideally account for leaf temperature, which usually runs a few degrees below air temperature.
In practice, humidity control is where most growers win or lose. To bring humidity down in flower, see our guides to lowering grow-tent humidity and the importance of a dehumidifier. If you grow autoflowers, our autoflower VPD chart covers their specifics.
Leaf Temperature and Measuring VPD
For accurate VPD you ideally use leaf temperature, not just air temperature, because the surface of a transpiring leaf usually sits a few degrees cooler than the surrounding air. Ignoring this makes your real VPD higher than your calculator suggests, which can quietly stress plants that look fine on paper.
In practice, measure air temperature and relative humidity with a reliable thermo-hygrometer at canopy height, and if you can, check leaf temperature with an infrared thermometer and subtract a couple of degrees as a rough adjustment. A VPD calculator or chart then turns those readings into a single number you can steer by, which is far more useful than watching humidity alone.
FAQs
What is the best VPD for cannabis?
It changes by stage: roughly 0.4-0.8 kPa for seedlings and clones, 0.8-1.1 kPa in vegetative growth, and 1.2-1.5 kPa in flowering. Higher VPD (drier air) suits later stages, while young plants need lower VPD (more humidity). Adjust temperature and humidity together to hit the target for each stage.
What is the best VPD for flowering?
Around 1.2-1.5 kPa during mid to late flowering. The drier air at this higher VPD supports strong transpiration and nutrient uptake while helping to keep humidity low enough to protect dense buds from mold. Ease into it from about 1.0-1.3 kPa in early flower rather than jumping straight to the top of the range.
What happens if VPD is too high or too low?
Too high (air too dry) makes plants close their stomata to save water, stalling growth and causing stress and nutrient issues. Too low (air too humid) slows transpiration, reduces nutrient uptake and raises the risk of mold and mildew. Keeping VPD in the stage-appropriate range avoids both problems.
What is a good VPD for seedlings?
Low, around 0.4-0.8 kPa. Young seedlings and clones have small root systems and transpire little, so they need humid air (a low VPD) to avoid drying out. As they establish and grow, gradually raise VPD into the vegetative range of about 0.8-1.1 kPa. Too high a VPD this early stresses tender plants.
Is VPD more important than humidity?
VPD is more useful, because it combines temperature and humidity into one figure that reflects how the plant actually experiences the air. Two rooms with identical humidity can have very different VPD at different temperatures. Steering by VPD, rather than humidity alone, solves environmental problems that adjusting humidity by itself often does not.
How do I lower VPD if it is too high?
Raise humidity or lower the temperature slightly, since VPD depends on both. Adding a humidifier, misting (for seedlings), lowering light intensity or cooling the room all bring VPD down. Make changes gradually and re-measure, aiming for the target range for your plants current growth stage.
