Cannabis VPD Chart — ideal VPD, temperature & humidity by growth stage
VPD (Vapor Pressure Deficit) is the single most useful number in a grow tent: it tells you how hard the air is pulling water from your plant's leaves, which drives transpiration, nutrient uptake, and growth rate. This is the complete VPD chart by stage — plus a free calculator to check your exact conditions.
Green = dialed in · blue = too low (raise VPD) · red = too high (lower VPD). Leaves run ~2°C cooler than air under LED; set the offset to 0 for plain air VPD.
VPD chart by growth stage
These are the environment bands Cultivar grades real grow journals against. Ranges are guidelines for typical indoor cannabis; individual cultivars vary.
| Stage | VPD (ideal) | Temperature | Relative humidity |
|---|---|---|---|
| Germination | 0.4–0.8 kPa | 22–26°C (72–79°F) | 70–80% |
| Cutting | 0.2–0.6 kPa | 22–26°C (72–79°F) | 80–95% |
| Seedling | 0.5–0.8 kPa | 20–25°C (68–77°F) | 65–75% |
| Vegetative | 0.8–1.1 kPa | 22–28°C (72–82°F) | 55–70% |
| Flowering | 1–1.4 kPa | 20–26°C (68–79°F) | 40–55% |
| Late flower / flush | 1.2–1.5 kPa | 18–24°C (64–75°F) | 40–50% |
How to read the VPD chart
Early life wants LOW VPD (high humidity, gentle transpiration) because young roots can't keep up with water demand. As the plant builds root mass you raise VPD to drive water and nutrient flow. Late flower runs the driest — partly for density and resin, mostly to keep botrytis out of dense buds. The plant is the real gauge: leaf curl or slow growth at a "correct" VPD means your cultivar wants something different.
VPD for veg
During vegetative growth, target 0.8–1.1 kPa. Sit at the lower end (~0.8) in early veg while the root system is still filling in, and drift toward 1.1 as the plant matures and transpires harder. At about 25°C air temperature that works out to roughly 60–65% RH with a 2°C leaf-temperature offset. Too low and growth crawls; too high and you get soft, stretchy growth and a pest-friendly canopy.
VPD for flowering
In flower, target 1.0–1.4 kPa, then let it drift to 1.2–1.5 kPa in late flower and flush. At around 24°C that's roughly 45–55% RH, stepping the humidity down as buds fatten. Keeping late-flower air on the drier side is your main defense against botrytis (bud rot) in dense colas. Plug your exact numbers into the calculator above and match them to the flowering band.
How to dial in VPD, step by step
- Pick your stage. Choose germination, seedling, veg, flower, or flush — each wants a different VPD band (see the table).
- Measure temp and humidity at canopy height. Use a sensor beside the plants, not on the tent wall. Log it — the number you don't record is the number you can't fix.
- Estimate leaf temperature. Subtract ~2°C from air temp under LED (leaves run cooler). Set the offset in the calculator, or use an IR thermometer on a fan leaf for the real value.
- Compute VPD and compare to your stage band. Use the calculator above. Green = dialed in; blue = too low (raise VPD); red = too high (lower VPD).
- Adjust one lever and re-check. Nudge temperature, humidity, or airflow, then re-measure. Small changes move VPD a lot near the edges.
How to raise or lower VPD
Lower VPD (air is too dry / hot for the stage): add a humidifier, drop temperature, ease off airflow, or add a humidity dome for seedlings and clones. Raise VPD (air is too humid / cool): run a dehumidifier, raise temperature, increase exhaust and airflow, or defoliate to cut canopy humidity. Change one lever, re-measure, repeat — near the band edges a 1–2°C or 5% RH shift moves VPD a surprising amount.
Why VPD beats reading temperature and humidity alone
VPD is non-linear in temperature and humidity, so two readings that each look fine can combine to a VPD outside the ideal band. That's why a tent at 28°C and 65% RH can read "green" on both gauges yet stress the plant. Judge by the VPD number and let it tell you which lever to move.
Stop calculating it by hand
Everything above is a snapshot. VPD moves all day — it climbs as the lamp heats the canopy, and it swings hard in the hour after lights-off when temperature drops and relative humidity spikes. A chart tells you the target; it cannot tell you whether you hit it at 3am.
Any cheap smart hygrometer can. Connect a Govee, SwitchBot, Inkbird, AC Infinity or Ecowitt sensor — or anything Home Assistant can read — and Cultivar logs temperature, humidity and the derived VPD on its own, grades every reading against the stage band on this page, and shows you the drift you would otherwise never see.
- VPD computed for you, per reading, from your own sensor — no arithmetic, no spreadsheet.
- Graded against the stage band above, so "in range" is measured rather than eyeballed.
- Drift alerts when the combination moves out of band, including overnight.
- Plugs that react — a rule like "RH over 65% in flower → exhaust fan ON" runs whether or not you are awake.
Free to use, no card. If you would rather see the sensors first, the automatic VPD monitoring guide covers which ones work, what they cost, and the trade-offs between cloud and local.
Related tools & guides
Prefer to type numbers? Use the standalone VPD calculator. See also the deficiency chart, pH chart, and dry & cure guide, or browse the 20,726-strain library for per-strain flowering times and targets.
VPD FAQ
What is VPD?
Vapor Pressure Deficit (kPa) combines temperature and humidity into one number describing how hard the air pulls moisture from a leaf. It predicts transpiration — and therefore water and nutrient uptake — far better than temperature or humidity alone.
What is a good VPD for cannabis?
It depends on stage. Seedlings and clones want a low VPD (0.4–0.8 kPa, high humidity); vegetative plants 0.8–1.1 kPa; flowering 1.0–1.4 kPa; late flower / flush 1.2–1.5 kPa. Use the calculator above to check your exact temp and humidity against your stage.
What VPD is ideal during flowering?
Roughly 1.0–1.4 kPa for most cannabis cultivars in mid flower, drifting toward 1.2–1.5 kPa late in flower as you lower humidity to protect dense buds from botrytis (bud rot).
What VPD is best for veg?
0.8–1.1 kPa is the vegetative sweet spot — enough transpiration to drive fast, healthy growth without stressing the plant. Early veg can sit at the lower end; late veg toward the top as the root system fills in.
How do I calculate VPD?
Air VPD = (1 − RH/100) × SVP(air), where SVP = 0.6108 × e^(17.27·T/(T+237.3)) with T in °C. Leaf VPD (more accurate) uses the leaf temperature, which runs a couple of degrees below air temp under LED: VPD = SVP(leaf) − (RH/100 × SVP(air)). The calculator above does both.
What is leaf temperature offset?
Leaves are usually 1–3°C cooler than the surrounding air under LED (and can be warmer under HPS). Because VPD is driven by the leaf surface, subtracting a leaf offset (default 2°C) gives a truer number than air temperature alone. Set it to 0 for plain air VPD.
How do I lower VPD?
Lower VPD = more humid or cooler air. Add a humidifier, lower the temperature, reduce airflow slightly, or add transpiring plants. Seedlings and clones that want a low VPD often need a humidity dome.
How do I raise VPD?
Raise VPD = drier or warmer air. Run a dehumidifier, increase temperature, add exhaust/airflow, or defoliate to reduce canopy humidity. Late flower usually needs the driest air to stay ahead of mold.
Why is my VPD out of range when temp and humidity look fine?
VPD is non-linear: two readings that each look acceptable can combine to a VPD outside the band (e.g. 28°C at 65% RH). Always judge by the VPD number, not temp and humidity in isolation — that is exactly what this chart and calculator are for.
Does VPD matter more than temperature or humidity?
For transpiration, yes — VPD captures how temp and humidity act together on the leaf. But you still keep temperature and humidity in their own healthy ranges (roots, enzymes, and mold risk care about the absolute values too). VPD is the tie-breaker that tells you which one to adjust.
Sources: Grossiord et al. 2020, New Phytologist — stomata close as VPD climbs · Adams & Ho 1993, Plant and Soil — calcium uptake tracks transpiration · Inoue et al. 2021, Frontiers in Plant Science — steady VPD beats swinging VPD · Nelson & Bugbee 2015, PLOS ONE — leaf temperature vs air temperature
- Govee H5075 hygrometer — cheap, accurate, logs to your phone — the sensor most Cultivar grows start with
- Inline fan with speed controller — the fastest lever on VPD once temps drift
Affiliate links: we may earn a small commission at no cost to you. We only list gear that solves the problem on this page. Disclosures.
Keep reading
- Run your own numbers in the VPD calculator
- When VPD is right but leaves still look wrong
- Environment targets for drying and curing
Track your own grow free — the journal grades your environment against these bands →
Get the one-page grow reference card
VPD, pH by medium, deficiency symptoms and dry/cure targets on a single printable page. Free — plus the occasional grow-data breakdown. No spam, unsubscribe in one click.