Autoflower VPD Chart 2026: Stage-by-Stage Targets for Faster Harvests
Autoflower VPD chart with exact kPa targets for each growth stage — seedling, early veg, late veg, and bloom. Includes temperature/humidity tables and how autos differ from photoperiods.
Why VPD Matters More for Autoflowers
Vapor Pressure Deficit (VPD) measures the difference between the amount of moisture in the air and the maximum moisture the air can hold at a given temperature. For autoflowers, getting VPD right is especially critical because:
1. Compressed timeline: Autos have 8–12 week total grow cycles. Any week spent at wrong VPD is proportionally more damaging than with photoperiods.
2. No recovery time: Autos can't be kept in veg to recover from stress. Wrong VPD during the 3-week stretch (weeks 4–7) directly cuts final yield.
3. Sensitivity to humidity swings: Autoflowers are predominantly ruderalis genetics — they evolved in arid, continental climates. High humidity during bloom consistently causes more bud rot issues in autos than in photoperiods of equivalent size.
VPD is expressed in kilopascals (kPa). The ideal range for cannabis is 0.8–1.5 kPa depending on growth stage. For a deeper primer on VPD science, see our
Complete VPD Guide.
Autoflower VPD Chart by Stage
| Week |
Stage |
Target VPD (kPa) |
Temp °F (°C) |
RH % |
Notes |
| 1 | Seedling | 0.4–0.8 | 72–77°F (22–25°C) | 65–80% | High RH compensates for undeveloped roots |
| 2 | Early Veg | 0.8–1.0 | 74–80°F (23–27°C) | 60–70% | Begin reducing RH as roots establish |
| 3–4 | Late Veg / Pre-flower | 1.0–1.2 | 75–82°F (24–28°C) | 55–65% | Autos begin showing sex — keep stable |
| 5–6 | Early Bloom / Stretch | 1.0–1.3 | 74–80°F (23–27°C) | 50–60% | Critical phase — maintain RH below 60% |
| 7–8 | Mid Bloom | 1.2–1.5 | 70–77°F (21–25°C) | 45–55% | Reduce temp and RH to prevent bud rot |
| 9–10 | Late Bloom / Ripening | 1.3–1.6 | 65–75°F (18–24°C) | 40–50% | Lower temps boost terpene and resin production |
| 11+ | Final Flush / Harvest | 1.4–1.8 | 65–72°F (18–22°C) | 35–45% | Push VPD high to stress-trigger trichome production |
How Autoflower VPD Differs from Photoperiod VPD
The VPD targets are similar between autos and photos, but the management approach differs:
Speed of transitions: With photos, you can keep plants in veg until VPD is optimized. With autos, the plant dictates timing. You must have your environment dialed before seeds go in — there's no waiting for ideal conditions.
Humidity tolerance in bloom: Many autoflower genetics have tighter bud structure than photoperiod sativas, making them more susceptible to bud rot at high humidity. Keep RH below 55% from week 6 onward — more aggressively than with loosely structured photoperiod strains.
Temperature ceiling: Autoflowers are slightly more heat-sensitive than most photoperiod indicas. Avoid sustained temperatures above 82°F (28°C) during bloom. Heat stress slows trichome development and can force early senescence in compact auto genetics.
Night temperature drop: A 10–15°F (5–8°C) day/night temperature differential during late bloom promotes anthocyanin (purple colour) expression in strains with that genetic potential and increases terpene production in all strains.
Equipment for Hitting Autoflower VPD Targets
Measuring VPD: You need a thermometer/hygrometer that reads both temperature and relative humidity simultaneously. Place it at canopy height — not on the tent wall. Canopy-level readings are the ones that matter.
Raising VPD (lowering RH or raising temp):
— Increase exhaust fan speed to remove humid air
— Add a small dehumidifier for large tents (4x4+)
— Raise light height slightly to increase ambient temperature
Lowering VPD (raising RH or lowering temp):
— Add a small ultrasonic humidifier (for seedling/early veg)
— Reduce exhaust speed to retain more moisture
— Lower ambient temperature via AC or night cycle adjustment
Rule of thumb: It's always easier to lower RH than raise it. Start your grow at the high end of acceptable humidity and progressively reduce — fighting high humidity in late bloom is far harder than maintaining low humidity from the start.
See our
Grow Tent Humidity Control Guide for specific equipment recommendations.
Frequently Asked Questions
What VPD should autoflowers be at?
Seedling: 0.4–0.8 kPa. Early veg: 0.8–1.0 kPa. Pre-flower/late veg: 1.0–1.2 kPa. Early bloom: 1.0–1.3 kPa. Mid bloom: 1.2–1.5 kPa. Late bloom: 1.3–1.6 kPa. Final ripening: 1.4–1.8 kPa. Keep RH below 55% from week 6 onward to prevent bud rot.
Is VPD the same for autoflowers and photoperiods?
Target kPa ranges are similar, but autoflowers require more proactive management because you can't delay flowering to optimize conditions. Autoflowers are also generally more susceptible to bud rot at high humidity and more heat-sensitive in bloom. Have your environment dialed before seeds go in rather than adjusting reactively.
What temperature and humidity for autoflowers in flower?
Early flower: 74–80°F (23–27°C), 50–60% RH. Mid flower: 70–77°F (21–25°C), 45–55% RH. Late flower: 65–75°F (18–24°C), 40–50% RH. Final weeks: 65–72°F (18–22°C), 35–45% RH. Progressive reduction in both temperature and humidity as harvest approaches maximises trichome and terpene production.
How do I calculate VPD for autoflowers?
VPD = SVP × (1 - RH/100), where SVP (saturation vapor pressure) at a given temperature can be calculated as 0.6108 × e^(17.27 × T / (T + 237.3)) with T in Celsius. At 25°C and 60% RH: SVP = 3.17 kPa, VPD = 3.17 × 0.40 = 1.27 kPa. Most growers use a VPD chart or calculator rather than manual calculation.
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