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Cannabis Grow Room Temperature and Humidity Chart (2025 Guide)
If you want bigger yields, better terpenes, and smoother smoke, it all starts with the right temperature and humidity. Mastering your grow room climate is one of the simplest ways to turn average buds into top-shelf flower.
This 2025 guide breaks down the ideal grow room temp and humidity chart for every stage of growth, from seedling to harvest, plus expert tips for control and troubleshooting.
Why Temperature and Humidity Matter
Cannabis thrives in a Goldilocks zone, not too hot, not too dry.
- Temperature affects growth rate, transpiration, and nutrient uptake.
- Humidity controls how much water the plant releases through its leaves and directly impacts mold risk.
The wrong balance can cause stunted growth, nutrient burn, or even bud rot, so think of your grow tent’s environment as the invisible nutrient your plants need every day.
The Ideal Grow Room Temperature & Humidity Chart
| Growth Stage | Light Cycle | Temp (Lights On) | Temp (Lights Off) | Relative Humidity (RH) | CO₂ Optional? | Notes |
|---|---|---|---|---|---|---|
| Seedling | 18–24h | 72–78°F (22–26°C) | 70–75°F (21–24°C) | 65–70% | No | Warm & humid helps roots develop; gentle airflow |
| Vegetative | 18/6 | 73–82°F (23–28°C) | 68–75°F (20–24°C) | 55–65% | Yes | Slightly higher temps & humidity speed growth |
| Early Flower (Weeks 1–3) | 12/12 | 70–78°F (21–26°C) | 65–72°F (18–22°C) | 50–55% | Yes | Start lowering humidity to prevent mildew |
| Mid Flower (Weeks 4–6) | 12/12 | 68–77°F (20–25°C) | 63–70°F (17–21°C) | 45–50% | Optional | Trichome & terpene production peaks |
| Late Flower (Weeks 7–9) | 12/12 | 65–75°F (18–24°C) | 60–68°F (15–20°C) | 40–45% | No | Lower humidity avoids bud rot & enhances color |
| Harvest / Pre-Dry | — | 60–70°F (15–21°C) | Same | 45–50% | No | Transition gently into drying room conditions |
Quick Reference: VPD (Vapor Pressure Deficit) Sweet Spot
For advanced growers, VPD measures how efficiently plants “breathe.”
- Veg stage VPD: 0.8–1.1 kPa
- Flower stage VPD: 1.2–1.5 kPa
Staying in this range keeps transpiration and nutrient absorption in perfect sync.
Tools to Control Grow Room Climate
- Thermo-Hygrometer: Tracks temp & humidity in real time.
- Inline Fan + Carbon Filter: For air exchange and odor control.
- Oscillating Fans: Move air gently across canopy.
- Humidifier / Dehumidifier: Adjust RH as needed.
- Heater / AC Unit: Maintain consistent temps day and night.
- Controller or Inkbird Sensor: Automates humidity and temp adjustments.
Common Problems & Fixes
| Issue | Likely Cause | Quick Fix |
|---|---|---|
| Leaves curling up | Too hot / too dry | Lower temp, increase humidity |
| Leaves drooping | Too humid / poor airflow | Add fan, lower RH |
| Slow growth | Temps below 68°F | Add gentle heat |
| Mold or mildew | RH above 60% in flower | Increase airflow, use dehumidifier |
| Burnt leaf edges | Lights too close / dry air | Raise lights, raise humidity slightly |
Seasonal Adjustments for Indoor Growers
| Season | Typical Problem | How to Fix |
|---|---|---|
| Winter | Cold nights, low humidity | Add small heater + humidifier |
| Summer | High temps, excess humidity | Run lights at night; boost airflow |
| Spring/Fall | Fluctuations | Use controllers or thermostats for stability |
Pro Tips for Perfect Climate Control
- Measure canopy temp, not just room temp, lights can add +3–5°F at plant tops.
- Keep a 2–5°F drop between day and night to mimic natural conditions.
- During the last week of flower, slightly cooler temps (65°F) enhance color and terpene retention.
- Avoid fans blowing directly on buds, it causes uneven drying and terpene loss.
Visual Summary: The Perfect Grow Room Climate
| Stage | Temp (°F) | Humidity (%) | Environment Goal |
|---|---|---|---|
| Seedling | 72–78 | 65–70 | Root development |
| Veg | 73–82 | 55–65 | Fast, leafy growth |
| Flower (Early) | 70–78 | 50–55 | Stretch & bud set |
| Flower (Late) | 65–75 | 40–45 | Resin & terpene boost |
| Harvest Prep | 60–70 | 45–50 | Smooth transition to drying |
Final Thoughts
Perfect temperature and humidity control turn ordinary grows into high-grade harvests.
Keep your grow room between 70–78°F and 45–60% RH, adjust gradually by stage, and always measure from canopy level.
Once you’ve nailed your grow room climate, check out our Weed Dry Tent Chart to master the post-harvest phase too.
👉 Browse our Blog for strain-specific climate recommendations.
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