Best Temp & Humidity for Growing Cannabis

Growing great cannabis requires the right temperature and humidity. Here’s a quick overview:

Growth Stage	Temperature (°F)	Humidity (%)
Seedling	75-80	70-80
Vegetative	68-78	45-55
Flowering	65-75	35-45
Drying/Curing	60-70	45-55

Key points:

Conditions change as plants grow
Vapor Pressure Deficit (VPD) matters for plant health
Use thermometers, hygrometers, fans, and dehumidifiers
Check and adjust regularly

Controlling your grow environment is crucial. Pay attention to your plants and you’ll be on track for a great harvest.

Basics of Temperature and Humidity for Cannabis

Temperature and humidity can make or break your cannabis grow. They work together to create the perfect environment for your plants.

Temperature affects how fast cannabis grows. The sweet spot is usually 70-80°F (21-29°C). Here’s why:

Too hot: Plants might wilt or grow slowly
Too cold: Growth slows and mold becomes a risk

Humidity is the amount of water in the air. It’s measured as relative humidity (RH) and it’s super important:

High humidity: Helps young plants drink through their leaves
Low humidity: Makes mature plants produce more resin

Temperature and humidity have a complex relationship. That’s where Vapor Pressure Deficit (VPD) comes in. VPD measures the difference between the moisture in the air and how much it can hold. It affects how well plants can "breathe" and grow.

VPD Range (kPa)	Growth Stage	Effect on Plants
0.5 – 0.7	Clones	Helps roots grow
0.7 – 1.0	Vegetative	Boosts leaf growth
1.0 – 1.4	Flowering	Increases resin production

The right VPD helps plants move water and nutrients efficiently.

These factors change based on the plant’s stage:

1. Seedling Stage

Temperature: 75-80°F (24-27°C)
Humidity: 70-80% RH

2. Vegetative Stage

Temperature: 68-78°F (20-26°C)
Humidity: 45-55% RH

3. Flowering Stage

Temperature: 65-75°F (18-24°C)
Humidity: 35-45% RH

4. Late Flowering

Temperature: 60-70°F (16-21°C)
Humidity: 45-55% RH

To keep these conditions, you’ll need:

Thermometer
Hygrometer
Fans
Heaters or AC
Humidifiers or dehumidifiers

Best Temperature Ranges

Cannabis needs different temperatures at each growth stage. Here’s the breakdown:

Seedling Stage Temperatures

Keep temps between 70-85°F (21-29°C). This helps roots grow strong.

Pro tip: Use a heat mat if your room is cool.

Vegetative Stage Temperatures

Plants can handle slightly higher temps now:

Day: 70-85°F (21-29°C)
Night: 60-75°F (16-24°C)

This range helps leaves and stems grow well.

Flowering Stage Temperatures

Lower temps are best for flowering:

Day: 65-80°F (18-27°C)
Night: 60-75°F (16-24°C)

Cooler temps help buds grow and keep terpenes.

Late Flowering Stage Temperatures

Drop temps more in the final weeks:

Day: 64-75°F (18-24°C)
Night: 60-68°F (16-20°C)

This can boost resin and enhance colors.

Growth Stage	Day Temp	Night Temp
Seedling	70-85°F	65-80°F
Vegetative	70-85°F	60-75°F
Flowering	65-80°F	60-75°F
Late Flowering	64-75°F	60-68°F

Key takeaway: Lower temps as plants grow. This mimics nature and can lead to better yields and quality.

Best Humidity Levels

Humidity is key for cannabis growth. It affects how plants drink and eat. Here’s what you need to know:

Seedling Stage Humidity

Seedlings need high humidity (75-85%). This helps them drink and grow roots.

Tips:

Use a dome or plastic wrap for a mini-greenhouse
Mist seedlings 1-2 times daily
Put seedling trays on a heat mat

Vegetative Stage Humidity

Lower humidity to 45-55% as plants grow. This helps fast growth and fights mold.

How to manage:

Drop humidity 5% each week
Use fans for air flow
Check leaves – no water drops should form

Flowering Stage Humidity

Aim for 35-45% humidity. This prevents rot and boosts resin.

Tips:

Use a dehumidifier
Increase air flow, especially at night
Trim lower leaves for better air circulation

Late Flowering Stage Humidity

Drop to 30-40% in the last 2-3 weeks. This helps make denser, stronger buds.

How to control:

Keep using a dehumidifier
Water less often
Remove any dead leaves quickly

Growth Stage	Ideal Humidity
Seedling	75-85%
Vegetative	45-55%
Flowering	35-45%
Late Flowering	30-40%

Remember, these are guidelines. Some strains might like it a bit different, so watch your plants and adjust.

"Managing humidity right is crucial. It prevents mold and helps buds grow well. Don’t underestimate how it affects your yield and quality." – Chris McDonald, Happy Hydro

How Temperature and Humidity Work Together

Temperature and humidity are a team in cannabis growing. They’re linked through Vapor Pressure Deficit (VPD), which is key for plant health.

VPD measures the gap between the air’s moisture and how much it can hold. This drives transpiration – how plants move water and food.

Here’s how VPD affects cannabis:

Growth Stage	Ideal VPD (kPa)	What It Does
Vegetative	0.8 – 1.2	Boosts leaf growth and nutrient uptake
Flowering	1.2 – 1.6	Helps buds grow and produce resin
Late Flowering	1.0 – 1.3	Aids final bud ripening

Getting VPD right is crucial. Too low? You risk mold. Too high? Plants might dry out or get burned leaves.

To manage VPD:

Use good thermometers and hygrometers
Adjust temp and humidity for each growth stage
Use fans for air flow
Use humidifiers or dehumidifiers as needed

"Nailing temp and humidity is what makes a crop great, not just good." – Cannabis Expert

Remember, cannabis likes 70-85°F (21-29°C) during the day. Humidity needs change:

Seedlings: 65-70%
Vegetative: 40-60%
Early Flowering: 40-50%
Late Flowering: 30-40%

Common Questions About Growing Conditions

How Temperature Affects Yield

Temperature is huge for cannabis growth and yield. Plants love 70-85°F (21-29°C) during the day. Outside this range can hurt your crop:

Too hot: Slows growth, curls leaves, causes nutrient issues
Too cold: Stunts growth, can harm roots

Heat stress signs:

Curled or "taco" leaves
Brown leaf spots
Bleached or yellow tops

To max out yield:

Keep days around 75°F (24°C)
Let nights drop 10°F (6°C)
Use fans for air flow
Adjust grow lights as needed

Can High Humidity Cause Mold?

Yes, high humidity can lead to mold, especially when flowering. Risks go up when humidity tops:

70% in veg
60% in early flower
50% in late flower

To fight mold:

Use dehumidifiers in damp spots
Ensure good air flow with fans
Lower humidity as plants mature

Signs of Heat Stress in Cannabis

Watch for these:

Growth Stage	Heat Stress Signs
Seedlings	Slow growth, pale leaves
Vegetative	Curled leaves, burnt tips
Flowering	Bleached leaves, too many white hairs

If you see these, act fast to lower temps and prevent damage.

Adjusting Grow Room Temperature

To keep temps ideal:

Use thermometers to check often
Install good ventilation (air change every 4-5 minutes)
Consider AC for hot climates
Raise lights if temps spike
Use LED lights to reduce heat

Best Ways to Control Humidity

Effective humidity management:

Use hygrometers for accurate readings
Install dehumidifiers for high humidity
Add humidifiers in dry conditions
Adjust watering based on humidity
Seal and insulate grow room to stabilize conditions

"The biggest mistake new growers make is skimping on humidity control." – Gary Howard, Urban Garden Center

Tools for Temperature and Humidity Control

Growing cannabis needs precise temp and humidity control. Here’s what you need:

Temperature Control Equipment

HVAC Systems: Keep temps steady throughout your grow room.
Air Conditioners: Cool the space when it’s hot.
Heat Mats: Warm roots for seedlings and clones.

Humidity Control Tools

Dehumidifiers: Remove extra moisture from the air.
Humidifiers: Add moisture when it’s too dry.
Hygrometers: Measure humidity accurately.

Tool	What It Does	When to Use
HVAC	Controls temperature	All growth stages
Dehumidifier	Lowers humidity	Flowering stage
Humidifier	Raises humidity	Seedling/veg stages
Hygrometer	Checks humidity	All growth stages

Tips for Steady Conditions

Use Digital Controllers: Automate equipment to keep levels steady.
Install Fans: Improve air flow to prevent mold.
Check Often: Look at readings at least twice a day.
Change Slowly: Make small adjustments to avoid stressing plants.

"New growers often skimp on humidity control. That’s a big mistake." – Gary Howard, Urban Garden Center

For precise control, try the Extech 445713 hygro-thermometer. It’s accurate within +/- 1.8°F for temp and +/-5% for humidity, perfect for cannabis growing.

Fixing Temperature and Humidity Problems

Growing cannabis needs careful temp and humidity control. When issues pop up, act fast. Here’s how to tackle common problems:

Common Growing Problems

Many growers struggle with temp and humidity control. Overwatering is a big issue indoors, leading to high humidity and potential mold.

To fix this:

Water in the morning and evening to prevent fast evaporation
Use pots with good drainage
Check soil moisture often

Dealing with Extreme Temperatures

Heat stress can really hurt cannabis plants. Look for:

Pale, wilted seedlings
Dry leaves with curled edges
Yellow-brown leaf spots
Bleached or yellow leaves during flowering

To fight heat stress:

Use LED grow lights that make less heat
Keep roots cool by avoiding direct light
Ensure good air flow with fans that match your grow tent size

For example, Green Leaf Cultivators in Colorado faced a heatwave that pushed their grow room to 95°F. They installed a Vertical Air Solutions system and dropped temps by 12°F in 24 hours, saving their crop.

Managing Humidity Changes

Sudden humidity shifts can cause mold, pests, and poor nutrient uptake. Here’s how to manage:

Problem	Solution
High Humidity	Use a dehumidifier, improve air flow
Low Humidity	Add a humidifier, group plants together
Changing Levels	Install a humidity controller to automate

John Smith from CannaTech Solutions says: "We cut mold issues by 40% after adding 24-hour dehumidification to our HVAC system."

Conclusion

Growing great cannabis means keeping the right temp and humidity at each stage. Here’s what to remember:

Growth Stage	Temperature (°F)	Humidity (%)
Seedling	75-80	65-70
Vegetative	68-78	40-60
Flowering	65-75	35-45
Drying/Curing	60-70	45-55

Monitoring is key. Use digital thermometers and hygrometers. Many growers now use smart devices that alert their phones when conditions change.

Different climates need different approaches:

Northern California growers often need dehumidifiers
Las Vegas cultivators typically need humidifiers

Equipment like heaters, AC, humidifiers, and dehumidifiers help maintain ideal conditions. But it’s not just about having the right tools – it’s about using them well.

"Controlling your grow environment at all times is the single most important factor for successful harvests", says the Cannabis Cultivation Best Practices Guide.

Remember, genetics play a role in how plants handle different conditions. Some strains are tougher than others.

By watching and adjusting temp and humidity, growers can:

Prevent plant stress
Reduce mold and disease risk
Boost yield and quality

Stay alert and respond to your plants’ needs throughout their life cycle. With careful attention to environment, you’ll be on your way to a thriving cannabis crop.

FAQs

What is the best temperature and humidity for cannabis plants?

The best temp and humidity change as plants grow:

Growth Stage	Temperature (°F)	Humidity (%)
Seedling	70-85 (day)	75-85
	65-80 (night)
Vegetative	70-85 (day)	45-55
	60-75 (night)
Flowering	65-84 (day)	35-45
	60-75 (night)

Watch these ranges and adjust as needed for best results.

How do you climate control a grow room?

To control grow room climate:

Use HVAC or AC for temperature
Install dehumidifiers or humidifiers for humidity
Set up fans for air flow
Use heat pumps or heating pipes with heated/chilled water

Choose tools that fit your space and budget. The goal is steady conditions.

Is 60% humidity too high for cannabis?

For most growth stages, 60% humidity isn’t too high. But it depends on the plant’s age:

Seedlings like 65-70% humidity
Vegetative plants do well with 40-60%
Flowering plants need 35-45%

During flowering, 60% humidity can be risky. It might cause mold or mildew. To be safe, aim for 40-50% humidity when plants are flowering. This prevents issues while keeping plants happy.