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What happens if your grow room is too hot?

Tom Starley
January 11, 2024
12 min read
A man checks the temperature of his grow room.
A man checks the temperature of his grow room.
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Maintaining the right environment is crucial for flourishing plants when you grow cannabis indoors. One key aspect of this environment is temperature. 

Ideal temperatures in your grow room can be the difference between lush, healthy plants and a disappointing harvest. This post delves into a common yet critical question many growers ask: what happens if your grow room gets too hot?

Understanding the ideal temperatures

Before we dive into the problems caused by excessive temperatures, it's important to understand what we mean by the 'ideal' temperature. 

Generally, most plants thrive in a temperature range between 20°C to 25°C during the day when the lights are on. It's a bit cooler at night, but not by much. However, this can vary.

This ideal depends on a few variables, including the strain your growing, what lights you’re using, if you’re supplementing with CO2 and the plants stage of growth.

For example, cannabis plants have specific temperature needs that change during their lifecycle. 

Seedlings, young plants and those in the vegetative stage prefer it a bit warmer, while mature plants can handle slightly higher temperatures, especially during the first 3 to 4 weeks of the flowering stage.

This intricate balance of temperature control is more than just setting a thermostat. It involves understanding your plants' needs, the stage of their growth, and how factors like humidity and light interact with temperature.

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Signs your grow room is too hot

It's vital for any grower to recognise the early signs of too much heat in a grow room. This can save your plants from long-term damage. Here are some key indicators:

Cannabis leaves curling up due to the grow room temperature being to hot.

Wilting leaves.
This is often the first of the visible signs. If your plant's leaves are drooping or curling up, they might be trying to reduce their surface area to conserve water and reduce heat absorption due to excess grow tent heat and high Vapour pressure deficit (VPD).

Dry soil. If the soil is drying out quicker than usual, it's a sign that ambient temperatures are too high and or that your VPD is too high.

Yellowing or brown spots on leaves. Hot temperatures and heat stress can cause leaves to develop yellow or brown spots, a sign that they're burning. This is especially the case if your plants are too close to a hot light source like a HPS (High-Pressure Sodium) grow light.

Slowed growth. If your plants aren't growing as quickly as they should be, or if plants in the flowering stage stop developing new buds, too much heat could be the culprit. 

In the bulking phase of the flowering cycle, weeks 3 to 6, it’s essential to mimic autumn conditions and slightly lower temperatures to preserve terpene profiles. 

Monitoring temperature effectively

To ensure you're keeping a close eye on your environment and maintaining the right conditions:

  • Use reliable Grow Sensors, thermometers or hygrometers to monitor the temperature and humidity levels in your grow tent or space.
  • Place them at different heights and locations within the grow room, as heat rises and temperature can vary in different spots.
  • Regularly check your grow tent heat readings, especially during hot spells or changes in your grow room setup.

An image showing the best place to hang your Grow Sensor to get an accurate temperature reading.

High temperatures and relative humidity

It's not just about the thermometer reading. High temperatures often come with low relative humidity, which can further stress your plants as a result of your VPD being too high

Indoor cannabis plants, for instance, need more moisture and higher humidity during their vegetative stage and lower humidity during flowering. Balancing these environmental factors is critical to maintaining a healthy environment to grow healthy plants.

A thermometer next to a cannabis plant showing that the temperature is to hot in the grow room.

Impacts on plant health and growth

The toll of high temperatures on plants

When your grow room experiences higher temperatures, it doesn't just cause immediate discomfort to your plants; it triggers a series of stress responses that can significantly hinder their growth and health. Here's how excessive heat impacts your plants:

Stress and poor growth. Plants under heat stress expend more energy trying to survive, which can severely limit their growth. This is especially true for young plants and seedlings, which are more vulnerable to temperature fluctuations and tent temperature. 

Advanced growers can use plant stress to manipulate how a plant grows, but too much stress in any direction will provide negative results. 

Nutrient burn and dehydration. High temperatures in your grow tent can accelerate the uptake of nutrients and water, leading to nutrient burn

This happens when plants absorb more nutrients than they can process, resulting in burnt leaf tips and edges where the leaves turn brown. Additionally, excessive evaporation can lead to dehydration, further stressing the plants. 

Top tip: you can use VPD to control how much nutrients a plant will take up. Lower your VPD slightly if you see signs of over-feeding.

Stunted growth and reduced yield. Long periods of high temperature can stunt plant growth. For flowering plants like cannabis, this can mean smaller bud growth and a reduced yield, significantly impacting your harvest's overall quality and quantity.

Vulnerability to pests and diseases. Stress from high grow tent temperatures can weaken your plants’ natural defences, making them more susceptible to pests and diseases

This could lead to a higher risk of issues like spider mites or fungal infections, which thrive in hot, dry conditions. And no one wants that!

Root rot in high temperatures. Another often-overlooked impact of high grow tent temperatures is root rot. However this is more of an issue for hydroponic growers using DWC systems.

This occurs when the temperature of the nutrient solution becomes too warm, fostering harmful bacteria growth at the plants’ roots. Healthy roots are crucial for plant health; root rot can quickly devastate your entire crop.

Adapting to rising temperatures. Adapting your grow room practices is essential in the face of rising temperatures. This might include adjusting your watering schedule, changing the nutrient concentration, or altering the grow light schedule to reduce heat.

Remember, each plant has its unique tolerance levels, and what works for one might not work for another.

A wilting cannabis plant in a grow room that is to hot.

Long-term consequences of heat stress

The effects of high temperatures in a grow room when growing cannabis can extend far beyond the immediate growing cycle. Here's what long-term overheating can do:

Irreversible plant damage

Prolonged exposure to excessive heat can cause irreversible damage to the plants' cellular structure. This affects the current yield, plants' future growth potential, and reproductive capabilities.

Decreased quality and yield

Over time, consistent heat stress can significantly decrease your harvest's quality and quantity. 

In cannabis cultivation, for example, this could mean less potent buds with a lower concentration of cannabinoids and terpenes. 

The focus should always be on quality. Usually, higher yields will follow.

Altered plant characteristics

High temperatures can alter the physical characteristics of plants, leading to unusual growth patterns, discoloured leaves, and, in some cases, the development of hermaphroditic traits, especially in cannabis plants. 

Be on the lookout for male pollen sacks or bananas. These guys can fertilise your grow room if not removed.   

Spider mites on a cannabis plant that is in a to hot enviroment.

Impact on the ambient environment

The long-term effects of excessive heat when you grow indoors aren’t limited to the plants themselves. Here's how it can affect the grow room environment:

Creating a breeding ground for pests and diseases

Consistently high temperatures can create a perfect breeding ground for pests and diseases. These problems can become entrenched in your grow space, making them harder to eradicate over time. 

Pests like spider mites love warm environments. It also increases their reproduction rate, compounding the problem.

Compromised equipment efficiency

A prolonged hot spell in your grow tent can also take a toll on your equipment. For instance, fans and air conditioners might have to work harder to maintain cooler temperatures, leading to quicker wear and tear.

Managing heat for long-term success

To avoid these long-term consequences, it's crucial to implement effective heat management strategies. 

This involves cooling down your grow room when it gets too hot and maintaining stable temperatures throughout your plants' growth cycles.

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Managing heat: prevention and solutions

Strategies for keeping your grow room cool

Preventing overheating is key to maintaining a healthy grow room. Here are some effective strategies:

Grow at the right time of the year

Depending on your location and growing style, you can use the ambient weather to your advantage. Flowering in autumn, winter and spring allows you to make use of cool outside air to control the temperature.

Adequate ventilation

Good ventilation is crucial. Ensure your grow tent has a well-designed air exchange system (if you’re not supplementing your room with CO2). Use an exhaust system to remove hot air and intake fans to bring in cool air. 

Exhaust fans also help to remove stagnant air and maintain optimal levels of carbon dioxide, which is essential for plant growth.

Air conditioning and cooling systems

Especially in warmer climates, many growers find that air conditioners are necessary to maintain optimal grow space temperatures. Investing in a reliable air conditioning system can be a game-changer for controlling tent heat.

Consider using a sealed room

Although there is an upfront cost, supplementing your space with CO2 in a sealed environment allows you to reduce cooling costs in the summer months. As you’re only cooling the air in your space.

Utilise oscillating fans

These fans help circulate air within the grow room, preventing hot air pockets and providing a gentle breeze that strengthens plant stems.

Increase air circulation

Sometimes, simply improving air circulation can significantly cool down a grow room. This can be achieved by repositioning fans or adding more if necessary.

Use of water chillers

For hydroponic systems, water chillers can keep nutrient solutions at an optimal temperature, thereby reducing the overall temperature of the grow room.

Shade cloths and reflective materials

Using shade cloths or reflective materials on windows and walls can reduce the amount of heat entering the grow room.

It’s crucial to measure how effectively your strategies temperature management strategies are working. That’s why we created the Grow Sensor.

The Grow Sensor is placed within your grow room to monitor and provide feedback on environmental conditions. This data is invaluable for making informed improvements to your grow space.

Understanding the precise environmental conditions your plants are experiencing is essential. Without this knowledge, optimising your grow room, controlling your temperature and ensuring the best possible growth becomes challenging.

The primary motivation for indoor cultivation is to have absolute control over the growing environment. However, if you neglect to track and analyse data, you’ll be missing out on better-quality flower, evolved terpene profiles and higher yields.

The Grow Sensor and app.

Reducing heat sources

Adjusting your grow light schedule

Grow lights are a major heat source in grow rooms. Adjusting to having lights on during cooler parts of the day and off during the hottest can help manage temperatures.

Switch to an LED grow light

Consider switching to LED grow lights if you're using high-intensity discharge (HID) lights that emit more heat. LEDs emit less heat and are more energy-efficient.

If you're really struggling with heat, the coolest running grow lights are blurple LEDs, these are the most efficient as they don’t include the full spectrum of light. 

A tomato plant under a led grow light.

Regular monitoring and adjustments

Constant vigilance is key in a grow tents. Regularly check temperature and humidity levels, and be prepared to adjust your cooling strategies as needed. 

Remember, what works in one season might not be effective in another.

Illustrative examples

Overcoming high temperatures in a commercial cannabis facility

In a large-scale cannabis facility located in Southern California, the management faced significant challenges during a summer heatwave. 

Temperatures in the grow rooms soared above 34°C, leading to heat stress and slowed growth in their plants.

Solution Implemented:

  • Upgraded to a more robust HVAC system.
  • Installed additional oscillating fans for better air circulation.
  • Adjusted the light schedule to avoid the hottest parts of the day.
  • Implemented a more frequent watering schedule to combat dehydration.
  • Introduced multiple Grow Sensors to monitor the spread of the environment across the space.


Post these changes, the facility reported a noticeable improvement in plant health and reduced heat-related stress. The facility was able to increase yields and saw higher potency and better bud structure.

An air-conditioning uint in a greenhouse.

Small-scale grower tackles overheating issue

A hobbyist grower in the UK experienced persistent problems with high temperatures in his grow tent, especially during the flowering stage of his cannabis plants. The confined space of the tent made temperature management particularly challenging.

Solution Implemented:

  • Switched from HIDs emitting more heat to LED grow lights to reduce grow light heat output.
  • Installed a small air conditioning unit specifically for the grow tent.
  • Used a digital thermostat to closely monitor and adjust the temperature.
  • Installed a Grow Sensor to monitor the environment 24/7.


These changes resulted in a more stable grow environment. The grower observed improved plant health, less heat stress, and a more successful flowering phase, ultimately leading to a better-quality harvest.

Addressing root rot in a hydroponic setup

In an indoor hydroponic system, a grower faced issues with root rot, which were traced back to high nutrient solution temperatures.

Solution Implemented:

  • Installed a water chiller to maintain the nutrient solution at ideal temperatures.
  • Increased air stone activity to boost oxygen levels in the water.
  • Regularly monitored water temperatures and adjusted the chiller settings as needed.


The water chiller's introduction successfully controlled the nutrient solution's temperatures, leading to healthier root systems and overall plant health. The grower saw a decrease in rot occurrences and an increase in yield.

A man pointing a IR heat gun at a cannabis plant.

Case studies

Here are some key studies highlighting the impact of temperatures on plant health and growth in controlled environments like grow rooms. Here are some insights from the research:

Temperature and crop quality

Research has shown that temperatures, in combination with light, significantly affect crop quality attributes such as branching, stem thickness, flower number, and flower size.

This is particularly noticeable in certain cold-tolerant plants like Dianthus, French marigold, and petunia, where lower temperatures can improve plant quality but also prolong flowering time. 

Conversely, optimal flower size and quality are achieved at moderate temperatures, around 68°F (20°C) for cold-sensitive species. 

However, once the average temperature exceeds 70°F (21°C), overall crop quality declines, emphasising the need for temperature control in grow rooms​​. 

Effects of temperature on plants

Another study highlights the wide range of temperatures that plants experience throughout their life cycle. 

This research underscores the importance of temperature adaptation in plants and the need for continuous adjustment to variable temperature conditions. 

It emphasises that plants must adapt to seasonal changes and daily temperature fluctuations, which can sometimes exceed 15°C in a single day​​. 

These studies underline that temperature management is crucial not just for plant survival but also for ensuring the best possible growth and yield quality.


In indoor growing, precision and care are paramount. Temperature control in your grow room is a fundamental factor that can make or break your success. 

The consequences of high grow room temperatures can be far-reaching, affecting not only your plants' immediate health and growth but also your harvest's long-term quality and yield.

From the early signs of wilting leaves and dry soil to the intricate interplay of temperatures, light, and plant quality, it's clear that maintaining the right temperature isn't a one-size-fits-all solution. 

Different plants have different needs; as a grower, you must understand and meet those needs.

We've seen how overheating can lead to nutrient burn, dehydration, and stunted growth. It can stress your plants, making them vulnerable to pests and diseases, and even alter their physical characteristics. 

Root rot, a silent threat, can quietly devastate your crop if the nutrient solution temperature isn't carefully managed.

But it's not all doom and gloom. You can prevent overheating in your grow room with the right strategies and monitoring equipment. 

Adequate ventilation, air conditioning, and thoughtful lighting schedules can all contribute to a healthier grow environment. 

Real-life case studies have shown us that growers, both large and small-scale, have successfully tackled overheating challenges with creative solutions.

In conclusion, the temperature in your grow room is a critical variable that requires your attention and diligence. 

By understanding the unique needs of your plants, monitoring temperature and humidity levels, and implementing effective cooling strategies, you can ensure that your plants thrive, producing healthy, vibrant, and bountiful yields.

Happy growing.

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Tom Starley
January 11, 2024
12 min read

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