Summer can become one of the most challenging periods for keeping an indoor cultivation environment stable. When the outdoor temperature rises, it also becomes more difficult to remove the heat generated by lighting, electrical equipment and the plants themselves. Controlling excess heat in indoor cannabis cultivation helps maintain a more stable environment and reduce problems related to heat stress, dehydration, irregular humidity and slower development.
This article from the Hydroponics Blanes Blog is for informational purposes only. At Hydroponics Blanes, WE DO NOT sell marijuana containing THC. In our physical shop and at growshopweb.com, we offer everything needed for self-cultivation, including fertilizers, nutrients, substrates, irrigation systems, fans, extractors, environmental controllers and indoor grow lighting systems.
Why is heat a problem in indoor cultivation?
One of the main advantages of indoor cultivation is the ability to control a large part of the environmental conditions. However, during the summer months, this control requires more attention. High outdoor temperatures make it more difficult to remove heat and can cause a grow tent or cultivation room to reach excessively high temperatures, even when an extraction system is in place.
The temperature in indoor cannabis cultivation depends on several factors: the temperature of the air entering the room, lighting power, size of the space, extractor airflow, number of plants, relative humidity and the amount of electrical equipment operating inside the area.
As a general reference, an approximate range between 20 and 28 °C is suitable for many indoor cultivation situations. When the temperature remains close to or above 30 °C for prolonged periods, signs of heat stress in cannabis may begin to appear.
Main symptoms of heat stress
Heat problems in cannabis cultivation do not always appear suddenly. They often begin with small changes in the leaves and water consumption.
- Leaves with raised or curled edges.
- Drooping appearance during the hottest hours.
- Faster evaporation of water from the substrate.
- Need for more frequent watering.
- Slower growth.
- Greater difficulty maintaining stable relative humidity.
- Appearance of particularly hot areas near the grow lights.
- Increased activity of certain pests favored by hot and dry environments.
- Problems with balanced nutrient uptake when heat stress continues for too long.
Ideal temperature for cannabis cultivation in summer
Talking about the ideal temperature for cannabis cultivation does not mean aiming for exactly the same value throughout the entire day. The main objective is to avoid extreme fluctuations and maintain a reasonably stable environment.
During the lighting period, temperatures approximately between 22 and 28 °C are generally manageable when there is good air circulation. During the dark period, a moderate drop may occur. Problems arise when the temperature remains too high for many hours or when there are significant differences between different areas of the cultivation space.
For this reason, measuring temperature only next to a wall may provide an unrepresentative reading. It is advisable to place the sensor approximately at plant height and away from the direct airflow of a fan.
How to lower the temperature in indoor cultivation
There is no single solution for lowering the temperature in indoor cultivation. The best results are generally achieved by combining extraction, air intake, internal air circulation, efficient lighting and automatic control.
The image accompanying this article shows a very useful basic setup: fresh air entering from the lower area, horizontal air movement using fans and hot air extraction from the upper section. Hot air tends to accumulate at the top, so positioning the exhaust outlet higher up makes heat removal easier.
Improve air extraction
Extraction is one of the most important elements for combating heat. A properly sized extractor removes hot air and allows cooler air to enter from outside the grow tent or room.
For medium-sized installations, for example, the RVK 150 mm. L1 700 m3/h Extractor by RVK can be used and is available from Hydroponics Blanes. This model provides a high airflow rate and can be integrated with ducting, filters and speed controllers.
For spaces requiring even greater capacity, the RVK 200 mm. A1 700 m3/h Extractor by RVK is also available. The choice between different models should take into account the volume of the space, duct length, duct diameter, presence of a carbon filter and the amount of heat that needs to be removed.
Fresh air intake from the lower area
Powerful extraction requires an adequate air intake. When the extractor removes air but the intake openings are too small, actual airflow is significantly reduced.
In small grow tents, a correctly sized passive intake may be sufficient. In installations where air renewal needs to be reinforced, an inline intake fan can be used, such as the InLine Extractor 150 mm. Vanguard, with a stated airflow of 305 m3/h.
The intake should preferably be located in the lower section and the extraction point in the upper section. This arrangement takes advantage of the natural movement of hot air and improves temperature control in indoor cultivation.
Ventilation in indoor cannabis cultivation
Extraction and internal ventilation perform different functions. The extractor renews the air in the room, while internal fans keep the air moving around the plants.
Proper ventilation in indoor cannabis cultivation helps prevent pockets of hot air, especially beneath grow lights, in corners and between groups of plants.
Oscillating fans
For grow tents and small spaces, the CYCLONE 20 cm Oscillating Clip Fan can be a practical option. The unit has two speeds and 180° oscillation, allowing air movement to be distributed over a wide area without taking up floor space.
In larger rooms, the CYCLONE 40 cm Wall Fan with remote control can be used. This model offers three speeds, 90° oscillation and wall mounting, making it especially practical when a large amount of air needs to be moved without reducing the available space around the plants.
Lower-level circulation can also be complemented with the CYCLONE 20 cm Floor Fan, directing the airflow beneath the plant canopy to prevent stagnant areas.
It is not advisable to direct an extremely strong airflow continuously toward a single plant. The goal is to maintain distributed and constant air movement.
How to cool an indoor cultivation area using LED lighting
A significant part of the heat in indoor cultivation comes from lighting. HPS systems and other traditional technologies convert a considerable amount of electrical energy into heat.
One of the most effective strategies for cooling an indoor cultivation area is to use efficient LED lighting. An LED system still produces heat, but it can generate a high amount of usable light with lower energy consumption than many traditional technologies.
At growshopweb.com there is a wide range of LED systems for indoor cultivation, including fixtures and bars from specialist brands. Choosing an efficient grow light can make environmental control considerably easier during summer.
Adjust power when possible
Many modern LED systems allow power adjustment. During particularly hot days, it may be useful to operate at a slightly lower intensity when environmental conditions exceed the desired values.
It is also advisable to check the distance between the lights and the tops of the plants. A distance that is too short can create hot spots even when the average room temperature appears to be correct.
Changing the lighting schedule during summer
A simple strategy for cannabis cultivation in summer is to schedule the lighting period during the night, when outdoor temperatures are usually lower.
Instead of keeping the lights on during the hottest hours of the day, the light cycle can be organized to take advantage of cooler nighttime conditions. This allows the extractor to draw in cooler outside air and reduces the amount of work required to keep the environment within the desired range.
This change does not completely eliminate the problem when nights remain very hot, but it can reduce the maximum temperature inside the cultivation area by several degrees.
Automatic temperature and ventilation controllers
Manually checking the temperature several times a day can be impractical. Climate controllers make it possible to automate part of the process and adjust extraction speed according to environmental conditions.
Among the products available at Hydroponics Blanes is the CAN-FAN Fan Controller CAN EC Speed and Temperature. This controller allows a target temperature to be set and compatible EC extractors to be managed, helping to maintain more stable ventilation.
Another more complete option is the CAN-FAN Fan Controller LCD CAN FAN EC Humidity, designed to manage temperature and humidity through an LCD screen while also allowing minimum and maximum speed adjustments.
Automating temperature control in indoor cultivation reduces dependence on constant manual adjustments and allows a faster response when temperatures rise.
When should air conditioning be used?
Extraction can only bring the indoor temperature closer to the temperature of the incoming air. If the outdoor temperature is 32 or 34 °C, continually increasing the extraction rate is unlikely to keep the indoor area at 25 °C.
In these situations, air conditioning may become the most effective solution. The system should be sized according to the volume of the room and, especially, the heat load generated by lighting and electrical equipment.
It is advisable to avoid directing cold airflow directly at the plants. A better option is to cool the air in the room and allow fans and extractors to distribute the temperature evenly.
Humidity control during hot days
Temperature and humidity are directly related. As temperature increases, relative humidity may decrease even if the actual amount of water vapor remains almost unchanged.
After watering, the opposite can happen: evaporation increases and humidity spikes may appear, especially in small spaces.
For this reason, it is advisable to use a thermo-hygrometer with maximum and minimum temperature and humidity recording. These readings make it possible to check what happens during the hours when nobody is monitoring the cultivation area.
Evaporative coolers
Evaporative coolers can reduce temperature through water evaporation, but they also increase ambient humidity. They work best in dry climates and require greater caution when humidity is already high.
Before using this type of system, it is advisable to measure temperature and humidity together. Lowering the temperature by several degrees is not beneficial if humidity rises to levels that are difficult to control.
Watering and high temperatures
During a heatwave, the substrate can lose moisture much more quickly. However, this does not mean it should remain constantly saturated.
It is better to observe the weight of the pot, substrate moisture and the plants’ response before changing the watering schedule. Overwatering can reduce the oxygen available around the roots, while allowing the substrate to dry too much adds further stress.
Whenever possible, watering can be carried out at the beginning of the lighting period, avoiding large amounts of water immediately before the dark period.
Avoiding hot spots inside the grow tent
The temperature indicated by a single sensor does not always represent the entire cultivation area. Significant differences may exist between the lower section, central area and the space directly beneath the grow lights.
To detect hot spots, it is advisable to:
- Measure the temperature at several points.
- Pay particular attention to the upper part of the plants.
- Keep air inlets and outlets unobstructed.
- Avoid accumulations of cables and electrical equipment inside the grow tent.
- Position fans to create cross-ventilation.
- Regularly clean grilles, filters and fan blades.
- Check that ducting does not contain unnecessary bends.
Insulating the cultivation space
When a room receives direct sunlight for many hours, the temperature can rise even before the grow lights are switched on.
Proper insulation of walls, ceilings and windows helps limit the amount of heat entering from outside. Suitable insulating materials can reduce heat transfer and make extraction or air conditioning more effective.
It is also advisable to check where hot air is being discharged. Releasing it into the same room from which fresh air is drawn creates a closed loop that progressively raises the temperature.
Recommended products for combating summer heat
To prepare an indoor cultivation area for high temperatures, at Hydroponics Blanes we recommend combining several elements depending on the size of the installation:
- RVK 150 mm. L1 700 m3/h Extractor – RVK: suitable for renewing large volumes of air in medium-sized installations.
- RVK 200 mm. A1 700 m3/h Extractor – RVK: an alternative with a 200 mm connection for compatible ventilation systems.
- InLine 150 mm. Extractor – Vanguard: useful as support for air intake or air movement through ducting.
- 20 cm Oscillating Clip Fan – CYCLONE: recommended for air recirculation in grow tents.
- 40 cm Wall Fan with remote control – CYCLONE: suitable for rooms where wider air circulation is required.
- 20 cm Floor Fan – CYCLONE: helps move air through the lower part of the cultivation area.
- Fan Controller CAN EC Speed and Temperature – CAN-FAN: allows compatible EC extractors to be automatically regulated.
- Fan Controller LCD CAN FAN EC Humidity – CAN-FAN: allows temperature, humidity and ventilation speeds to be controlled.
- LED systems for indoor cultivation: help reduce heat load compared with certain traditional lighting technologies.
- Thermo-hygrometers: essential for monitoring maximum and minimum temperatures and humidity levels throughout the day.
Before choosing an extractor or controller, it is advisable to calculate the volume of the grow tent or room and take into account filters, ducting, bends and lighting power. An extractor that is too small may become insufficient during summer, whereas a properly sized system can maintain much more stable conditions.
Common mistakes when dealing with heat in indoor cultivation
Some problems arise not because of a lack of equipment, but because of incorrect setup. Some of the most common mistakes include:
- Using only internal fans without proper extraction.
- Drawing fresh air from a room that is already too hot.
- Exhausting hot air back into the same room.
- Installing a filter that is too restrictive for the extractor being used.
- Using very long ducting or too many bends.
- Positioning extraction at the bottom of the space.
- Keeping grow lights too close to the plants.
- Running the lighting during the hottest hours of the day.
- Not measuring temperature during the dark period.
- Confusing internal ventilation with air renewal.
How to prepare an indoor cultivation area before a heatwave
The best way to deal with extreme temperatures is to prepare the installation before the hottest period arrives. Waiting until the grow tent reaches excessive temperatures considerably limits the available options.
Before summer, it is advisable to check the operation of extractors and fans, clean filters and grilles, check environmental sensors, review the lighting schedule and make sure that hot air can be discharged outside the room.
It is also useful to monitor outdoor temperatures for several days. When the air entering the cultivation area is already too hot, it may be necessary to supplement extraction with air conditioning.
A combined strategy for keeping cultivation conditions stable
Combating excess heat in indoor cannabis cultivation requires looking at the space as a complete system. Installing a powerful fan is not enough if the hot air remains inside the room, and continually increasing extraction will not help when the outside air is already too warm.
An effective setup combines fresh air intake in the lower area, high-level extraction, internal fans, efficient lighting, correctly positioned sensors and automatic control when necessary.
During cannabis cultivation in summer, small changes such as moving the lighting schedule to nighttime, improving the ducting layout or adding airflow to a stagnant area can significantly reduce temperature peaks.
At Hydroponics Blanes you will find extractors, fans, climate controllers, LED systems, fertilizers, nutrients, measuring equipment and other products intended for self-cultivation. A properly sized installation makes it easier to cope with summer conditions and maintain a more stable environment throughout the year.