Cannabis Vanguard — innovation & science by Excellent Nutrient
Indoor Climate and Plant Physiology: The Limiting Factor Nobody Controls Well in Summer
Summer exposes the weaknesses of any undersized climate control system. Outdoor temperatures rise. Relative humidity increases in coastal areas. Energy consumption shoots up.
In these conditions, indoor climate control becomes the limiting factor in production. However, many growers still manage these parameters intuitively and without technical criteria.
In professional indoor cannabis cultivation, climate is not a secondary parameter. Indeed, it is the variable that determines whether the lighting programme, nutrition and genetics express their maximum potential.
Furthermore, temperature, humidity, CO₂ and VPD are four interdependent parameters. They must be managed in an integrated manner. Therefore, optimising one without considering the others generates physiological imbalances that reduce yield and final quality.
Temperature in Cannabis: Optimal Ranges and Summer Management
Temperature is the environmental parameter with the greatest impact on metabolic processes in cannabis. Each enzyme involved in photosynthesis has an optimal temperature range. Outside that range, its activity drops drastically.
Vegetative phase: The optimal range is 22 to 28°C during the light photoperiod. Below 18°C growth slows significantly. Above 30°C photosynthetic activity begins to decline.
Flowering phase: The optimal range is 20 to 26°C during the light period. Thermal tolerance is lower in flowering than in vegetative. Temperatures above 28°C for more than 4 consecutive hours accelerate the degradation of THCA to CBN. Furthermore, they reduce trichome density notably.
Dark period: The recommended range is 16 to 20°C. The thermal differential between light and dark periods is called DIF. A moderate positive DIF of 4 to 6°C favours compact internodes and greater inflorescence density.
Summer management: In installations with high LED light loads, heat generated adds 2 to 5°C to ambient temperature. In Mediterranean areas, outdoor temperatures can exceed 35°C in summer. Therefore, the sizing of the cooling system is critical. Direct expansion systems with a COP above 3.5 are the reference solution for continuous production installations.
Relative Humidity and VPD: The Most Underestimated Parameter in Professional Cannabis
VPD, or Vapour Pressure Deficit, is the difference between the vapour pressure the air can hold and the vapour pressure it actually contains. It is the parameter that determines the force with which the plant transpires. Therefore, it directly regulates the speed of water and nutrient absorption from the rhizosphere.
A low VPD, with high relative humidity, reduces transpiration. This limits nutrient flow to aerial tissues. However, a high VPD forces excessive transpiration. As a result, this can generate water stress even with moist substrate.
Optimal VPD ranges by phase:
In cuttings and rooting the range is 0.4 to 0.8 kPa. Relative humidity must be maintained between 70 and 80%. This minimises transpiration in plants without an established root system.
In the vegetative phase the range is 0.8 to 1.2 kPa. Optimal relative humidity is 55 to 70%. Furthermore, this balance optimises active transpiration and efficient root absorption.
In early flowering the range is 1.0 to 1.4 kPa. Relative humidity should drop to 50 or 60%. Additionally, progressive reduction begins to stimulate nutrient flow towards developing inflorescences.
In full and late flowering the range is 1.2 to 1.6 kPa. Relative humidity should be between 40 and 50%. This reduction is critical to prevent the development of Botrytis cinerea. Indeed, it is the most destructive pathogen in cannabis flowering.
In final maturation relative humidity should drop below 40%. This extreme humidity reduction stimulates resin production as the plant’s defensive response.
CO₂: Enrichment, Physiology and Supplementation Protocol
Carbon dioxide is the substrate of photosynthesis. Under normal atmospheric conditions, approximately 420 ppm in 2026, CO₂ is frequently the limiting factor of photosynthetic rate. This occurs especially in high light density crops.
CO₂ supplementation in indoor installations allows concentration to be raised to 800 or 1500 ppm. Moreover, documented effects include higher photosynthetic rate, faster growth and better final yield.
At 800 to 1000 ppm, the net photosynthetic rate can increase by 20 to 30%. However, this only occurs when temperature, VPD and PPFD are within optimal ranges. At 1200 to 1500 ppm, the increase can reach 40 to 50% in high-response cultivars.
Furthermore, with elevated CO₂ plants tolerate temperatures of up to 28 to 30°C without loss of photosynthetic efficiency. This is especially relevant in summer, when cooling is not always sufficient.
Supplementation protocol:
CO₂ supplementation only makes sense when PPFD exceeds 600 µmol per square metre per second. Below that threshold, the plant cannot utilise additional CO₂. Additionally, CO₂ must be injected during the light period and distributed homogeneously above the canopy. During the dark period supplementation must cease completely.
To optimize crop performance, it is essential to apply advanced plant nutrition strategies that complement the climate control programme throughout each phase of the growth cycle.
Climate Integration: Automated Environmental Control Systems
Manual management of climate parameters is unviable in continuous production installations. The variability between manual readings and delays in correcting deviations generate cumulative productive losses. Therefore, environmental control automation is essential.
Integrated environmental control systems combine several key components. First, temperature, humidity and CO₂ sensors distributed at multiple points in the chamber. Furthermore, PID controllers adjust the response of climate equipment based on detected deviations. Finally, predictive control algorithms anticipate thermal load changes associated with lighting cycles.
Multivariable climate controllers: Platforms such as Argus, Priva or TrolMaster allow the programming of complete climate recipes. These recipes automatically vary temperature, humidity and CO₂ setpoints according to the cycle phase. Moreover, integration with the lighting system coordinates the start of the light period with CO₂ activation.
Leaf temperature sensors: Infrared thermometers allow monitoring of actual leaf temperature. This is the relevant parameter for VPD calculation, not air temperature.
Active dehumidification systems: In summer, the combination of high temperature and high plant transpiration generates humidity peaks. Dehumidifiers with capacities of 50 to 200 litres per hour are critical components in Mediterranean installations during summer months.
Most Frequent Climate Errors in Summer and How to Avoid Them
Summer amplifies any weakness in the climate control system. However, the most frequent errors are perfectly avoidable with an adequate protocol.
Night temperature too high: In summer, cooling systems work at their limit during the light period. Furthermore, they often fail to recover the target temperature during the dark period. Night temperatures above 22°C accelerate plant respiration. As a result, carbohydrate reserves accumulated during the day are consumed and final yield is reduced.
High relative humidity in late flowering: The combination of high temperature and humidity above 55% in the final weeks of flowering creates ideal conditions for Botrytis development. Indeed, a single week of favourable conditions can destroy an entire harvest. Therefore, continuous humidity monitoring is essential.
Absence of air circulation: Air movement within the chamber is as important as temperature and humidity. Active circulation homogenises temperature and CO₂ concentration. Moreover, it makes it difficult for fungal pathogens to establish. Air velocities of 0.3 to 0.5 metres per second at canopy level are the target in professional installations.
CO₂ supplementation without temperature control: Raising CO₂ without simultaneously managing temperature generates a physiological paradox. The plant increases its photosynthetic rate but also its leaf temperature. Consequently, this can lead to heat stress if cooling is insufficient. Therefore, CO₂ and temperature must always be managed in an integrated manner.
Climate Control as a Competitive Advantage in Professional Cannabis Production
The professional cannabis market is evolving towards increasingly demanding quality standards. Institutional buyers and operators demand products with consistent and reproducible cannabinoid and terpene profiles. Therefore, climate variability within the installation is today a commercial problem, not only an agronomic one.
A well-designed climate control system reduces variability between cycles. Furthermore, it improves homogeneity between plants within the same chamber. As a result, the final product has greater analytical consistency and higher commercial value.
The investment in professional climate control has a clear and measurable economic return. First, it reduces losses from Botrytis and other pathogens favoured by inadequate climate conditions. Moreover, it maximises the genetic expression of each cultivar. Therefore, yield and quality increase simultaneously.
Digitalisation and Remote Climate Monitoring in Cannabis
The digitalisation of climate control is the next frontier in professional cannabis production. Current systems allow monitoring of all environmental parameters in real time from any mobile device. Furthermore, they generate automatic alerts when any parameter deviates from the programmed range.
This remote monitoring capability is especially valuable in summer. Temperature and humidity deviations occur more frequently and rapidly during warm months. However, with an active alert system, the grower can correct any deviation in minutes, even without being physically present in the installation.
The historical data generated by these systems also has enormous agronomic value. Indeed, it allows identification of climate deviation patterns associated with specific cycle phases. Furthermore, it facilitates progressive optimisation of climate recipes cycle by cycle.
The integration of CO₂ sensors, leaf temperature sensors and high-precision hygrometers with cloud management platforms represents today the reference standard in continuous production installations. Therefore, any installation aspiring to compete in the professional market must incorporate this technology as part of its basic infrastructure.
Weekly Climate Review Protocol in Summer
Summer demands more frequent climate attention than the rest of the year. Therefore, it is advisable to establish a weekly climate review protocol during the months of June to September.
This protocol must include verification of the maximum and minimum temperature ranges recorded during the week. Furthermore, it must review relative humidity peaks in the densest canopy zones. Additionally, it is essential to check the average CO₂ concentration during the light period and verify that VPD remains within the programmed range for each phase.
Moreover, it is advisable to check the condition of climate system filters every two weeks in summer. Blocked filters progressively reduce cooling and dehumidification capacity. As a result, the installation loses climate efficiency precisely when it needs it most.
Finally, periodic calibration of temperature and humidity sensors is essential. Miscalibrated sensors generate erroneous readings that the controller interprets as correct. Therefore, the system may be operating out of range without any alarm activating.
From Cannabis Vanguard — innovation & science by Excellent Nutrients, we will continue exploring how technology, science and innovation are redefining cannabis production and quality in a rapidly evolving industry.