One of the most crucial factors influencing cannabis growth is temperature. Temperature plays a vital role in a plant’s growth processes such as photosynthesis and transpiration, which are responsible for the plant's physical development and nutrient uptake. Temperature is also crucial in the production of a cannabis plant's resins and terpenes. This impacts the quantity, quality, and composition of the final product. Growers in closed growing spaces need to maintain temperatures within optimal ranges for ideal growth.
What is the Ideal Temperature for Cannabis Cultivation?
Generally, optimal temperatures for cannabis growth are approximately 25-30°C (77-86°F) during daytime hours. Ideal night time temperatures are around 17-18°C (63-64.5°F). A temperature difference (DIF) between day and night is important in order to stimulate proper growth.
Temperatures that are too high can elevate susceptibility to many problems, including root rot, spider mites, nutrient burning, and wilting. High temperatures combined with high humidities can result in outbursts of fungal diseases like powdery mildew. Heat damage can also cause damage to leaves and buds, resulting in a yield reduction.
Editor’s Note: Leaf temperatures greatly affect the ability of fungal pathogens to grow. The specific temperatures that are optimal to prevent pathogenesis depend on the pathogen in question. In mammals, it is believed that our body temperature of 98-99 Fahrenheit is ideal for preventing most fungal infections.
If temperatures are too low, plant processes are significantly slowed and will result in an underdeveloped, smaller plant, or even result in plant death. Colder temperatures also make plants more susceptible to certain detrimental plant diseases.
What Affects the Temperature in the Growing Facility?
Several factors impact indoor temperatures and should be taken into consideration by the grower. These include:
- Outside air temperature: The temperature of the air outside of a growing facility impacts the amount of heat being absorbed by the structure and radiated inside. Heat energy will always move from hotter to colder conditions, so the difference between outside and inside temperatures will cause heat to be lost or gained in the growing facility.
- Insulation: Heat exchange through the walls of a structure vary depending on the amount of insulation the walls are equipped with. This directly impacts the amount of energy needed to maintain target temperatures within the growing facility. Different materials have different insulation capacities: polycarbonate can retain more heat than glass, and glass can retain more heat than polyethylene. Insulation can be improved with the addition of thermal screens indoors. It is also improved when a facility is sealed off. Open doors, windows, holes, or leaks will lower the insulation capacity of facilities and should be checked regularly.
- Soil: Heat energy entering the facility also gets absorbed into the soil. Throughout the day, soil heats up, and, at night, the heat is released into the growing facility.
- Machinery: The energy utilized by any machinery within the greenhouse remains inside of the greenhouse. According to the law of conservation of energy, any electricity not used by the machine gets converted into heat energy. In most cases, the most influential addition of energy often comes from HID grow lights. The type of lamp and amount of heat it gives off, its distance from plants, and its dimming settings can all impact temperature in the grow space. LED lights give off significantly less heat and are more energy-efficient than their hotter counterparts such as HPS lamps.
How can temperature be regulated in closed growing systems?
Growers have a number of tools they can use to control temperatures in enclosed growing spaces:
- Ventilation: Ventilation brings air from the outside environment into the grow space and moves the inside air outside. This can be done by opening and closing the growing facility's doors and windows, or with fans pushing air in and out of the structure and circulating air within. Outside air temperatures will impact the temperature change that ventilation will affect; air will move naturally based on the temperature gradient.
- Cooling systems: A variety of options are available for cooling greenhouse spaces. Evaporative cooling systems utilize the physical properties of water changing phases from liquid to gas to cool the environment. Examples include misting and wet pad-and-fan systems. Air conditioning is another option, where air is cooled as it passes over refrigerated coils that have been chilled.
- Heating systems: Heating systems are largely divided into two types: hot water or hot air. In heated water systems, a boiler heats water that runs into pipes or tubes distributed throughout the growing space and heat is given off via conduction or convection. Hot air systems heat the air, typically utilizing a gas burner. The hot air is then distributed to the structure by fan via perforated ducts. Since hot air rises, the location of the pipes or ducts influences the heat distribution and air circulation.
- HVAC systems: These are integrated systems that can be used to both cool and heat enclosed spaces. They involve a series of components which heat, cool, disperse, and ventilate indoor air. They require a substantial amount of infrastructure and electricity, but are more versatile in their abilities.
Many components play a role in temperature regulation around the growing facility. Growers must learn how best to integrate all of these elements in their facility in order to ensure optimal growth and quality. In future topics, we’ll dive deeper into the different types of heating and cooling options that a grower can choose from to create the best conditions.
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About the Authors
DryGair’s writers include a team of experienced engineers, agronomists, and economists. They specialize in climate control in closed growing facilities and practical solutions for effective climate management.