Cannabis plants are fundamentally dependent on their environment, and temperature controls their growth and health. A certain degree of warmth is a biological necessity for every stage of a cannabis plant’s life. Successful cultivation hinges on maintaining temperatures within a specific range that changes as the plant matures. Understanding this relationship is the foundation for maximizing the quality and quantity of the final harvest.
Temperature’s Role in Plant Metabolism
Temperature acts as a direct regulator for the internal biological machinery of the cannabis plant. All the plant’s chemical reactions are controlled by enzymes, which have an optimal temperature where they function most efficiently. When the temperature is too low, enzyme activity slows significantly, reducing the speed of growth and development.
Photosynthesis, which converts light energy into chemical energy, and respiration are both highly dependent on temperature. Respiration, the process of breaking down sugars for energy, can become disproportionately high in very warm conditions, causing the plant to burn more energy than it creates. The speed at which a plant absorbs water and nutrients from the root zone is also tied to the temperature of the medium and the surrounding air. If the root zone is too cold, uptake slows drastically, leading to nutrient deficiencies.
Ideal Temperature Conditions for Growth Stages
The temperature requirements of a cannabis plant shift based on its current phase of development. During the vegetative stage, when the plant is focused on producing stems and leaves, a warmer environment encourages rapid growth. Ideal daytime temperatures during this phase typically fall within the range of 70–85°F (21–29°C).
This warmer environment supports the high metabolic activity required for the plant to build a robust structure. Managing the air’s moisture content alongside temperature is also important, a concept known as Vapor Pressure Deficit (VPD), which regulates how efficiently the plant transpires and absorbs nutrients.
Once the plant transitions into the flowering stage, the ideal temperature range shifts to a slightly cooler window, generally between 65–80°F (18–27°C) during the daytime. Maintaining a cooler temperature during this phase is linked to the preservation of terpenes and cannabinoids, which can degrade under excessive heat. Cultivators often aim for a slight temperature drop, perhaps 10°F or 6°C, during the dark period to mimic natural outdoor conditions. This temperature differential between day and night can help promote healthy growth and may encourage the development of vibrant colors in certain strains.
Managing Temperature Stress
Deviating from these optimal ranges introduces significant stress that impacts plant health and yield. Heat stress occurs when temperatures exceed the plant’s tolerance, leading to symptoms like upward leaf curling, sometimes described as “tacoing,” as the plant tries to protect itself. Prolonged high temperatures during flowering can cause bleaching on the tops of buds and “foxtailing,” where new, airy growth emerges from mature buds.
Mitigation for heat stress involves improving air circulation and ventilation to remove trapped hot air, or using air conditioning. Growers may also need to increase the distance between the plant canopy and the light source, as high-intensity lights are a common source of localized heat.
Conversely, cold stress slows down all metabolic processes, resulting in stunted growth and reduced nutrient uptake. A common symptom is the appearance of purple stems and petioles, and the plants become more susceptible to mold and mildew due to the combination of cold and high humidity.
Remedies for cold environments include using space heaters or heating mats for seedlings to keep the root zone warm. Insulating the grow space and ensuring plants are not sitting directly on cold floors can also prevent the root temperature from dropping too low. Maintaining a steady climate is a continuous challenge, requiring regular monitoring and adjustments to ensure the plants remain within their preferred temperature zones.