Cannabis was domesticated in Central Asia over 6,000 BCE and has become an important plant for medical, recreational, and industrial applications . Cannabis growers are challenged to create conditions that maximize yields. In the study “Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield,” past studies on commercial cannabis production are reviewed. The yield gap is the difference between the maximum possible cannabis flower yield compared to current yields obtained in commercial production, while also considering cannabinoid concentration and cannabinoid proportions.
Cannabis flower yields are highly variable and can be influenced by a large variety of factors. Those factors include genetic variety, plant density, light intensity, and fertilization . THC potency and yield can also be influenced by pot size, light type and duration of the flowering period. This study asks three main questions:
- What is the maximum yield a plant variety is capable of achieving?
- What conditions can achieve the maximum yield?
- What are the main factors contributing to cannabis yield per plant, per square meter, and per watt (W) of lighting electricity?
Cannabis Plant Yield Versus Plant Density and Pot Size
The maximum yield that a cannabis variety is capable of achieving is different for each variety so each will have a different target. Increasing plant density (plants per square meter and per watt of light) is one strategy that growers use to try to maximize yields. However, there is a point where increasing cannabis plant density reduces yields because there are not enough resources like light and carbon dioxide to support growth . When it comes to pot size, increasing pot size can reduce THC content in some cannabis varieties like White Widow
Cannabis Fertilizer for Maximizing Yields
Fertilizing with abscisic acid, a plant stress hormone, can increase THC production . Using slow release versus immediately available fertilizer and different fertilizer nutrient compositions and proportions also play a major role in yield. Fertilization can influence cannabinoid content. Researchers found that while it does not impact yield per square meter, fertilization practices do impact yield per watt of light. Utilizing additional plant growth promoting rhizobacteria helps plants utilize nutrients better, helps combat pathogens, makes plants more resilient to stress, and improves cannabinoid production.
Influence of Lighting on Cannabis Yield
The research team observed that yield per square meter is higher with high-pressure sodium (HPS) lamps than metal halide (MH), but may not consider new ceramic metal halide technology . Traditionally, HPS lamps have higher light efficiency and higher photosynthetic photon flux density (PPFD) than MH lamps. 600 watts per square meter has been reported as ideal for increasing cannabinoid production. However, 600 W lamps have historically had performance issues so growers in practice often avoid them. Cannabis plants are also sensitive to the color of light in addition to the intensity, with far-red light being key to growth stage responses. New LED grow lights with improved color spectrum are becoming a popular way to increase energy efficiency while maintaining light quality.
Increasing duration of the flowering period has been observed to increase yields and THC content . For cannabis, the maximum rate of photosynthesis occurs at 30°C, 750 μmol CO2 mol−1, and under 1,500 μmol m−2 s−1. Studies have demonstrated that higher light intensity in drier and more carbon dioxide (CO2) rich environments boosts photosynthetic activity and water use efficiency.
Recommendations for Closing the Cannabis Yield Gap
Cannabis yield per square meter and per watt of light can be increased in five ways :
- Use a planting density of no more than 12 plants per square meter
- Flower plants for 9 weeks
- Utilize HPS lamps or LEDs
- Implement an adequate fertilizer regime
- Design your lighting to maintain energy efficiency instead of cannabinoid accumulation
Cannabis growers should also consider the unique preferences of different varieties . Understanding genomic differences will help guide growers in adjusting cultivation conditions to meet a variety’s specific preferences and achieve their specific potentials.
- Backer R, Schwinghamer T, Rosenbaum P, et al. Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield. Frontiers in Plant Science. 2019;10. doi:10.3389/fpls.2019.00495 Accessed 30 May 2021 from https://www.frontiersin.org/articles/10.3389/fpls.2019.00495/full
Image: https://pixabay.com/photos/woman-smile-marijuana-hemp-5870185/ by DimStock on Pixabay