Bridging Yield Gaps in Cannabis Cultivation

In agriculture, a yield gap refers to the difference between a crop’s maximum yield potential and the yield the farmer actually achieves.[1] For cannabis, the yield gap is the difference between the highest possible flower yields and those currently achieved by commercial growers under optimal conditions.

Data from 2018 collected from commercial cannabis growers in Canada found projected yields ranged from as low as 3.36 grams of dry flower per square meter to as high as 3,590 grams.[2] While there is currently no defined yield gap for cannabis, growers probably have room to achieve higher yields, maximizing both production and profit.

A scientific gap

One challenge in closing the yield gap is the lack of scientific knowledge on maximizing cannabis production of cannabinoids.

Until recently, growing cannabis for medicinal and therapeutic purposes was illegal. Commercial production was restricted to hemp (phenotype III), which yields high-quality fiber but low levels of cannabinoids. As a result, most of the existing research on Cannabis sativa focuses on hemp, which has different nutrient needs than drug-type cannabis (phenotype I) grown for medicinal or recreational use. Hemp is also typically grown outdoors, whereas phenotype I is usually cultivated in controlled, indoor environments, requiring different agricultural inputs.

Without much scientific research to reference, growers must work to achieve their crop’s physiological maximum by carefully monitoring and adjusting environmental parameters, nutrient regimes and crop management practices. Each phase of the crop life cycle has particular requirements, and even small deviations can result in yield gaps.

Quantity versus quality

When assessing cannabis yields, growers must consider more than the quantity of buds produced. Chemical composition, particularly cannabinoid content, is crucial for consumers, so growers should seek to maximize crop quality as well. Growers should also factor in secondary metabolites like terpenes and other quality characteristics such as flavor, fragrance and color.

Factors contributing to yield gaps include:

  • Cannabis strain: Each strain has unique genetic characteristics that influence yield potential, growth rates and cannabinoid profiles. Choosing the right strain for the growing conditions that a grower can provide is crucial for avoiding yield gaps.
  • Environment: Temperature, humidity, light and carbon dioxide (CO2) levels impact growth and yield. For example, a meta-analysis found that high-pressure sodium lamps increased cannabis yields over metal halide lamps.[3] Supplementing cannabis with 800–1,000 parts per million of CO2 may increase yields by 40–100%.[4] Simply growing cannabis indoors does not guarantee high yields if environmental conditions are not optimized.
  • Nutrients and supplements: Nutrient needs for maximum yields vary by growth phase. One study found the optimal nitrogen (N) and phosphorus (P) levels during the flowering phase were 194 milligrams per liter (mg/L) and 59 mg/L, respectively, while 160 mg/L of N and 30 mg/L of P were optimal during the vegetative phase.[5] More is not necessarily better. While nutrient deficiencies can cause yield gaps, growers who overfeed P and potassium can cause nutrient toxicities.
  • System hygiene: Biofilms, pathogens and other harmful microorganisms that dwell in hydroponic systems can reduced yield, so it’s important to keep systems clean.

Factors influencing cannabis quality include:

  • Environment: The same factors affecting yields can impact THC and CBD content. For example, light can significantly influence cannabinoid production, with blue-rich light stimulating CBGA accumulation. Light quality can also affect CBDA, THCA and CBCA.
  • Nutrients: Fertilizer impacts quality as well. In one study, plants fed more N (160 mg/L) had lower THCA and CBDA[6] concentrations than plants fed lower N (30 mg/L). However, the low-N plants also yielded significantly less. So, while the plants with the lower N amount had greater potency, it may not be worth the tradeoff of reduced yield.[7]
  • Harvest and processing: Proper harvesting, drying and curing are essential for preserving cannabinoids and terpenes. Any deviation can negatively affect quality.

Meeting regulatory requirements

As important as it is to close the yield gap and grow high-producing, high-quality cannabis, growers must meet the stringent criteria of regulatory bodies and independent organizations to ensure safety.

One such organization is the United States Pharmacopeia (USP), an independent, scientific and public health nonprofit that sets healthcare standards. In 2016, it established an expert panel to develop scientifically based specifications for cannabis, including limits for pesticides residues, chemical toxins, mycotoxins and microbial levels.[8] Not only do contaminants such as these compromise product safety, but they also contribute to yield gaps.

Consistency is a top challenge for medicinal cannabis growers. No two products are the same, and yet selling cannabis for medicinal purposes requires it to be “standardized, consistent and display a quality equal to any New Chemical Entity that has passed muster as a pharmaceutical,” while also minimizing patient risk. Unregulated material that is commonly sold on the street may harbor dangerous chemicals, pathogens and impurities.[9]

By understanding and managing the factors affecting yield and quality—strain selection, environmental controls, nutrient management and contamination prevention—while adhering to the highest safety standards, cannabis growers can thrive in an increasingly competitive industry.

Emerald Harvest Team

[1] Van ttersum, M.K., and K.G. Cassman. 2013. “Yield gap analysis—Rationale, methods and applications—Introduction to the Special Issue.” Field Crops Research 143 (1): 1-3. https://doi.org/10.1016/j.fcr.2012.12.012.

[2] Backer, Rachel, Timothy Schwinghamer, Phillp Rosenbaum, et. al. 2019. “Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield.” Frontiers in Plant Science 10. https://doi.org/10.3389/fpls.2019.00495.

[3] Backer, Rachel, Timothy Schwinghamer, Phillp Rosenbaum, et. al. 2019. “Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield.” Frontiers in Plant Science 10. https://doi.org/10.3389/fpls.2019.00495.

[4] Poudel, Megha, and Bruce Dunn. 2023. “Greenhouse Carbon Dioxide Supplementation.” Published September, 2023. https://extension.okstate.edu/fact-sheets/greenhouse-carbon-dioxide-supplementation.html.

[5] Bevan, Lewys, Max Jones, and Youbing Zheng. 2021. “Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis.” Frontiers in Plant Science 12. https://doi.org/10.3389/fpls.2021.764103.

[6] The acidic forms of THC and CBD.

[7] Bevan, Lewys, Max Jones, and Youbing Zheng. 2021. “Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis.” Frontiers in Plant Science 12. https://doi.org/10.3389/fpls.2021.764103.

[8] USP. 2019. “Re: Scientific Data and Information About Products Containing Cannabis or Cannabis-Derived Compounds; Public Hearing; Request for Comments [Docket No. FDA–2019–N–1482] 84 Fed. Reg. 12969 (April 3, 2019).” Published July 5. https://www.usp.org/sites/default/files/usp/document/public-policy/comment-letter/USP-Comments-to-FDA-on-Products-Containing-Cannabis-or-Cannabis-Derived-Compounds.pdf.

[9] Russo, Ethan B. 2016. “Current Therapeutic Cannabis Controversies and Clinical Trial Design Issues.” Frontiers in Pharmacology 7. https://doi.org/10.3389/fphar.2016.00309.

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