How does a cannabis cultivation business survive in 2024? The answer is simple: cash flow. For most cultivators, cash flow is generated by selling flower, which depends on their ability to leverage plant science to produce it. As long as a grower’s cash flow from sales exceeds their expenses, they can keep the doors open. In other words, their sales price per pound must be higher than their cost per pound.
Many cultivation businesses have a 1:1 relationship between labor costs and plant count, but this isn’t always true when it comes to costs and yields. In our previous column, we discussed the importance of a perpetual weekly harvest schedule, maintaining cycles of the same size and plant count. One key benefit of this approach is that it stabilizes costs, allowing for more predictability and control over expenses and fixed costs throughout the year—per day, per week and per month.
Once a cultivator establishes this consistency, they can shift focus to internal cost improvements by further leveraging crop science to increase yield while reducing the cost per pound. Let’s say that again: If you have a fixed cost structure and are able to produce higher and higher yields, this will drive your cost per pound down. You can only do so much with headcount reductions, system efficiency and materials pricing. There is a point where a cultivation business must improve their crop performance to be as competitive as they can be.
Most people recognize that light is a key factor in plant growth, but how well do we really understand its impact? Let’s dig in and demystify yield.
The Energy Cascade Model: A Framework to Understand YieldThe energy cascade model (ECM) provides a framework for understanding how light energy is converted into the flowers you harvest. The process involves capturing light (photons), using it to drive photosynthesis, and distributing biomass efficiently into flowers. Understanding this model allows growers to optimize yield by identifying opportunities to improve efficiency at every step. Maximizing efficiency is the foundation of your entire production system, whether you’re growing indoors, outdoors, or in a greenhouse.
The ECM can be broken down into three key steps:
Photon Capture: Harvesting LightPhotosynthetic Efficiency: From Light to BiomassBiomass Partitioning: Directing Biomass to Flowers
By following these steps—from photons to flowers—we arrive at Photon Conversion Efficiency (PCE). This unifying metric allows growers to quantify production efficiency and offers investors insight into the long-term sustainability and competitive advantage of a cannabis cultivation business. Let’s delve into each component to identify ways to enhance efficiency.
Photon Capture: Harvesting LightPhoton capture is the first and most crucial step in optimizing yield. Just as you aim to optimize every inch of space in your grow room, you must also optimize the use of every photon delivered to your plants. Your goal is to ensure that the largest possible proportion of the light is captured and used for growth.
Photon capture is dynamic throughout the lifecycle, starting low early in the lifecycle and approaching a maximum near 100% later in the lifecycle. Averaged over the lifecycle, a typical crop of cannabis absorbs about 60% to 70% of the photons applied.
Plant density, canopy management, and light distribution are all crucial factors in determining photon capture. Research out of the Institute of Soil Water and Environmental Sciences, Volcani Center, has shown that by increasing plant density, you can significantly increase photon capture and yield by up to 44%, though this must be balanced with the need to maintain chemical uniformity across the crop and your desired finished flower ratios (ratio of As to Bs and Cs).
This same research, along with research out of Clemson University, has shown that by managing the canopy through strategic pruning instead, as shown in Figure 1, growers can improve canopy structure, ensuring light penetrates to lower leaves and flowers, boosting photon capture and balancing chemical uniformity.
However, as growers pursue higher yields, with plant density being one consideration, balance, is key. The quality of this yield—not only in chemical uniformity but also biomass category ratio—demands close attention. When plants are very compact and dense, does increased plant density reduce premium A and B flowers? Can strategic canopy management deliver preferable results?
Operational expenses must be considered as well. In most systems, not only does 1% more light equal 1% more yield, but 1% more plants equal 1% more labor cost. Most cannabis cultivation systems have very little automation aside from a pot filling line (if that) and a conveyor. But by managing your crop and maximizing captured photons you can optimize your yield and the quality of that yield, without just taking on more plants and risking costs and quality.
In short, the more photons you capture, the more energy your crop will have for photosynthesis—the next step in the energy cascade.
Photosynthetic Efficiency: From Light to BiomassOnce photons are captured, the next step is converting the energy in light into biomass through photosynthesis. This process, however, is not perfectly efficient. Photosynthetic efficiency refers to how effectively plants use absorbed light to fix CO2 into carbohydrates, which ultimately fuel growth and biomass production.
The theoretical maximum photosynthetic efficiency is around 11%, but practical efficiency is much lower. Empirical studies, including work by Dr. Keith J. McCree that led to the famous McCree curve and the definition of photosynthetically active radiation (PAR), showed that under ideal conditions, the maximum photosynthetic efficiency of a single leaf is about 8%.
Photosynthesis already stands out as a particularly inefficient process (10x lower than photon capture), but things get worse when we scale from McCree’s studies to production facilities. A typical photosynthetic efficiency seen in cultivation environments is about 3% to 5%. Though this may seem like a small difference, it can result in nearly a two-fold change in biomass production.
To maximize photosynthetic efficiency, growers must carefully manage the growing environment to minimize plant stress. Key factors include temperature, CO2 levels, and nutrient availability. CO2 enrichment, for example, can boost photosynthetic efficiency by up to 40% when raised from ambient levels to 1200 ppm.
By maximizing photon capture and photosynthetic efficiency, growers can increase the biomass available for partitioning into flowers—the final step.
Biomass Partitioning: Directing Biomass to FlowersThe final step in the energy cascade is biomass partitioning, which refers to how biomass generated through photosynthesis is distributed among leaves, stems, roots, and, most importantly, flowers. Your goal as a grower is to maximize the amount of biomass that goes into flowers.
Biomass partitioning—like photon capture—is dynamic over time, starting low early in flower and approaching a maximum near the end. Harvest index, the ratio of flower yield to total biomass at harvest, is a critical measure of biomass partitioning efficiency. In most cases, harvest index is around 0.5 to 0.6 (50% to 60%).
Growers from greenhouse to indoor—those who have control over their lighting—range from ratios of 50:50 up to 20:80 trim to flower. From there, growers are all over the board in how they categorize and sort flower categories. Some only having A and B flowers, while others have A through E flowers, with each category having a different sales price and a different cost per pound. Growers should work to have more uniform consistency within biomass categories and fewer categories in general, alongside a higher harvest index.
Techniques such as low-stress training, topping, and strategic pruning have the potential to increase harvest index by directing more energy to flower development. Environmental factors may also influence biomass partitioning. For example, various studies have shown that high light intensities and elevated CO2 can improve biomass allocation to flowers.
Mastering Efficiency for Long-Term SuccessIn today’s competitive market, growers must be laser-focused on increasing efficiency. Just as with square foot utilization, maximizing your photon conversion efficiency directly impacts your cost per pound. If you can lower your cost per pound while maintaining quality, you can afford to ride out market fluctuations better than competitors who are stuck with higher operational costs. In an industry where prices can swing dramatically, the most efficient grower is often the most resilient.
The cannabis market is only going to get tougher, with more competitors entering the space and margins tightening. Those who understand and optimize their crop’s photon conversion efficiency will be the ones who thrive. It’s all about using every photon, every inch of space, and every resource as efficiently as possible. If you want to stay ahead, now is the time to fine-tune your efficiency, reduce your cost per pound, and position your operation for long-term success.
Travis Higginbotham is founder and CEO of Due Diligence Horticulture, a professional horticultural operations service provider that supports growers in all horticultural markets, globally. A recognized authority in both traditional commercial horticulture and cannabis production, Higginbotham holds a B.S. in Horticulture from Clemson University and an M.S. in Horticulture from Virginia Tech. He is co-inventor of two smart farming patents, and with former experience leading global technical support teams, research and production at scale in the U.S. F. Mitchell Westmoreland, Ph.D., serves as Director of Science at Due Diligence Horticulture. He has a deep-rooted background in plant science, earning his Ph.D. from Utah State University with a specialization in plant-environment interactions in controlled environments. His research, widely published in peer-reviewed journals, focused on photobiology and plant nutrition, particularly in cannabis cultivation. Westmoreland has been recognized with multiple awards, including Doctoral Student Researcher of the Year and Graduate Student Teacher of the Year.
Digging in to the dynamics of photon capture, photosynthesis, and biomass partitioning to demystify yield. Read More
