How to Balance Cannabis Inputs to Improve Results and Efficiency

As cannabis growers endeavor to unlock the full potential of their cultivars, the delicate interplay between lighting and fertigation becomes increasingly paramount, standing as a cornerstone of success in commercial cannabis production.       

In the pursuit of higher potency, increased yields and superior quality, cannabis cultivators are harnessing cutting-edge lighting technologies and innovative fertigation methods. Balancing the costs of those and other inputs with efficiency and understanding where there are diminishing returns is crucial.

By fine-tuning and balancing these fundamental cultivation aspects, growers can maximize efficiency, enhance crop consistency, and fortify their competitive edge in the market.

Lighting & Nutrients: A Not-So-Linear Relationship

Cannabis growers making the switch from high-pressure sodium (HPS) fixtures to high-efficiency light-emitting diodes (LEDs) or who are adopting new nutrient regimens may reasonably believe increasing either feeding or lighting will require a proportional increase in the other input. Similarly, others may believe that by increasing the lighting or nutrient input, yields and quality also will increase proportionally. However, that heuristic only goes so far.

While the reciprocal relationship between light intensity and nutrient delivery generally is linear, there exists a point of diminishing returns with both. “We want growers to be the most nutrient use efficient, so we need to figure out where [lighting and nutrient inputs] begin to plateau,” says Craig Yendrek, a Resource Innovation Institute faculty member and senior scientist with RII member Hawthorne. Delivering high light intensities and nutrient levels may seem like the most straightforward solution, but doing so without paying careful attention to crop response can lead to significant inefficiencies.

“We see growers saying they're successful at really high EC levels with their nutrient solution, and we’re not doubting that they are, but at a certain point you're just flushing nutrients down the drain (if you're using drain-to-waste systems),” Yendrek says.

In its cannabis crop studies, Hawthorne tested the same nutrient ratios at different concentrations measured by electrical conductivity (EC). By applying the same nutrient ratio at ECs of 1.5, 2.0, 2.5, 3.0, and 3.5mS/cm, Yendrek and his team found that “we didn't see any improvement in yield once you got to 2.5 EC and … there could be a lot of nutrient waste because of diminishing returns.”

Light shares a similar response curve to nutrients. While standard HPS fixtures reach a photosynthetic photon flux density (PPFD) of up to 900 on the plant canopy before negatively impacting crop development and environmental balances, most LEDs can reach 1,200 PPFD, with some reaching as high as 1,500 PPFD or more, before seeing diminishing returns or drawbacks. Some genetics may thrive at those higher intensities, but others may have challenges maintaining a healthy growth rate at higher light levels.

“Light energy is the catalyst for photosynthesis, and photosynthesis along with certain hormones will create the efficiency of the development,” says Casey Rivero, a Technical Advisory Council Lighting Working Group member and a cannabis solutions architect at RII member Fluence. “Theoretically, if you give [plants] more light, we say ‘sweet, more photosynthesis.’ But there's a lot of other processes that come into play that help make that photosynthesis effective and efficient.”

Environmental Parameters to Consider

To get the most out of higher light and nutrient doses, cannabis growers need to complete a comprehensive review of environmental controls and settings. Transpiration rates go up as light intensities increase, meaning HVAC systems will need to be adjusted to handle the extra moisture load and stabilized to ensure an effective and efficient plant transpiration rate. “As we're increasing light, we're increasing the plant performance ... because the plant is trying to catch up with what it's doing with the light,” Rivero explains.

Similarly, irrigation events may need to be altered when using higher nutrient concentrations, as well as lighting and CO₂ concentrations (more on CO₂ later). “Lighting, temperature, humidity, carbon dioxide assimilation, those are the four main atmospheric properties that affect plant growth and photosynthesis,” Rivero says. “So having a symbiotic relationship between what's going on in the substrate and what's going on in the environment is super important to pay attention to.”

In addition to improving facility efficiency and efficacy, adopting new technologies and adjusting nutrient recipes to maximize crop yields can also lead to qualitative changes. For example, cannabis flowers can have increased trichome density, or flowers may have more or less purple or pink hues as growers increase lighting intensities and/or nutrient concentrations. That said, it’s important to note that not all genetics will thrive in these souped-up environments.

“I used to have a Panama Red and that thing did great outdoors,” Rivero recalls. “It did great in our low-light level greenhouses. It wasn't a high producer, but the quality was incredible. But when we moved it inside into our more productive rooms, it just drastically failed. It did not thrive with a high light level. It did not like being pushed with nutrients.”

A one-size-fits-all approach is “one of the bigger mistakes that a lot of cultivators are making” when trying to optimize systems for both efficiency and production, Yendrek says. Having the same light levels, nutrient recipes, irrigation and dryback schedules, and other environmental conditions is “going to work for a lot of strains, but it's not going to work for every strain.”

Optimization Notes

Cannabis growers experimenting with lighting intensities and nutrient recipes can use carbon dioxide (CO₂) supplementation to support the photosynthetic process. “As you increase that light, you also need to increase that carbon dioxide to actually process more nutrients, to have a healthier root system that is uptaking the nutrients,” Rivero says. “The more light we give the plant, the more the plant requires out of the environment, out of you as the cultivator, out of the whole process, in order to maximize what you're doing with that light.”

Baseline recommendations for CO₂ concentrations for various crops. Source: Fluence

Resource efficiency is also a consideration with optimization–increasing inputs will necessarily increase costs, and consumers are only willing to pay so much for their products. Growers can look to offset those costs by finding efficiencies in other parts of the operation (e.g. setting controls to stagger when lights turn on to reduce peak loads). Likewise, systems like combined heat and power (CHP) units can be leveraged to produce electricity, heat, and CO₂ simultaneously at a fraction of the operating cost of having three separate systems. CHP units require specialized maintenance and careful facility planning but can help growers maintain optimal environmental conditions while helping them achieve significant savings on energy bills, especially in larger operations.

Cannabis growers also can look at manipulating the crop cycle to balance their increased resource use. Yendrek’s team is experimenting with partner farms to better understand the cannabis crop cycle and ways to reduce inputs without impacting yield or quality. He notes that no definitive answers are ready, but early findings show that there are a few times when growers can dial things back. “If you're currently using a four-week veg duration in your production, I think there are ways to shorten that by trying to go a little bit quicker to higher light levels,” Yendrek says, adding that doing so in conjunction with higher CO₂ levels can reduce vegetation times by one or two weeks.

Other efficiencies can be found in late flowering. “Once you get into late bloom, if you do it right, there's not a whole lot of vegetative growth happening anymore,” Yendrek continues. This means growers can start to dial back light intensities, CO₂ concentrations, and feeding events. “They still need to grow and develop and get those flowers to mature, so I'm not suggesting that you cut the flowering time down, [rather] that the conditions that the plants are growing in probably could be adjusted to save on resources.”

As with any other system adjustments, growers should record a baseline of their current systems before they start experimenting on a small scale. When experimenting, growers should only change one variable at a time and record everything. “Even the things that you might not need right now, it might become relevant later,” Rivero says about data collection. For example, growers experimenting with lighting intensities and nutrient concentrations might also want to record room CO₂ levels to eventually see how changing either of those inputs impacts CO₂ absorption.

Optimizing cannabis production can be an arduous process that occurs over years but developing a deeper understanding of genetics and how they react under different environments can offer growers a competitive edge while establishing the cannabis industry as a resource-efficiency leader in the broader controlled environment agriculture landscape.

Robert Eddy, M.S., is Resource Efficiency Horticulturist at Resource Innovation Institute.