December 10, 2024
Increasing light intensity in a cultivation system for crops like cannabis and lettuce is much like installing a powerful sports-car engine into a vehicle. Just as a high-performance engine requires upgraded tires and a reinforced body to handle enhanced speed and stress, plants grown under higher intensities require all other environmental conditions to be finely tuned. If these environmental factors—such as nutrients, water, CO₂ levels, and temperature—are not optimized, increasing intensity will not yield the desired result and may lead to ‘light stress’.
Growing under high light intensity, for cannabis and for other leafy plants, is akin to driving in the fast lane: everything happens more quickly, and any mistakes or imbalances become more pronounced and harder to correct. This accelerated growth environment means that issues can develop rapidly, leaving less room for error and adjustment.
This document is designed to prepare growers for the challenges and opportunities of high-intensity light cannabis and other plant cultivation. It provides comprehensive guidance on what factors should be considered and how to adjust all environmental parameters to work in harmony with increased light levels.
By following these recommendations, growers can ensure their plants effectively utilize the additional light, leading to healthier crops and higher yields.
The Plant Environment: Factors to Consider
Irrigation/Nutrition
Water use will increase when you increase the intensity of light. Since the plants are “drinking more,” irrigation needs also increase. In theory, water use efficiency (defined as the ratio of biomass to water use) remains relatively constant. So, when cannabis plants are “drinking more,” they are also growing more in equal proportions. This means that in theory no changes need to be made to fertilizer solution composition/concentration as long as irrigation increases in proportion to biomass produced/water used.
That said, excessive fertilization or imbalanced solutions may cause more problems at high light (in the fast lane) that may not appear at lower intensity. Overall, we recommend a review of plant irrigation and nutrition when considering high intensity light.
Temperature
The most important factor to consider is the effect of higher intensity of light on canopy and more importantly, flower temperature. More light means more energy and heat will reach the plant. So, air temperature may need to be lowered to balance canopy/flower temperature. For an in-depth academic review of the effect of light intensity on temperature, see Analysis of Environmental Effects on Leaf Temperature under Sunlight, High Pressure Sodium and Light Emitting Diodes by Jacob A. Nelson and Bruce Bugbee.
CO2
We have often heard it said that “CO2 enrichment is only valuable at high light, and more CO2 enrichment is more valuable at higher light.” We respectfully disagree – CO2 is always valuable. Our recommendation is always enriching to 1200 ppm – regardless of intensity. Research conducted in Dr. Bruce Bugbee’s lab at Utah State, CO2 enrichment increased yield the same amount at a DLI of 32 and 64 mol/m2/d. There is no need to adjust CO2 concentration when increasing the intensity of light, and there is no need to elevate above 1200 ppm.
If you are not enriching with CO2, and only relying on air exchanges, then CO2 enrichment does become more valuable with high intensity light. If air exchange is inadequate, CO2 can be drawn down to below ambient because of increased photosynthesis. CO2 depletion below ambient reduces yield more than CO2 enrichment increases yield.
Humidity/VPD
Higher light means more water moving through the plants, and this will increase the humidity if dehumidification is inadequate. From a plant perspective, there is no reason to change humidity/vpd setpoints with high intensity light. One exception could be to increase VPD to 1) increase nutrients moving through the plants and 2) increase evaporative cooling/lower canopy temperature.
Airflow
High intensity light can mean more compact plants and dense canopies, making sufficient airflow even more important. Sufficient airflow helps manage canopy/flower temperature and minimize microclimates where humidity can increase and CO2 can deplete. Additional airflow may be needed when increasing light intensity.
Infrastructure/Environmental Control
Power/Energy Capacity
Increasing intensity in your cannabis cultivation system’s lighting inevitably leads to higher energy consumption. This surge can place a significant strain on your facility’s electrical infrastructure. It’s essential to evaluate whether your current power supply and distribution systems can handle the additional load safely and efficiently. Upgrading electrical panels, wiring, and circuit breakers might be necessary to meet the new demands.
Higher energy usage also translates to increased operational costs in cannabis and other agricultural cultivation systems. To mitigate these expenses, consider investing in energy-efficient lighting solutions like high-efficiency LED fixtures. LEDs offer high light output with lower energy consumption compared to traditional lighting systems like high-pressure sodium (HPS) lamps. They also produce less heat, reducing the burden on your HVAC systems.
Implementing energy management strategies can further optimize power usage. Utilizing programmable lighting controls, dimming capabilities, and scheduling can help reduce energy consumption during peak demand times, potentially lowering utility costs. Exploring renewable energy options, such as solar panels or wind turbines, can also offset energy costs and contribute to a more sustainable operation.
Be aware of potential incentives or rebates offered by utility companies or government programs for adopting energy-efficient technologies. These incentives can help offset initial investment costs and improve the return on investment for upgrading your lighting systems.
HVAC/Dehumidification Capacity
With increased intensity of light comes additional heat, even with energy-efficient lighting systems. This added heat can increase temperatures above optimal ranges for cannabis and leafy plant growth, and may require upgrades to your HVAC systems. Adequate cooling capacity is essential to maintain the desired air temperature and prevent heat stress on the plants.
Dehumidification capacity is another key factor to consider when increasing light intensity. Transpiration rate increases with increasing the intensity of light, leading to an increased demand for dehumidification to maintain optimal humidity levels within the growing environment. Elevated humidity can create conditions favorable for fungal diseases, reduce evaporative cooling of leaves leading to higher canopy/flower temperature, and reduce nutrient uptake. For these reasons, it’s imperative to assess and potentially upgrade dehumidification systems to handle the increased moisture load.
Integrating advanced environmental control systems can provide precise regulation of both temperature and humidity. These systems can monitor real-time conditions and adjust HVAC and dehumidification equipment accordingly to maintain ideal growing conditions. Energy recovery ventilators (ERVs) can also be utilized to exchange indoor air with outside air efficiently, recovering energy from the exhausted air to pre-condition incoming air, thus saving energy. However, this technology makes it difficult to enrich CO2 above ambient, so tradeoffs between energy consumption and potential yield increases must be considered.
Cultural Practices
Planting Density
Under high intensity light, plants have access to more photons for photosynthesis, potentially supporting denser planting without sacrificing individual plant performance. However, increased planting density can exacerbate competition for other essential resources such as CO₂, and can lead to reduced airflow and increased humidity within the canopy.
Adjusting planting density requires a careful balance. Higher densities may maximize space utilization and yield per unit area, but can also increase the risk of disease and create microclimates unfavorable for plant growth. Conversely, lower densities may improve airflow and light penetration but may not fully capitalize on the enhanced light environment.
Conducting small-scale trials to determine the optimal planting density under increased light conditions can provide valuable insights. Factors such as plant architecture, growth habit, and cultivar should be considered when adjusting planting densities. Collaboration with the team at Due Diligence Horticulture can aid in developing density strategies that align with your production goals.
Pruning/Defoliation
Effective canopy management becomes even more critical under high intensities. The accelerated growth can lead to denser canopies, which, if left unmanaged, reduce light penetration to lower leaves and flowers, and impede airflow. Pruning and defoliation practices should be adjusted to maintain an open canopy structure that maximizes light interception and minimizes disease risk.
Regular pruning helps remove excess vegetative growth and promotes uniform development. Defoliation, particularly of older or shaded leaves, can improve airflower, minimize microclimates, and enhance photosynthetic efficiency throughout the plant.
With the incorporation of under canopy lighting, canopy management strategies may change, and less labor may be needed to remove leaves and flowers lower in the canopy by uniformly delivering light throughout the canopy. Under canopy lighting therefore offers an opportunity to increase overall light intensity, while reducing the need for pruning and defoliating to ensure consistency and quality of flower buds throughout the canopy. Adjusting pruning schedules to match the accelerated growth under high light conditions ensures the greatest return on your investment into more light!
