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Optimal growing conditions for medicinal cannabis under efficient LED spectrum

Hortilux's mission is to increase useful knowledge for growers so that they get the most return from their grow light installation. As part of that mission, the company has conducted research into the ideal light and temperature conditions for medicinal cannabis in collaboration with Wageningen University. The results of this study provide growers with valuable insights to optimize their production and improve the quality of their end product.

From the left: Leo Marcelis, Mexx Holweg and Stephane Andre'

Energy efficiency
The efficiency (in µmol/joule) of the LED spectrum has a major influence on operational costs. The more blue and green in the spectrum, the more electricity consumption for the same amount of grow light. By choosing a spectrum with at least 80% red, a grower can save an average of 30% energy compared to a daylight spectrum. But how do the plants perform under such a spectrum and what is the effect of the temperature? These questions formed the starting point. The setup included 3 light intensities during the flowering phase: 600, 900 and 1200 µmol/m2/s with an efficient spectrum (80% red without far-red). Two were used cultivars one high in CBD and one high in THC. For the temperatures, 2 crops had a low (25/21°C) and 2 crops a high (31/27°C) air temp during the flowering phase. In total, 3 were the key measurements taken into account: yield, Light Utilization Efficiency (grams of flower/mole of light) and cannabinoid concentration.

Improved yield and quality
The research has shown that higher light intensity leads to a significantly higher flower yield and better quality. The Light Utilization Efficiency (LBE) is the only pure unit to determine how grow light performs under different intensities. The research shows that there is no flattening at 1200 µmol/m2/s. Every mole of grow light is converted into dry flower production just as well as at lower levels. In addition, the harvest index increased at this high light level: the ratio of flowers to non-harvestable material. Simply put, the flowers are heavier and have fewer unusable leaves to remove, resulting in faster post-harvest processing.

Leo Marcelis, researcher at WUR, says: "Medicinal cannabis is a very special and interesting crop. The plants have a very high light requirement and the leaves show a particularly high photosynthetic rate. The yield of flowers increases linearly with light intensity, even up to 1200 micromol/m2/s."

Lower temperature
What emerged most clearly is the beneficial influence of the lower temperature on the overall production and concentration of cannabinoids, the active ingredients in cannabis. Regardless of light intensity or cultivar, there was significantly higher production and concentration in colder treatments. These differences were consistently visible in the flower samples analyzed as early as 20 days before harvest.

Optimal growing conditions
The difference between the 2 cultivars within this study shows that each variety has its own optimal light/temperature combination. This research questions the RTR (Ratio Temperature Radiation) approach to cannabis production, because with 2 very different genetics we can conclude that the highest production and concentration of cannabinoids can be obtained under a combination of low temperatures (25/21°C ) and high light intensity (1200 µmol/m2/s).

Stéphane André, grow light consultant at Hortilux: "A higher light intensity with our spectrum results in directly proportional increased production and improved quality. This has been confirmed by the WUR. Because our LED fixtures were in a separate and cooled room, we were able to accurately investigate the effect of temperature. We did not expect that the production and concentration of ingredients would be higher at a lower temperature. It offers opportunities to further optimize cultivation and achieve higher yields. "

Important advantages for growers
The results of this study supposedly offer a few benefits to medical cannabis growers, such as higher yield: A higher light intensity leads to a higher yield per square meter. Higher concentration: A lower temperature results in a higher concentration of cannabinoids. Higher quality: more dry weight to the flowers and faster post-harvest processing. Energy savings: by choosing an efficient spectrum, energy consumption can be significantly reduced.

Mexx Holweg, researcher at WUR, concludes: "This research has made me realize how crucial it is to improve and standardize the production of medicinal cannabis. Finding the right balance between maximum yield of specialized metabolites and minimum energy input, while also achieving uniformity within the crop, is a challenging but essential goal. It ensures that the concentration of ingredients always falls within the regulations.

For more information:
Hortilux
www.hortilux.com

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