COMPARING THE EFFECTS OF GREENHOUSE SUPPLEMENTAL LIGHT SPECTRA ON THE DEVELOPMENT AND YIELD OF HIGH-CBD HEMP
Reum, Paul E.
Over the past two decades, indoor production of Cannabis sativa (cannabis) has been rapidly expanding (Summers et al., 2021) (Wartenberg et al., 2021). Indoor production allows growers to control all aspects of the growing environment including cultivar selection, growing media, water use, nutrients, temperature, humidity control, lighting intensity and lighting quality. The optimized production results in a clean, high-quality final product that is suitable for the pharmaceutical industry or high-end market. Currently, indoor cannabis production is a highly energy intensive and ecologically unsustainable practice. Making a transition from sole-source indoor cannabis production (i.e. warehouse) to greenhouse cannabis production with supplemental lighting will result in lower production costs and lower greenhouse gas (GHG) emissions. Currently, there is an overall lack peer-reviewed data to support which supplemental lighting technologies lead to the greatest overall yields in greenhouse grown cannabis. Understanding which spectra of lighting are most beneficial to the development of cannabis in greenhouse production would inform producers on which types of lighting technologies they should invest in. Therefore, to address this gap in understanding, we performed a trial of six supplemental lighting treatments: 60:40 Red:Blue LED, 90:10 Red:Blue LED, Red:Blue LED with a Far-Red peak, high pressure sodium (HPS), Red:Blue LED with a UVA peak, and White LED. Two cultivars (‘TJ’s CBD’ and ‘T2’), were grown during their ten week flowering stage, and effects of light treatments were measured in terms of whole-plant wet and dry-weight, stem and leaf weight, flower weight, and final total cannabidiol (CBD) and tetrahydrocannabinol (THC) concentrations. Overall, the greatest lighting treatment effects were observed within the TJ’s CBD cultivar, with fewer significant differences found within the T2 cultivar. With the exception of growth and height, the White LED treatment outperformed all other treatments. The white LED treatment led to the heaviest plants as well as increased flower yields and higher cannabinoid concentrations.
Master of Professional Studies