Far Out! – the effects of far-red light on Cannabis

Abstract Far-red (FR) light elicits two distinct processes in plants. First, a shade avoidance response which is triggered when the ratio of red to FR (R:RF) declines. Second, the Emerson effect in which the efficiency of photosynthesis is improved by the combination of FR and R light. We investigated whether we could harness these phenomena in medicinal Cannabis to improve yields so that the duration of the photoperiod could be reduced to 10 hours (“10L”) whilst returning similar or improved yields compared to a 12 hour photoperiod (“12L”). The THC concentrations were elevated in both high THC varieties by the different FR treatments. In Hindu Kush the concentration of THC was elevated by the addition of 4 hours of total FR (“10L_2_2D”), and in Northern Lights total cannabinoid yields were increased by nearly 70% over the 12L control by the addition of 2 hours of FR in darkness after 10 hours of light (“10L_2D”). Our results show a strong yield and quality advantage in high THC lines treated with end-of-day FR treatments. Furthermore, a lighting schedule of 10L_2D instead of 12L would result in a saving of 5.5% in power usage and resultant emissions.