ASHS 2025 Conference

Microgreens are increasingly cultivated indoors using artificial lighting, which can be energy-intensive and depending on the species, can have varying effects on yield, commercial quality and nutritional profile. Understanding how light conditions influence plant physiological processes, including growth, phytochemical composition, and nutrient accumulation, is essential for optimizing indoor farming systems. Previous studies indicate that a light intensity of 300 µmol/m²/s enhances growth in microgreens, increasing dry weight and phytochemical content. Extending photoperiods with lower photosynthetic photon flux density (PPFD) has been proposed as a strategy to improve efficiency and plant biomass accumulation under controlled environment. Some photosynthetically active pigments may also be influenced by light manipulation. Carotenoids, a group of pigments that are beneficial to human health, are known to be protective of the photosynthetic system in plants, by regulating the flow of energy and mediating the damage caused by excess light absorption. Continuous lighting can be used to reduce energy costs in microgreen production; however, this may exceed species-specific tolerance thresholds, causing physiological stress. Nevertheless, there is limited information on the effect of continuous lighting on microgreens. To this purpose, a study was conducted in the spring of 2024, at the Penn State greenhouse facilities. We assessed the growth and nutritional responses of pea, radish, and sunflower microgreens under a factorial combination of 16- and 24-hour photoperiods and 150 or 300 µmol/m²/s light intensity. Photoperiod and light intensity impacted all three species of microgreens. Yield was highest under a 24-hour photoperiod at 150 µmol/m²/s. Dry matter content was unaffected by photoperiod but was highest at 300 µmol/m²/s. Regarding phytochemical content, carotenoids increased under continuous lighting and improved at 300 µmol/m²/s. Total antioxidant levels were higher at 300 µmol/m²/s compared to 150 µmol/m²/s. On the other hand, nitrate content increased under shorter photoperiods and lower light intensity, a trend also observed for total nitrogen, and iron concentration at 16-hour photoperiod and 150 µmol/m²/s. These findings indicate that all three microgreen species tested tolerate continuous lighting with positive or no effects on yield and nutritional quality, suggesting that light intensity and continuous lighting can be used in controlled environment systems to enhance the commercial quality and nutritional profile of microgreens.