ASHS 2025 Conference

Spinach is a commonly grown greenhouse crop, thus production practices have been honed over the years. However, additional strategies to improve production efficiency, yield, appearance, and nutritional quality are needed to continue improving the long-term feasibility of production. Light is a major environmental factor that influences the growth and quality of spinach, however, adding supplemental light is energy intensive and can be costly. A strategy to minimize electrical use while increasing crop quality is end-of-production (EOP) lighting where the light provided to the plant is altered just before harvest and not throughout production. The objective of this research was to determine the effect of EOP light intensity, quality, and duration on the growth and post-harvest characteristics of spinach ‘Space’ (Spinacia oleracea). Propagation was 14 days; then seedlings were transplanted into deep-water culture systems and grown for an additional 21 days in a common greenhouse environment. During production, HPS supplemental lighting was used to create a 16-h photoperiod and a daily light integral of 9.0 ± 2.3 mol·m−2·s−1. Seven, 3, and 1 day before harvest, broad-spectrum white LEDs [17:40:43 R:G:B] provided additional light intensities of 0 (control), 100, 200, 400, and 600 µmol·m−2·s−1, and red/blue LEDs [53:1:46 R:G:B] provided 200 µmol·m−2·s−1 for a 16-h photoperiod. At harvest, growth and morphology including fresh and dry mass, plant height and width, and leaf number and nutritional quality including B and C vitamin and carotenoid concentrations were quantified. Post-harvest evaluation was conducted for 3 weeks; fresh mass, color, and nutritional quality were quantified and qualitative appearance data was collected. These results provide insight on how to effectively leverage light intensity, quality, and duration at the EOP to improve the growth and nutritional quality of hydroponic greenhouse-grown spinach.