Seeding Density Outweighs Light Intensity in Microgreens Yield on a Vertical Farming System

The optimal photosynthetic photon flux density (PPFD) and seeding density (SD) combinations for microgreens production on vertical farming systems remain unclear for many species. This study aimed to determine the effects of PPFD (50, 100, 150, and 200 µmol m−2 s−1) and SD for sunflower (1275, 1700, and 2125 g m−2), radish (272, 340, and 408 g m−2), and green and red cabbage (126, 180, and 235 g m−2) microgreens. PPFD had no effect on the yield of sunflower, radish, or red cabbage, indicating that 50 µmol m−2 s−1 was sufficient to meet plant demands. Green cabbage yield increased ~10% at 150 µmol m−2 s−1. Increasing SD enhanced yields, with gains of up to ~22%, 49%, 52%, and 30% for sunflower, radish, green, and red cabbage, respectively (1700, 408, 235, and 180 g m−2). PPFD did not affect the nutrient content of sunflower, likely due to its high seed reserves. A higher SD increased anthocyanin in red cabbage but diminished its content in all other species. Our findings highlight that SD is more impactful than PPFD on determining yield, at least under low irradiance, in sunflower, radish, and red cabbage microgreens grown on indoor vertical farming systems.