Four herbal microgreen species varied in optimal seeding densities and growing substrate for maximized shoot yield and mineral nutrients

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The microgreen industry in North America has experienced continuous growth, with an increasing number of species, including vegetables, herbs, and grains, being produced as microgreens. Cultural practices significantly impact the productivity and nutrient composition of various microgreen species. The hypothesis of this study was that optimal cultural practices, including seeding density and substrate type in microgreen production, should be species dependent. This study investigated shoot growth, visual quality, and mineral nutrient compositions of four herbal microgreen species, including basil, chives, scallion, and shiso, in two experiments as affected by five seeding densities, including 75, 150, 225, 300, and 375 g·m−2, when grown with a peat-based soilless substrate, and a hydroponic mat made from jute fibers. Microgreen fresh shoot weights generally increased with increasing seeding density, with scallion producing the highest fresh shoot weight at 375 g·m−2, whereas the 375 g·m−2 seeding density increased fresh shoot weight compared with 75 to 225 g·m−2, but resulted in similar fresh shoot yield to 300 g·m−2 in basil, chives, and shiso. Scallion and shiso microgreens produced higher fresh shoot weight when grown on peat-based substrate, while basil and chives produced higher fresh shoot weight on jute mat compared with peat in one or both experiments. Substrate type also altered mineral nutrient concentrations in tested microgreens with peat substrate increasing phosphorus (P), potassium (K), calcium (Ca), and sulfur (S), and jute mat increasing nitrogen (N) and magnesium (Mg) in one or more species.