Microgreens are vegetable and herb seedlings harvested shortly after the emergence of the first true leaf and prior to leaf expansion/senescence of cotyledons. Microgreens represent a quick turn, potentially high value crop that consumers value for their nutrition, flavor, and aesthetic appeal.
Because many microgreens species start with a large seed that can feed early seedling growth until harvesting it is thought by many that microgreens don't require additional fertilizer inputs. The objective of our first experiment was to determine the impact of liquid fertilizer concentration on harvestable yield of three microgreen species: arugula (Eruca sativa L.), mizuna (Brassica rapa L. var. japonica) and mustard (Brassica juncea 'Garnet Giant'). These three species were used to represent a diversity in appearance and taste but share similarity in seed size, days to harvest, and cultural requirements. The objective of this study was to determine how three species of microgreens would respond to concentration of water soluble fertilizer and substrate depth. Seeds were purchased from Johnny's Select Seeds (Winslow, Maine).
Seed was broadcasted over a peat/perlite potting mix (Lambert LM-111) in 10" x 20" trays containing 2401 cell inserts (i.e. 24 cells per tray) at a rate of 125 seeds per cell (equivalent to 3,000 seeds per 20"x10" flat). Trays were overhead watered and covered with a propagation dome followed by a tray placed over the top of the propagation dome to exclude light. Seeds were germinated at 68 °F for 48 hours before the dark dome was removed. The germination dome was removed 48 hours thereafter. Trays were placed into fertilizer treatments receiving either clear water (0 ppm fertilizer) or Jack's 21-5-20 water soluble fertilizer at 50, 100, 150, and 200 ppm nitrogen. After seeding, plants were watered about every three days with their corresponding fertilizer treatment, which was applied via subirrigation by placing the tray in a container holding about 3 cm of nutrient solution for about three minutes. Microgreens were hand harvested when the average first true leaf measured a 1/2 inch in length.
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