Seed Priming Affects the Germination, Shoot Growth, and Mineral Composition of Four Herbal Microgreens

Seed priming has been widely used as a strategy to improve germination and promote uniform seedling growth in horticultural crops, yet its application in microgreen production remains relatively underexplored. This study evaluated the impact of four priming treatments—hydrogen peroxide, Kelpak Maxx (a seaweed extract), ContinuumTM (a beneficial bacterial biostimulant), and hydropriming—on the germination, shoot growth, visual quality, coloration, and mineral nutrient composition of four herbal microgreen species compared with untreated raw seeds as a control treatment. Four species—chives (Allium schoenoprasum), dill (Anethum graveolens), scallion (Allium fistulosum), and shiso (Perilla frutescens)—were produced as microgreens under greenhouse conditions in two experiments in 2024 and 2025. Results revealed that early germination percentages at 3 days after treatment (DAT) in dill were increased by Kelpak Maxx, Continuum, and hydropriming by 11–18% in 2024 and by 20–40% in 2025, compared with increases for the control of 1% in 2024 and 5% in 2025. Germination percentages at 7 DAT in chives, scallion, and shiso all exceeded 88%, which were similar among priming treatments in 2024 and were not affected by priming in 2025. The four priming treatments resulted in similar fresh and dry shoot weights in chives, scallion, and shiso, but decreased fresh shoot weights in dill by 48.6% in 2024 and by 26.2% in 2025 compared with the control treatment. Species varied in mineral nutrient compositions. Priming altered concentrations of potassium, sulfur, magnesium, boron, and copper in certain species, but otherwise had minimal effects on mineral nutrient concentrations. Seed priming may potentially be used to enhance germination in slow-germinating species; however, it did not consistently improve shoot yield or mineral nutrient concentrations in the four tested microgreen species.