This study was conducted on Melissa officinalis (lemon balm) to compare the effects of seed vigor tests, under laboratory conditions, on seedling emergence from soil (greenhouse) and to study the effects of foliar application of iron oxide nanoparticles (ION) on growth variables and physiological performance of Melissa officinalis seedlings. Seed vigor tests were conducted on seeds of three sizes (large, medium, and small) in the laboratory. These tests included standard germination, accelerated aging, cold, Hiltner, and electrical conductivity (EC). Seeds of three sizes were planted in two different soil types, namely loam and clay loam, in a greenhouse. At the two-node stage, foliar applications of iron oxide nanoparticles (control, 15, and 30 ppm) were also made. The Hiltner test best predicted seedling emergence form the soil, whereas the other tests showed no significant predictive power. The findings indicated that the combined treatment of large seeds plus clay loam soil plus application of 30 ppm ION produced the highest seedling height, chlorophyll a and chlorophyll b levels, soluble sugars content, essential oil percentage, and gas exchange, while the combined treatment of small seed + loam soil + no foliar ION application resulted in the lowest levels of these variables. Loam soil with small seeds and no foliar ION spray increased proline concentration and antioxidant enzyme activity. Results of soil texture analysis and Hiltner seed vigor test were found crucial for farmers who cultivate Melissa officinalis L. Finally, ION foliar spraying is suggested for better physiological performance and yield of this plant. تفاصيل المقالة