Agronomic approaches for increasing food crop yield and quality are crucial for boosting food security due to the depletion of terrestrial resources and the rising worldwide demand for food. As a consequence, the current study looks at ways to improve several essential components of existing onion production technique in Egypt by using two types of potassium fertilizer, KCl and K2SO4, either alone or in combination, as well as two different planting methods, seeding and seedling transplantation. The research focused on the performance of onion cv. Giza 9 through vegetative growth, bulbification (bulbing ratio), dry bulb yield and bulb quality during the successive winter seasons of 2019/2020 and 2020/2021. The obtained results demonstrated that direct seeding of onion produced higher plant growth, bulb yield, and quality than seedling transplantation. Compared to potassium combinations involving chloride, potassium fertilization of onion in the form of K2SO4 produced the best plant growth, bulb production, and their quality. As chloride levels in fertilizer compounds rise, onion plant growth and yield potential decline. On the other hand, chloride had a less negative impact when onion was grown from seeds rather than seedlings. Also, direct seed sowing and fertilization interactions with either pure K2SO4 or a mixture of 75% K2SO4 and 25% KCl resulted in the highest dry bulb yield measurements. Interestingly, supplying the onion plants with KCl fertilizer up to 25% of their potassium requirements without causing a significant decline in plant growth or bulb yield when planting onions by direct seeds but not to seedlings.