Onions grow from places, which are little onion bulbs, or seeds. Seed-grown onions usually produce large bulbs suitable for storing. In mild Mediterranean climates, you can plant short-day onion varieties in late summer to get a winter harvest or in early spring to get a summer harvest. The seeds grow best when started indoors six weeks before transplanting them in spring or fall. The small seedlings resemble blades of grass at first, but will later produce thick, hollow leaves and massive bulbs as they approach adulthood.
Fill a 2-inch-deep seedling tray using a fine-textured potting soil. Place the tray within a drip pan filled with 1 inch of water. Allow the soil to soak up the water through the slots at the base of this seedling tray till the ground surface becomes moist. Then, empty the extra water in the drip pan.
Sow onion seeds on the ground surface, spacing the seeds one inch apart in rows and also setting the rows at one-inch intervals. Cover the seeds with a 1/4-inch layer of dirt.
Mist the dirt surface lightly with water in a spray bottle. Slide the tray into a plastic bag and then seal it closed. The tote retains the dirt so the dirt doesn’t require water until the seeds germinate.
Put the tray in a warm area indoors where temperatures stay near 70 degrees Fahrenheit. Check the tray daily and then remove the plastic bag once the onion seedling germinate and begin growing.
Go the seedlings to a windowsill in which the young plants can receive at least six hours of direct sunlight. Water the soil once the surface becomes dry.