Growing an onion in your garden is an easy project: It will grow fast, and it won't take up a lot of room. When you shop for your onion seed you will notice that there are two types, long-day and short-day. The long-day varieties, such as Sweet Spanish and Walla Walla, generally do better in Northern states and the short-day types, like Yellow Granex and Red Burgundy, should be planted if you live in the South. Plant your onion seed indoors in February so that you can plant your seedling in the garden in April.
Fill the planting pot with seed-starting mix, to within 1/4 inch of the top. Water the soil well and allow the excess water to drain from the bottom of the pot.
Push the onion seed into the soil, 1/4 inch deep.
Spray the soil lightly with a plant misting bottle to maintain the soil's moisture when the surface appears to be drying.
Place the planting pot in an area that gets lots of sunshine and remains at a temperature over 75 degrees F. Your seed should begin to sprout within five days.
Plant your onion plant in a sunny spot in the garden when it reaches 6 inches in height.