Tips for planting onions include choosing the appropriate varieties for the region in which you live, following proper spacing and planting them in rich, organic soil. Onions are available in many varieties, but the plants must have sufficient time to develop before the lengthening of the days due to the Earth's tilt signals them to begin forming bulbs. In northern latitudes, red, white and Walla Walla sweet onions are a good choice.
When planting onion seeds, place them at 1/2-inch intervals, and cover them with an inch of soil. Once the seeds sprout, thin them to 4- to 6-inch intervals that allow room for the bulbs to grow to maturity. If you plant onion sets, which are seeds that have sprouted into plants approximately 4 inches tall, space them using the larger spacing, eliminating the need to thin plants later.
Prepare the planting beds for onions by working 2 to 4 inches of well-rotted manure or compost along with up to 2 pounds of complete fertilizer per 100 square feet into the soil. Avoid using sulfur based fertilizer on onions if possible. Sulfur makes the plants more pungent. Read the ingredients labels on the fertilizer, and choose those containing ammonium nitrate over those containing ammonium sulfate whenever possible.