Walla Walla
Bulb Onion in the US

Now, getting these started from seed is the way to go, as you rarely see them as plug plants. The key is timing, and that really depends on your USDA zone. If you're in a colder spot like Zone 3 or 4, you're looking at April or May. Zones 5-7 can sow February to April, while Zones 9-10 can go as early as January or even late in the year. Sow seeds about half an inch deep, either indoors in trays for transplanting later, or directly into the ground once the soil warms up. Give them about an inch spacing in the rows to start with.

If you started your seeds indoors, once they're big enough to handle, about three or four inches tall, you'll want to prick them out and give them a bit more space in their trays. Then, before they go into the ground permanently, you've got to harden them off for a week or two – gradually getting them used to the outside weather, you know. Plant them out about four to six inches apart in rows that are a foot apart, once all danger of hard frost has passed for your area.