Hi Wolverine -

You should start onion seed about 12 weeks inside prior to setting them out. Onions are frost-tolerant so they can be set outside as long as it won't have a hard-freeze.

I did some viability testing on my seeds last weekend - Copra onion seed that I received in January is still good; 18 out of 18 sprouted 11 months later. I'm a good 1.5 months early before starting onion seed inside, but I'm going to see if I can baby these onions and keep them around until April when I'll put them outside. Always seem to be doing some kind of experiment.

The earlier you can get the seeds set outside, the better. That is because around June 21st is the summer solstice and after this point, onions no longer will produce their "leaves" but begin bulbing. The more "leaves" they have, the larger your bulb will be.

Here is a link that might be useful: BsnTech Gardening Blog

The onions I planted from seed last Feb and transplanted into my Kenai, AK garden in May were still producing leaves the end of Sept when I had to finally pull them. Only a few had 'bulbed'. I'd like to plant some more from seed, but need a variety that will 'bulb' and not just go on enjoying the weather! :)

In Zone 6, i start my onions, Leeks, and Shallots anytime in Mid-January to end of February.