I don't think there is a guarantee. what you can do is try a test germination. It is a fact that alliums lose viability very quickly, as compared to many other vegetables. I have had pretty good germination rate with 3 years old leeks. I think in part it depends how the seeds were kept.

I always get excellent germination from 1st year seeds and decent germination from 2nd year seeds, but I toss anything more than two years old. This year I've finished off some 2012 seeds, seeing about 60 percent germination compared to 80 percent or more from fresh seeds from Johnny's, Fedco or Southern Exposure.

2 years is the limit. I agree.

Fresh seeds are the key I'm finding out, replanted with new seed packs and sprouts are coming up after 4 days on a heat mat. Thanks all.

You don't need a heat mat for onion seeds.

Thanks Minnie, I had no idea, probably burning my onions up!