I like to use old seed as long as I can. My last two plantings, I’ve seeded single pots of my old seed to see if it’s still viable. I’m labeling and keeping track of it. I have Seed from 2009 to 2017. The 2009 seed is 8 years old! No doubt dead. I think this will give me a sense over time of how long I am able to save different types of seed. It’s also a plain old test of the old seed. If it doesn’t germinate, I toss it.
The seeds I sow early are particularly important to be viable. For seed like celeriac that takes a week or so to germinate, and also onions that germinate faster but still take time to grow, I don’t want to find out in April that my seed was too old.
If I have lots of viable old seed then I’ll get a bumper crop if seedlings and more to share. And I’ll save the seed and give it a try again next year.