With seeds, how old is too old?

[HopeHoops]

6. Legumes - never if they are kept dry. Squash, about 3 years. Nightshades at least 10.

I've never had old lettuce-type seeds not sprout, or radishes for that matter. Root crops also tend to come up regardless of age. You'll get decreasing germination rates for most seeds, so the older they are the closer you need to plant them. It can also help to soak them overnight before planting day.

I'm still using radish and lettuce seeds that I know are at least 20 years old. I plant them everywhere in and around the other plants because they produce HUGE fibrous root systems that remain in the ground when you pluck them. It adds organic material. Radishes are also great for marking rows. The sprouts are probably the easiest thing to identify and usually come up within a week. Just mix them in with carrot or other slow-to-sprout seeds and the row will be easy to distinguish from weeds.