A man named William James Beal started an experiment in 1879, which has become the longest-running test of seed dormancy in soil.
Beal buried twenty bottles containing sand and seeds from twenty-one common plants. He buried the bottles eighteen inches underground, uncorked to allow in oxygen, and upside down to prevent water from accumulating in the bottles and drowning the seeds. The experiment was designed to test how long these various seeds could survive under virtually natural conditions before they would lose their ability to produce a plant.
Seed dormancy is why some seeds wait for the correct season before they germinate. They're programmed to wait for conditions suitable to the plant's survival. Seed dormancy is also why weeds are never-ending nuisances. Weed seeds can lurk underground unseen, and then when you till soil to make way for a flower bed, the seeds awaken and before you know it, your flower bed is overrun with the pesky weeds.
Most of the seeds in Beal's experiment were still viable after ten years, but as time passed, fewer and fewer of the seeds would germinate. The fifteenth of Beal's twenty bottles was dug up in 2000, 120 years after it was buried, and two species were successfully germinated--moth mullein and a mallow called cheeses. These are also the same two species that grew from the fourteenth bottle in 1980.
The plant that holds the record for the longest dormancy is a lotus that was sprouted in 1995 from a seed that radiocarbon dating estimated to be a whopping 1300 years old. Now that's one stubborn seed.