How long can a seed stay alive?

There are no definite answers here. From the research done by conservationists, the durability of a seed is known to depend critically on how it is stored: keep it in ultra-cold, dry conditions and you can expect it to stay alive for several hundred years.

Which makes this week's story from Israel, that scientists have grown a date palm from a 2,000-year-old seed found during archeological excavations on Mount Masada, seem extraordinary. The Israeli team say the age of the date palm seed was verified by radio carbon dating.

But it's not the only ancient seed to have germinated: in the mid-1990s, a Chinese lotus plant grew from a seed that was dated at around 1,400 years.

At the Millennium Seed Bank - a leading centre for long-term storage of seeds, based at the Royal Botanic Gardens in Kew - initially, seeds are usually dried to between 4% and 6% moisture content. Then the seed is kept at -20C. "For all the wild species that live on our seed bank, we estimate that for most species we're certain of many hundreds of years [of survival]," says John Dickie, of Kew's seed conservation department, which runs the seed bank.

The only way to check how long seeds really survive is to plant them in a few hundred years' time. A more practical method is to use a mathematical model, which projects what botanists know about seed survival into the future. Dickie has found that if wheat grains are kept at a constant 16C, one grain in a thousand might germinate after 236 years. With temperatures in the high 20s, the grains would all be dead in 89 years.

The Chinese lotus plant survived so long because its seed would have been impervious to water and, by falling to the bottom of the lake in which it was found, it stayed relatively cold.

But, according to Dickie, surviving two millennia in the desert soil of the middle east stretches the imagination. "I would have thought the average temperature is working against you," he says. "I have not seen the [date palm] work written up in a scientific journal. I maintain a bit of scepticism."

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