If you missed them, you may want to begin with my earlier reports on my tour of the Millennium Seed Bank – seed arrivals and seed storage.

If you’ve ever looked at an old packet of seeds and worried that they may be past their best, or been annoyed when the seeds you’d sown didn’t germinate, then spare a thought for the scientists at the Millennium Seed Bank – the fate of endangered plants everywhere rests on their shoulders!

We’ve already seen how they process newly arrived seeds, clean them up and dry them out and send them down to the vault for long term storage. But that’s only the first half of the problem; we need to know that those seeds will still be viable when we need them.

Seed germination rates are very variable anyway, and the staff at Kew have a big computer database in which they record all kinds of germination information. Not only does that help them germinate seeds with which they are familiar, but it also helps to predict the conditions under which unfamiliar seeds may germinate (species in the same plant family, or from the same geographical region may germinate under the same circumstances).

(For more information on seed viability, and how to test the germination rates for your own seeds at home, read chapter 1 of The Peat-Free Diet.)

Germination testing

To ensure that seeds remain viable, every ten years a sample is taken out and tested for germination; some seeds may be grown on into plants, from which fresh seed is then saved. Many seeds respond to fairly standard treatment, and germinate on plates of agar jelly, filter paper or damp sand. They have a lovely germination ‘closet’:

Germination test room

They also suffer the same problems with mould that gardeners do – if they need seedlings then the germinated seeds are pricked out and potted up as soon as possible.

Ovens and fridges

Some seeds need darkness to germinate (and are covered in tin foil!), others respond to light. Some expect to be treated roughly – scarification – or need their seed coats etched with acid. Others still need to be exposed to smoke, or heated in an oven. A wall of ovens and fridges set to different temperatures accommodates even fussy characters who need several cycles of different temperatures to encourage germination.

Plant families known to be reluctant to germinate outside of their natural habitat are assigned a scientist buddy, who becomes an expert on their needs and stands the best chance of achieving germination successfully. Research into germination factors is ongoing.

Cacti

Plants are grown in the attached greenhouse, under ideal conditions, so that they flower and set fresh seed.