The majority of the world's seed-bearing plants produce ‘orthodox’ seeds that can be dried to a low moisture content and then frozen. Drying, sealing and freezing will often lead to at least a 100-fold increase in seed storage life.
The initial drying room where seeds are placed on arrival (Image: RBG Kew)
Air dried using desiccant-impregnated dryers to 15% relative humidity is fed into the initial dry room which is maintained at 15oC. Seeds lose water to this dry air by diffusion until they are in equilibrium, a process that can take from a few days to several weeks depending on the size of the seeds and other physical characteristics. When equilibrium has been achieved, the seed is checked for dryness by non-destructive means using a hygrometer. Once dried and processed, the collections are packaged in a variety of different air-tight containers prior to sub-zero storage.
Kew’s Millennium Seed Bank has two drying rooms – one for receiving the collections on arrival prior to cleaning, and one located next to the cold rooms in the seed vault, for the final drying prior to storage. Alternative means of drying seed are also being investigated by the Millennium Seed Bank Partnership.
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