Seeds in cold storage
Once the seed has been dried to equilibrium with 15% relative humidity it is sealed in a glass container and placed in a cold room where it is kept at a temperature of -20°C. A small sachet of silica gel impregnated with an indicator that changes from orange to green when moist, is placed in each container to monitor the effectiveness of the container seal during storage.
As an extra precaution, small samples from high conservation priority collections or from species expected to be short-lived are also stored in liquid nitrogen vapour at approximately -196°C.
The length of time that each collection can remain alive depends on the species. Some seeds may live for only a few decades, others for centuries and, in some cases, even millennia.