Drying seeds

The majority of the world's seed-bearing species produce ‘orthodox’ seed that can be dried and then frozen. Under most circumstances, both drying and freezing increase the longevity of the seed.

The initial drying room where seeds are placed on arrival (Image: RBG Kew)

The air within the drying facility or room is chemically dried to 15-18°C and 15% relative humidity. The dry air gradually ‘pulls’ moisture from the seed until equilibrium is achieved where there is no net movement of moisture either into or out of the seed (usually this takes less than a month). 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 container types 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 project.