Over 2 billion seeds are stored at RBG Kew’s Millennium Seed Bank (MSB). It is crucial that the collections are preserved correctly to maximise their lifespan and enable their use in research and conservation for generations to come.

Some seeds can persist for a long time in the soil. We see this when plants appear following soil cultivation which brings the buried seeds to the surface. However, under ideal storage conditions, seeds can survive for much longer; hundreds or even thousands of years. The environment at the MSB is finely-tuned to provide the best conditions for seeds to stay alive for as long as possible.

By reducing seeds’ internal water content, biological processes are halted, fixing them in time. It has been known for centuries that grains last much longer when dried, and this knowledge has been harnessed and developed by decades of research at the MSB and elsewhere to extend seed lifespan. We now know that reducing a seed’s moisture content by 1% doubles its lifespan, so at the MSB we dry the seeds in rooms maintained at 15% relative humidity…much drier than typical indoor humidity. Seeds of about 90% of seed-producing flowering plants can be safely dried in this way before storage.
However, the remaining species produce seeds which cannot survive the harshness of drying. For these species, alternative methods including cryotechnology, where liquid nitrogen is used to create super-chilled storage conditions, can be effective. These species may also be conserved as living plants in botanical gardens like Kew.

Before any seeds are stored long-term, they must be cleaned by removing debris and any insects or fungal spores within the collection. Due to the broad diversity in seed structure, much of this cleaning has to be done by hand as no one size fits all! Every seed is valuable as it may contain unique genetic characteristics that could help it survive in the wild, so careful cleaning is vital to ensure none are damaged or lost. X-ray imaging is the final stage of cleaning and is a quick way of checking whether the inside of the seeds look healthy without cutting them open.

When we’re sure that seeds are as clean as possible, it is time to bank them! Each collection is divided into two portions which are stored separately and have different purposes. The ‘active’ portion is used for conducting research or routine seed quality testing. The ‘base’ portion, however, is only intended to be used when the seeds are to be returned to the wild in conservation projects and can remain untouched for decades!

The storage vaults at the MSB are kept extremely cold. This is because chilling, along with drying, is an important factor in extending seed lifespan. Although managed for temperature, the frozen vaults are not humidity-controlled, so a good protective seal on seed storage containers is key to maintaining low seed moisture content during storage. We use preserving jars with rubber seals - the same as those used for food storage - as they are very effective at keeping moisture out whilst enabling us to see the seeds inside.

At a freezing -20°C you may not think it, but due to the huge variety of species in storage, the MSB’s underground vault is the most diverse place on Earth! In our next blog post, we’ll share some of the tricky germination challenges facing us when we take seeds out of the bank for their use in restoration projects, with a focus on threatened Red hemp-nettle, a primary target plant species for Colour in the Margins.

Sarah Pocock

UK Native Seed Hub Assistant - MSB.