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Zurich Seed Bank

A Local Seed Vault to Boost Biodiversity

Researchers at UZH are freezing the seeds of threatened local plants to help increase the biodiversity of ecosystems in the future.
Patrizia Widmer; English translation by Philip Isler
We accompanied Gregory Jäggli and Simon Gysi as they searched for, cleaned and froze the seeds of threatened plants.

The basic premise of the Zurich Seed Bank is very simple – collect the seeds of threatened plants species, dry them and freeze them for use in the future. The goal is to preserve the seeds of threatened plant species for posterity so that it will one day be possible to reuse them to boost local biodiversity.

Biodiversity has been declining in Switzerland for more than a century. Entire plant communities are disappearing, fueled by the loss or fragmentation of habitats, pollution, invasive species and climate change.

Nature preservation organizations in Switzerland and abroad have been warning us about the consequences of biodiversity loss, calling on all of us to take action before it’s too late. This is exactly what the team at the Zurich Seed Bank intends to do. The team is made up of project leader Gregory Jäggli, academic head Michael Kessler and a number of volunteers. Watch the video to find out how the seed vault works.

University project with Swiss-wide significance

The Zurich Seed Bank is a conservation project created by the Department of Systematic and Evolutionary Botany at the University of Zurich. Thanks to the project, seeds of threatened local plant species have been stored in freezers at the department, located right next to the Botanical Garden, since 2021. The precious seeds can one day be used to reintroduce certain plant species, strengthen existing populations and conduct research. The seed bank aims to collect seed samples for as many of the vascular plants listed on the IUCN Red List of Threatened Species as possible in order to preserve biodiversity and safeguard genetic diversity.

Need for seed

The decision to add a plant’s seeds to the vault is based on how endangered the species is.  Before Jäggli and his team of volunteers venture out into the field, he first needs to conduct research and analyze plant occurrence reports to find out where the species can be found.

Once the seeds are ripe, the collectors get to work. This is easier said than done, however, as there is very little literature on when the seeds of individual plant species actually become ripe. Collect seeds that are unripe, and they’ll perish. Arrive at a plant population too late, though, and the seeds will already have fallen off the plants. This is why team members usually need several visits to a site to make sure that the seeds are collected at the right moment.

The art of seed conservation

For certain populations, harvesting seeds can be tricky, says Jäggli with a smile. “It’s easy to find a species when it has nice-looking flowers. But when all that’s left of a plant is a few brittle stems, it can be difficult to find it again.” Farmers unexpectedly cutting down meadows also may also complicate things.

If everything goes according to plan, the volunteers ideally collect between 10,000 and 20,000 seeds per species. They take no more than a fifth of available seeds – any more would jeopardize the plants’ ability to reproduce naturally – and bring them to the seed bank, where Jäggli takes charge of them. At the bank, the seeds are cleaned of other plant parts that would interfere with the freezing process. When it comes to dandelions, for example, Jäggli has to remove every single one of the fluffy parachutes from the sample. For some plant species, a machine helps him prepare the seeds, while for others, he has no other choice but to do so by hand – a time-consuming process.

After this step, the seeds are dried until their moisture level drops to around 5%. This slows down the aging process and makes them easier to freeze. If the seeds are too moist when they’re frozen, ice crystals will form on the inside, which would destroy the seed. Finally, the seeds are frozen at -20°C. Frozen seeds can be kept alive for decades or even centuries. However, this doesn’t work for all plants. Around 95% of Swiss plant species have seeds that are resistant to desiccation, while the other 5% perish when desiccated.

Insurance policy

Jäggli tests the seed samples he receives to make sure they’re intact and able to germinate. The biologist also conducts regular germination tests once the seeds are frozen to be able to take action in good time should their ability to germinate deteriorate. These tests allow Jäggli to shed light on the conditions under which various plant species are best able to germinate, providing crucial information that boosts the success rate of reintroduction projects.

To ensure that the seeds remain intact over a long period of time, he seals the seeds in double-walled glass containers that have a system to indicate moisture: the tiny silica beads inside the containers change color if they become moist. In addition, the freezers are connected to an alarm that goes off when the temperatures changes. Jäggli also sends seed samples of each plant species to the seed bank in Geneva – an insurance policy, so to speak, in the unlikely event that all these safety measures fail.

Big plans

The genetic makeup of plant species differs depending on where they’re found. This is why Jäggli has plans to collect and freeze plant seeds from up to five different populations from all over Switzerland to preserve as much of this genetic diversity as possible. To make this happen, he intends to work with volunteers from across the country.


A nation-wide project is also set to launch next year, in which professional collectors from across Switzerland will harvest seeds from the wild relatives of our current crop plants on behalf of the Swiss Federal Office for Agriculture. Many of these wild plants feature on the red list of threatened species. The project aims to crossbreed the wild plants’ resistant genes into our crops to make the plants more resistant to disease and drought.

For now, the Zurich Seed Bank’s focus is on collecting and freezing seed samples. In the future, however, once enough seeds are stored and additional staff have been hired, the focus will turn to reintroduction projects – in cooperation with environmental offices and the Swiss cantons.