Citizen Science – The Garden Experiment
Citizen scientists are helping us understand the science behind restoring healthy soils
Soil is alive. Beneath our feet, billions of microorganisms form complex communities that play a vital role in plant growth and health. Some soil bacteria interact with plant roots, promoting nutrient uptake, stimulating plant growth, and helping plants resist disease. Yet soil biodiversity is declining worldwide, making it increasingly important to find new ways to restore healthy, diverse microbial communities.
One of NCCR Microbiomes’ long-term goal is to develop strategies for restoring degraded soils by introducing beneficial microbial communities from healthy soils. In principle, transplanting diverse microbes could help re-establish a balanced soil ecosystem and improve soil health.
Before this approach can become a practical restoration tool, however, we need to answer a fundamental scientific question: what happens when two different soil microbial communities are brought together? Do the introduced microbes establish themselves, or are they outcompeted for nutrients and space by the microbes already present? Understanding these interactions, known as microbial community coalescence, is an essential first step towards designing successful soil microbiome transplants.
This is where citizen scientists make an invaluable contribution.
The citizen science experiment
In September 2025, more than 200 volunteers across Switzerland took part in our experiment. Participants used their own gardens, whose soils provide a wide range of naturally occurring microbial communities to study community coalescence. Each volunteer received a soil inoculum prepared from natural soil collected at the University of Lausanne, where the microbial community had been carefully characterised.
Participants mixed the inoculum into a small area of garden soil and left it undisturbed for six weeks. They also collected a control sample from the same garden that did not receive the inoculum. By comparing the microbial communities in the treated and untreated soils, we can determine which introduced bacteria established themselves and how they interacted with the resident microbial community.
To ensure the experiment was carried out consistently across all gardens, participants received detailed written instructions and a step-by-step protocol video. Throughout the project, we stayed in touch through regular newsletters, sharing updates on the progress of the study and explaining the next stages of the analysis. We also had the opportunity to meet many participants in person to present the first results and discuss the project together. This ongoing exchange between researchers and volunteers was an important part of the citizen science experience and helped make the project a true collaboration.
Although each volunteer carried out a simple experiment, together they created a large-scale study spanning hundreds of different gardens and soils. This diversity provides an ideal natural testing ground for understanding how microbial communities merge and compete. The knowledge gained from this experiment will help lay the scientific foundation for developing microbial transplant strategies that could one day be used to restore degraded soils.
Science et Cité made a short video about this experiment:
In July 2026, we shared the results of the experiment with all the participants.
Each volunteer received a personalised summary of their garden soil data, including:
- The nutrient levels (carbon and nitrogen) and pH of their soil.
- The composition of the soil microbial community.
- An overview of the collective results from all participating gardens.
The project does not end here. We are combining these results with those from a complementary citizen science experiment carried out with our colleagues in Japan.
In autumn 2026, we will use these combined findings to prepare a scientific manuscript for publication in a peer-reviewed journal. As with the individual results, we will share the published study with all participants once it becomes available.