What can tea bags tell us about soils?

By burying ordinary tea bags we can gain knowledge of how actively and efficiently the soil breaks down (tea) leaves and plant parts, which shows how quickly the soil can convert organic material into nutrients and soil. By burying tea bags (of a specific type), you can contribute to our knowledge about decomposition, soil health, and the global carbon cycle.


On this page, you can learn about:

  • Decomposition, soil health and the global carbon cycle
  • What is the Tea Bag Index (TBI) and how does it work?
  • The researchers involved in the project
  • How YOU can participate.

What is decomposition?

Decomposition is the process of organisms digesting plant material in the soil. That is, a leaf falls from a tree, lands on the ground, and turns into soil. The fresh soil provides nutrients to the tree, which then grows new leaves. Decomposition is therefore part of the nutrient cycle and fundamental for life on our planet. Through this process, dead plants and other organic material become “food” for plants and organisms living in the soil.


“Decomposers" are the tiny organisms, like nematodes, fungi and bacteria, breaking down organic material and turning it into soil. A teaspoon full of healthy soil contains hundreds of nematodes and millions of bacteria. These microorganisms depend on various environmental factors to survive and thrive, which dictates the speed of decomposition.


The speed of decomposition depends on:

  1. Environmental factors (moisture, acidity, temperature and nutrient levels in the soil). These factors influence how active the microorganisms are and how much they can eat.
  2. Chemical properties of the material (e.g., a wooden branch compared to a flower) Just like us, microorganisms prefer certain foods over others. They like sugar but are not as fond of harder materials like wood.
  3. Types of decomposers. Mites, worms, fungi, and bacteria all break down different plant materials at varying rates.

All organic material consists of mixtures of easily decomposable materials (such as sugars in leaves) and materials that are harder to break down (for example lignin in wood). Because of this, decomposition occurs in two different phases.


In the first phase, all easily decomposable material is broken down, and the decomposition rate is fast. During this part of the process, a portion of the easily decomposable material is transformed into harder-to-break-down material – this is called stabilization. In the second phase, only the hard-to-break-down material remains, as this was barely decomposed during the first phase and the decomposition rate is very slow. The speed of each phase depends on the three factors mentioned above (environmental factors, chemical properties of the plant material, and the types of decomposers).

The Tea Bag Index Method

Since tea consists of plant material, it can be broken down by microorganisms. This means that tea can be used to investigate the decomposition capacity of the soil. When dead plants break down, their weight decreases. By first weighing and then burying tea bags, we can examine how the content inside the bag (the weight of the tea) is affected over time. This method is called Tea Bag Index (TBI), and it has been developed by researchers at the University of Utrecht, Umeå University, the Netherlands Institute of Ecology, and the Austrian Agency for Health and Food Safety Ltd.


The TBI method uses two types of tea: Green and Rooibos tea. Green tea mainly consists of materials that can be easily decomposed by microorganisms, while Rooibos tea is more woody and contains a smaller proportion of easily decomposable material. Therefore, Roobios tea decomposes at a slower rate than green tea. By comparing the decomposition of green and red tea, we can gain knowledge about why the decomposition of a twig and a leaf differs at a particular location. This, in turn, can increase our understanding of what drives the carbon cycle and how changes in the environmental conditions will affect carbon dioxide emissions.


First, the weight of the tea bag is measured and then the bag is buried and left underground for three months. The small holes in the tea bags allow microorganisms to break down the tea inside. Since the tea types consist of different materials, green tea will decompose quickly, while the Rooibos tea will still be in the "first phase" of decomposition after three months. This will result in different weights of the remaining tea.


When the tea bags are recovered, primarily hard-to-decompose material remains, but some easily decomposable material that has stabilized is also present. By weighing the tea bags before and after burial, we can gain knowledge about the different phases of decomposition.


The TBI method makes it easy to compare different locations in a standardized way. It helps researchers to investigate how the climate and other environmental factors affect decomposition. At the same time, the TBI method can be used to educate students about decomposition, soil health, and the importance of taking care of our planet.


About the Website

Since the development of the TBI method, hundreds of researchers and thousands of schoolchildren and citizen scientists have helped bury tea bags and report their results. In the Tea Tales project, we have transformed the co-created database into an interactive mapping tool where anyone can upload their results, download selected parts of the database, compare decomposition between different locations, habitats, and time periods, and deepen their knowledge of decomposition and soil health.


On the website, you can also explore stories in the form of video clips, images, and illustrations from (citizen) scientists around the world and stay updated on upcoming events in TBI research. Tea Tales is a collaboration between Public & Science, VA, Hushållningssällskapet, and researchers at Umeå University. The website is co-created with teachers, gardeners, and farmers.


Do you want to bury tea bags?

Anyone can participate in burying tea bags and reporting their results. Whether you are a researcher, farmer, hobby gardener, teacher, student, or just curious, you can help. Here you can find instructions, and for teachers, there is a special teacher's guide!

  • Skärmavbild 2022-11-22 kl. 10.58.50

    Taru Sandén (former Lehtinen)

    Senior expert, Austrian Agency for Health and Food Safety 

    Taru Sandén is a soil enthusiast who enjoys working with various stakeholders and leads the teaTime4Schools project. Taru is involved in development of the teatime4science app. 

    More info  

  • Skärmavbild 2022-11-22 kl. 11.00.09

    Judith Sarneel

    Associate professor, Department of Ecology and Environmental science, Umeå University 

    Judith Sarneel is an enthusiastic spatial ecologist that studies decomposition and vegetation change, and leads the Teatime4science project. 

    More info 

  • Skärmavbild 2022-11-22 kl. 11.01.04

    Sarah Duddigan

    Lecturer in Environmental Science, Department of Geography & Environmental Science, University of Reading

    Sarah Duddigan is a keen soil scientist who has worked with lots of stakeholders including farmers and gardeners. She ran the Tea Bag Index-UK citizen science project. 

    More info 

  • Skärmavbild 2023-11-20 kl. 16.16.14

    Janna Barel

    Researcher, Radboud University

    I want to know how the relationships between plants and soil organisms influences the functioning of peatlands in a changing climate 

    More info

  • Skärmavbild 2022-11-22 kl. 10.53.30

    Sarah Schwieger 

    Post doc, Climate impact Centre, Umeå University 

    Sarah is a plant ecologist with a strong focus on belowground ecology. She aims to understand how decomposition and soil respiration are affected by the many factors that change with climate warming, such as temperature, precipitation, and plant species composition.  

    More info