According to The UK Centre for Ecology and Hydrology, just one teaspoon of soil contains approximately one billion individual microorganisms. This is equivalent to one eighth of the planet’s entire human population.
Leading researchers indicate that these microorganisms are having significant impacts on our health and wellbeing.
In a global assessment published by the Food and Agriculture Organization of the United Nations (2021), it was reported that ‘soil is the key link in the functioning of ecosystems’, with soils having a considerable impact on ‘the quality of the food we eat, the water we drink, and the air we breathe’.
And, it is theorised by microbiological researchers, soils can subtly contribute to shaping our mood – and not just our physical health. As Professor Tomás Villa (2021) writes in the journal Springer, soils include ‘mood-altering microorganisms’ that can promote both ‘happiness or aggressive behaviour’.
So, it appears, getting down and dirty can actually help us with our mental state. Horticultural therapy recognises the fundamental importance of gardening, soils and plants and is gaining visibility across Australia.
A 2023 study from public health expert, Phi-Yen Nguyen, published in The Lancet Planetary Health, found that horticultural therapy improved symptoms of depression and anxiety. Western Sydney researcher Astell Burt (2023) cites ‘nature prescriptions’ as lowering risks of depression, anxiety, and high blood pressure.
Additionally, in 2024, Charles Darwin University introduced the first Australian accredited course aimed at helping ‘nature therapy bloom’ in Australia, for benefits to both mental and physical health.
And, with urban gardening and horticultural therapy being recognised as an affective gateway to improved mental health, starting a garden has become a natural route for enriching one’s own wellbeing.
Healthy soil, healthy mind
The green spaces our bodies and minds rely on are directly dependent on soil, as soil affects the mind in ways that extend far beyond physical contact.
This correlation between mental health and soil is mechanically simple with soil researcher, Winfried Blum (2019) noting that, ‘direct contact’ with the diverse range of microbes in the soil impacts our personal microbiome, with soil acting as ‘a major inoculant and provider of beneficial gut microorganisms’.
A recent study from the National Library of Medicine by Amjad Mhanna (2024) has shown that microbes in the gut are responsible for the production of hormones such as serotonin, which are key moderators of both mood and behaviour. And, connecting with healthy soil organic matter supports a diverse gut microbiome, culminating in improved mental health and overall wellbeing.
This soil-soul connection is known fondly as ‘dirt therapy,’ and gardening is proving to be an effective tool for natural relaxation and reconnection in urban environments. The Melbourne International Flower and Garden Show (2025) reported that 60% of Australians showed improvements to mood and calmness after spending time among plants.
Some challenges
While gardening can support our mental wellbeing, urban soil contamination poses a challenge to this natural therapy.
Australian scientists and researchers are having to keep their fingers on the pulse of urban soil health and decontamination as contaminants are noted as a major threat to Australian soil by the Institute for Australian soil (2014). Research found more than 160,000 sites across the country are polluted with as many as 75,000 different contaminants.
Soil scientist Salar Rezapour (2022) found that accelerated urbanization across Australia has led to toxic buildup of ‘heavy elements’ in urban soils, depreciating soil health and by extension, the therapeutic potential of gardening.
This needs to be put in context with a recent study by Simon Masson in Springer Nature (2025) arguing the potential of urban soils as hotspots of microbial diversity, not solely from a taxonomic but also from a functional point of view. This highlights that human management practices and interventions can contribute to sustainable soil outcomes.
Additionally, Masson found that while soil is the likely home for approximately 59% of Earth’s species, its biotic diversity is still largely unexplored. And, social awareness of these crucial ecosystem services and the potential risks provided by soil remains very low for both citizens and professional workers as gardeners.
The health of our earth and our mind may be more linked than we had imagined, with the seeds in our gardens silently sowing mental serenity.
Article by Christian Nevin
References:
Astell-Burt, T., Hipp, J. A., Gatersleben, B., Adlakha, D., Marselle, M., Olcoń, K., Pappas, E., Kondo, M., Booth, G., Bacon, S., Lem, M., Francois, M., Halcomb, E., Moxham, L., Davidson, P., & Feng, X. (2023). Need and Interest in Nature Prescriptions to Protect Cardiovascular and Mental Health: A Nationally Representative Study With Insights for Future Randomised Trials. Heart, Lung and Circulation, 32(1), 114–123. https://doi.org/10.1016/j.hlc.2022.11.008
Blum, W. E. H., Zechmeister-Boltenstern, S., & Keiblinger, K. M. (2019). Does Soil Contribute to the Human Gut Microbiome? Microorganisms, 7(9), 287. https://doi.org/10.3390/microorganisms7090287
FAO and UNEP. (2021). Global assessment of soil pollution: Report. Chapter 4: Soil pollution and risk to human health. FAO and UNEP. https://doi.org/10.4060/cb4894en
Masson, S., Matteo Chialva, Bongiovanni, D., Adamo, M., Stefanini, I., & Lanfranco, L. (2025). A systematic scoping review reveals that geographic and taxonomic patterns influence the scientific and societal interest in urban soil microbial diversity. Environmental Microbiome, 20(1). https://doi.org/10.1186/s40793-025-00677-7
Mhanna, A., Martini, N., Hmaydoosh, G., Hamwi, G., Jarjanazi, M., Zaifah, G., Kazzazo, R., Mohamad, A. H., & Alshehabi, Z. (2024). The correlation between gut microbiota and both neurotransmitters and mental disorders: A narrative review. Medicine, 103(5), e37114–e37114. https://doi.org/10.1097/md.0000000000037114
Nguyen, P.-Y., Astell-Burt, T., Hania Rahimi-Ardabili, & Feng, X. (2023). Effect of nature prescriptions on cardiometabolic and mental health, and physical activity: a systematic review. The Lancet Planetary Health, 7(4), e313–e328. https://doi.org/10.1016/s2542-5196(23)00025-6
Rezapour, S., Siavash Moghaddam, S., Nouri, A., & Khosravi Aqdam, K. (2022). Urbanization influences the distribution, enrichment, and ecological health risk of heavy metals in croplands. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-07789-x
UK Centre for Ecology & Hydrology. (n.d.). Why do soil microbes matter? Natural Environment Research Council. https://www.ceh.ac.uk/our-science/case-studies/case-study-why-do-soil-microbes-matter
Villa, T. G., & Sánchez-Pérez, A. (2021). The Gut Microbiome Affects Human Mood and Behavior. Springer EBooks, 541–565. https://doi.org/10.1007/978-3-030-77595-7_22