Microbes, our greatest allies in the garden, by Selwa Calderbank
When Selwa approached me to write an article about microbes and gardening at the beginning of the year, I was interested. She had been speaking to Jake Robinson (a microbiologist who has worked in the field of ecological conservation and whose book Invisible Friends: How Microbes Shape Our Lives and the World Around Us is due out this month) and was full of enthusiasm and fascination for this mind-expanding topic. It immediately brought to mind Ed Yong’s book from 2016, I Contain Multitudes, which focussed on microbes and the animal kingdom. I was keen to hear about the subject from an ecological conservation/botanical/gardening perspective.
Microbes are everywhere, all around us, in numbers we find it hard to comprehend. They are integral to life. Learning more about them and appreciating them creates the possibility of shifting our perspective of the world and our place in it. I particularly like how they trouble our notions of individuality. What does it mean to be an individual, human even, when we are teeming with microbes? As Yong tells us, we each have more bacteria in our guts than there are stars in our galaxy. We are not so self-contained or separate as we like to think. Our very existence comes from evolving, symbiotically, among and from microbes.
Microbes, our greatest allies in the garden, by Selwa Calderbank
Microbes have had some negative press in recent times. The Covid-19 pandemic and the drastic effect it had on our lives has led many of us to see microbes as ‘germs’ to be avoided at all costs. But whilst some microbes do transmit disease, many are our greatest allies, benefitting our immune system, our gut health and our mental health. And we can nurture them in our gardens and green spaces, and maybe even in our cities, to maximise our exposure to their health-giving properties.
Jake Robinson is a microbiologist who has worked in the field of ecological restoration. I talked to him about the incredible benefits of the microbiome for human health, and especially how we as gardeners might better understand the complex ecosystem linking us with the microbial communities that thrive in healthy, biodiverse soils and vegetation.
Old friends in our gut
Our interactions with microbes goes back to our origins as a species. In what is known as ‘the old friends hypothesis’, scientists believe that our symbiotic relationship with the microbiome comes from our intimate connection with the rest of the living world as hunter-gathers. We absorbed beneficial microbes from our environment and they became a part of us, living in our gut and supporting our health. We still need these invisible old friends, but unfortunately the way we now live has divorced us from our natural environment, and greatly reduced our exposure to healthy microbial life. Researchers believe this could be at the root of the explosion in auto-immune illnesses and allergies afflicting so many people in the modern age.
Robinson’s ecology background and academic interest in molecular biology led him to examine how spending time in natural environments can improve human health. We all probably know by now that spending time in nature is good for us, but how do we measure that at the invisible level? One way is to track the time people spend in the natural environment, being exposed to the microbiome, and then examining their skin microbiome. It involves looking at what is in the environment already, whether it transfers to humans and if that transfer changes the microbiome within humans, and finally whether that change affects our immune systems.
Forest materials and health
Some compelling research from Finland shows just how important it is for us to reconnect with the healthy and biodiverse invisible life around us. In a recent study, urban day-care children were exposed to forest materials and undergrowth, like blueberries and heather, and were allowed to care for crops in containers in their outdoor play space. The diversity of microbes in the guts and on the skin of these children appeared healthier and more diverse within just 28 days when compared to other children who played in paved over day-care spaces. A two-year follow-up showed that the beneficial immune effects were still present in the children exposed to forest materials two years later. Studies seem to highlight the importance of early exposure to biodiverse green space for a well-functioning immune system.
It's not just our general immunity that benefits from a healthy microbiome. It could also have a positive impact on our mental health. In an Australian study, healthy soil from a biodiverse natural environment had an incredible effect on mice. They were exposed to trace levels of soil – some from low and some from high areas of biodiversity. Those exposed to the more biodiverse soil showed clear reductions in anxiety. The more biodiverse soil contained bacteria that produce short-chain fatty acids, in particular one called Butyrage, which regulates inflammation in our bodies. This in turn is thought to impact mental health. Researchers in this study suggest that we could design green spaces to enhance human health, and even integrate biodiversity into healthcare.
Healthy soils and healthy plants
We are beginning to understand that you can’t have healthy plants without healthy soils. Microbes play a huge role in this. They are responsible for:
Decomposing organic matter and making nutrients available for plants
Soil aggregation: by creating clumps in soil, microbes and micro-algae in particular help to prevent soil erosion
Storm water management: microbes are involved in regulating water run-off and infiltration into the soil
A healthy soil, like any ecosystem, fundamentally depends on biodiversity. When talking about microbes, this means not just bacteria, but also viruses, protozoans, micro-algae and micro-fungi, most of which are invisible to the human eye. You need a balanced ecosystem with all these different players to sustain biological equilibrium in the soil. Predator-prey dynamics, competition and cooperation applies on the microscopic scale too. For example, viruses and protozoans feed on bacteria and maintain a balance; if they were missing, bacteria would proliferate and the soil ecosystem would be damaged.
Microbes also play a complex role in keeping plants healthy:
Microbes decompose organic matter which is then absorbed by plants to enable them to grow
Fungi allow plants to communicate with each other
Microbes on the outer surface of leaves form thin biofilms that help protect plants from pathogens and from desiccation
Mycorrhizal fungi extend the surface of plant roots so that they can bring up nutrients more easily
Bacteria help the mycorrhizae become resistant to pathogens and also assist by converting nutrients into forms more easily absorbed by plants
Microbes are also involved at almost every stage of the nitrogen cycle, for example helping to fix nitrogen from plant roots into the soil (as anyone who grows peas and beans knows, this is a great way to fertilise your soil for your next crop).
We are just beginning to explore ways in which microbes might help us in the cultivation of plants. Biofilms containing beneficial bacteria are being used to improve the soil around plants, and thereby boost plant health. Microbial inoculants are used to infuse the soil with beneficial microbes which contain hormones that activate plant growth. And biopriming involves coating the seeds of plants with a bacterial solution that aids germination. These innovations are mainly used in agriculture, and could help to finally reduce reliance on pesticides and artificial fertilisers.
Our gardens can be much more than just a place to relax and look at pretty plants. They have the potential to be the ultimate biodiverse environment, a place for us to interact with our microbial old friends. Just being in a natural environment that is biodiverse means that we are constantly being coated with microbes from the air. There’s a continuous exchange, with each of us emitting a million biological particles an hour from our bodies, as well as breathing in and ingesting millions of microbes. Getting close to the soil also means we are exposing ourselves to the most biodiverse habitat on earth.
One way to maximise the benefits, according to Robinson’s research, is to increase the complexity of vegetation in our gardens and city green spaces. Think layers of planting and diversity of plant species for a maximum of biodiverse micro-organisms. It’s also important to include different layers and heights of vegetation, mimicking the vertical stratification in a forest from the ground up to the tree canopy.
‘When you increase the complexity of vegetation so it’s more like a natural habitat…then the aerobiome, the different microbes in the air, will be much more diverse compared to say a monoculture habitat or a sports field . The air around that habitat is really low in diversity”, says Robinson.
So it’s not just about spending time in natural environments, but also about making those environments as healthy and biodiverse as possible. More diverse vegetation not only means that there will be more diversity in beneficial species, but also that the abundance of harmful pathogens will be lower.
There is also the tantalising prospect that one day we may be able to plant species in our parks and gardens that impact our health in very targeted ways. This really changes how we think about plants, as objects placed mainly for their aesthetic value in gardens, and makes them partners in our health and well-being. Currently, the research is still at a very early stage, and we can only see the broad picture, but there is already some indication that planting certain species might encourage more micro-biodiversity.
Our place in the ecosystem
While we are beginning to understand the health benefits of spending time outdoors, we don’t often consider the microscopic level, the invisible life that is teeming in healthy soils, plants and air. Understanding our place in this interconnected web of life could make us much healthier and maybe even happier. Imagine, for instance, if doctors approached our health from an ecological perspective:
“We sort-of separated ourselves from nature a few hundred years ago, in the Western world particularly, and so we start thinking we’re not an organism in an ecosystem, which is strange really. The same principles apply in our body as in an ecosystem, so you can start thinking about [medical] interventions from an ecological perspective that will improve human health”, says Robinson.
Perhaps it’s time to reacquaint ourselves with our old microbial friends, and where better to start than in our gardens?
Jake Robinson’s book Invisible Friends: How Microbes Shape Our Lives and the World Around Us, will be published in March. It can be pre-ordered on his website.
Selwa Calderbank is a journalist and blogger with a focus on sustainability and environmental issues, as well as horticulture. She writes The Green Gardening Newsletter, which is available via her blog: The Nostalgic Gardener. She is also on Instagram @the_nostalgic_gardener
Selwa is being paid for this article.
Photo credit: Selwa Calderbank
Writer and editor seeking two different kinds of garden writers/researchers
I was contacted by Elisabeth Plumlee-Watson recently asking for help regarding developmental writing on a book she is working on. Sharing her request here in case anyone in this community is able to help:
US-based writer and editor Elisabeth Plumlee-Watson is doing developmental work on a how-to garden book project on container gardening and seeks people with knowledge of and lived experience of two areas:
1) Permaculture's rootedness in Aboriginal Australian agricultural and living-world knowledge: both in terms of the way Permaculture founders Bill Mollison and David Holmgren and their followers have framed their use of Aboriginal knowledge and in the way contemporary Aboriginal thinkers/workers understand/experience this framing now.
2) gardening with a disability where use of containers (pots, windowboxes, crates, etc...) has made gardening possible where it otherwise might have been impossible (or much, much harder).
Elisabeth is hoping to have one or two hour-long conversations via Zoom (or structured email exchanges if this is easier) with individuals who have lived experience and expertise in these two areas. She will pay interviewees the same hourly rate as she is being paid to work on this project if they agree to have a conversation.
If you have lived experience in either of these two areas and/ might be interested in speaking, please contact Elisabeth at firstname.lastname@example.org.
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