Life under your feet – feeding plants and the planet

RHS soil scientist Dr Marc Redmile-Gordon shares the secrets of Earth’s richest habitat

If you have access to a garden, no matter how challenging you find the soil, it is hard to overlook the great things soil can do. From heavy clays to more droughty sands, healthy soils support plant growth and ecosystem services.

These gifts are mainly bestowed by the ‘soil microbial biomass’. This scientific term describes the total of all of the living things in soil that are too small to be seen with the naked eye5. We now understand that gardeners can work with this hidden underground community to improve the benefits that any garden soil provides.

Gardening with soil microbes in mind can put us back in touch with the restorative powers of soil

- Dr Marc Redmile-Gordon

Soil as habitat
Soil is now thought to be home to about 90% of all species of fungi, and half the world’s species of bacteria, making it a key biodiversity hotspot6. This microbial life performs unique and vital work for environmental quality. It reinforces soil structure by 1) enmeshing with an underground network of thread-like fungal hyphae, and 2) bonding clay particles into place with microbial glues called ‘Extracellular Polymeric Substances’ or ‘EPS’1.

These EPS are large carbon-bearing molecules, like sticky proteins and polysaccharides, which are manufactured by the soil microbes to co-operate and modify their habitat. This gives the microbes special abilities, such as acting in co-operative clusters to store water, and keeps small capillaries open for transport of nutrients. These microbial glues also stabilise the soil’s microscopic architecture (a network of soil pores and channels) and this is central for plant growth and environmental protection, because an ‘open’ pore-network helps to prevent waterlogging and associated greenhouse gas emissions.

The amount of EPS that soil organisms produce depends firstly on the amount of carbon made available to the microbes, but also on the soil texture2, the types of plant root exudates (compounds released by roots into soil) that they have access to3, and even the presence/absence of cooperative microbial partners4.

Soil profiles from RHS Garden Wisley. Left to right: cultivated trails field soil, uncultivated new build soil, sandy soil under long term grassland, and loamy soil under orchard.

Soil as a focus for gardening with biodiversity

While most people consider soil microbes to be ‘out of reach’, gardening with them in mind can put us back in touch with the restorative powers of soil. Just as the way in which gardens are connected to one another in the landscape supports larger biodiversity, a complex, connected, and stable soil structure created by microscopic organisms is one of the defining features of a healthy soil and ecosystem.

Marc’s top tips on how to help the health of your soil and the planet
  • Cancel your subscription to green waste collection and start composting today. This prevents needless combustion of fossil fuels. It also maximises the re-use of plant carbon and nutrients in your garden, benefits wildlife and improves soil health.
  • Maximise plant cover in your garden for as much of the year as possible. Liquid carbon (food for microbes) is provided by plant roots and sustains subterranean ‘hotspots’ of microbial activity. Plants that grow well generally put more carbon into the soil, but there is some evidence that the application of fertilisers may reduce carbon storage – so see what grows best without them.
  • Make the most of your soil. Avoid digging and other disturbance if not needed, and consider soil analysis (e.g. the RHS Soil Analysis Service) to determine your soil type, pH, organic matter and nutrient status. Knowing your soil will help you optimise your selection of plants for your various objectives. In addition to drainage characteristics, soil pH and texture (the proportions of sand/silt/clay) are often the most important properties to consider.
Using a soil testing kit
  • Keep an open mind. Contrary to many gardeners’ assumptions, sandy soils are not always free draining, and clay soils can be very well drained. This is because the biologically affected soil structure (porosity etc.) is more developed and stable in healthy soils, and is often more important for drainage than your textural class (sand/silt/clay).
  • Play with microscopes. You might be surprised!

Further reading

Selected RHS soils research:
  1. Redmile-Gordon MA, Gregory A, White R & Watts C. (2020): Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land-use. Geoderma 363, 114143–114143.
  2. Olagoke FK, Bettermann A, Nguyen PTB, Redmile-Gordon M, Babin D, Smalla K, Nesme J, Sørensen SJ, Kalbitz K & Vogel C. (2022): Importance of substrate quality and clay content on microbial extracellular polymeric substances production and aggregate stability in soils. Biology and Fertility of Soils 58, 435–457. 
  3. Wang S, Redmile-Gordon M, Shahbaz M, Ge T, Zhang M, Wu Y, Liu J, Huang Q & Cai P. (2022): Microbial formation and stabilisation of soil organic carbon is regulated by carbon substrate identity and mineral composition. Geoderma 414, 115762.
  4. Wu Y, Fu C, Peacock CL, Sørensen SJ, Redmile-Gordon MA, Xiao K-Q, Gao C, Liu J, Huang Q, Li Z, Song P, Zhu Y, Zhou J & Cai P. (2023): Cooperative microbial interactions drive spatial segregation in porous environments. Nature Communications 14, 4226.

Other references:

5. Smith P, Cotrufo M, Rumpel C, Paustian K & Kuikman P. (2015): Biogeochemical cycles and biodiversity as key drivers of ecosystem services provided by soils. Soil 1(2), 665–685.

6. Anthony MA, Bender SF & Heijden MGA van der. (2023): Enumerating soil biodiversity. Proceedings of the National Academy of Sciences of the United States of America 120 33, e2304663120.

7. Benard P, Zarebanadkouki M, Brax M, Kaltenbach R, Jerjen I, Marone F, Couradeau E, Felde VJMNL, Kaestner A & Carminati A. (2019): Microhydrological niches in soils; how mucilage and EPS alter the biophysical properties of the rhizosphere and other biological hotspots. Vadose Zone Journal, 18(1), 1–10.

About the author – Dr Marc Redmile-Gordon

Marc is the RHS’ Senior Scientist for Soil and Climate Change, with responsibility for the Soil Analysis Service and the Soil Health Platform project. Marc trained at Rothamsted Research and joined the RHS in 2018, aiming to help gardeners manage flows of carbon and nitrogen to mitigate against biodiversity loss and climate change.

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