Understanding the soil microbiome
The hidden workforce behind sustainable planting
Healthy and sustainable landscapes begin below ground, yet the health of the soil itself is under significant threat. Globally, around one third of all arable land has already degraded due to erosion, compaction, salinisation, nutrient loss, and pollution. UNESCO estimates that as much as 75% of soils are degraded to some extent, and without intervention this could rise to 90% by 2050. The FAO (Food and Agriculture Organisation of the UN) warns that the equivalent of one football pitch of fertile soil is lost every five seconds, and that the world may have only a few decades of productive topsoil left.
This global soil crisis not only threatens food production, but also impacts landscape performance and long-term plant health. For landscapers, this translates into rising challenges: plants that fail to establish, soil that cannot retain moisture, increased reliance on chemical inputs, and higher maintenance costs over time. Landscapes that appear healthy at first can quickly decline if the soil lacks the biological life needed to support strong root systems and natural nutrient cycling.
The soil microbiome is central to solving this problem. This living network of bacteria, fungi, protozoa, and other microbes helps break down organic matter, unlock nutrients, build soil structure, and protect plants from disease. A functioning microbiome can dramatically improve plant resilience, reduce dependency on fertilisers and pesticides, and support more stable, low-maintenance landscapes.
Understanding and supporting the soil microbiome is not just good practice, it is a practical and necessary step toward delivering healthier, longer-lasting outdoor environments in commercial and residential projects alike.
What is the soil microbiome?
The term ‘soil microbiome’ refers to the vast and varied population of microorganisms living in the soil. These include bacteria, fungi, protozoa, nematodes, archaea, and microscopic algae. Together, they form an interconnected web of life that interacts continuously with plant roots, organic matter, water, and air. Each organism has a role to play in this underground ecosystem, contributing to a balanced environment where plants can thrive.
The soil is a collective of many different microbial lifeforms. Bacteria break down organic material and release nutrients. Fungi, including mycorrhizal fungi, form intricate networks that connect plant roots and help them absorb water and minerals. Protozoa and nematodes regulate bacterial populations and keep the system in balance. This active and adaptive community supports plant health in countless ways, many of which are only just beginning to be fully understood.
One of the most prominent relationships within the microbiome is the partnership between plant roots and mycorrhizal fungi. These fungi attach themselves to plant roots and extend their hyphae far into the soil, dramatically increasing the plant’s reach for water and nutrients. In return, the plant provides the fungi with carbohydrates produced through photosynthesis. This mutual exchange boosts plant growth, especially in poor or compacted soils, and can reduce the need for fertilisers.
Why it matters
In landscaping, success is often measured by how well plants establish, grow, and perform over time. The soil microbiome is one of the most important, yet often overlooked, contributors to this success. When the microbiome is healthy and active, it improves the soil’s ability to support plant life naturally.
A thriving microbial ecosystem helps plants build stronger, deeper root systems, which improves stability and drought tolerance. Nutrients are made more available through microbial activity, allowing plants to take in what they need without relying heavily on synthetic fertilisers. Microorganisms also create natural disease resistance by outcompeting harmful pathogens and stimulating plant immune responses. This means fewer issues with pests and diseases and less need for chemical interventions.
Good soil structure is another benefit. As microbes move through the soil, they bind particles together to create aggregates. This improves soil aeration and drainage, making it easier for roots to grow and water to penetrate. These natural processes all contribute to healthier, more robust plantings.
In large-scale commercial landscapes, where consistency and reliability are critical, the role of the soil microbiome becomes even more significant. It lays the foundation for sustainable, low-maintenance landscapes that can perform well for years without excessive input or replanting.
Challenges in modern landscaping
On a modern, bustling construction project, it’s very easy for the value of good quality soil to be overlooked by the immediate requirements of project. As such, the soil microbiome is often disrupted or even destroyed during the typical construction or landscaping process. On construction sites, topsoil may be stripped away or compacted by heavy machinery. Subsoil, which is low in organic matter and microbial activity, is sometimes left behind or used as fill. These disturbed soils are poor environments for microbial life and do not support plant health well.
Chemical fertilisers and pesticides, while offering short-term solutions, can also damage soil biology. High levels of synthetic nitrogen, for example, can reduce the diversity of microbial populations. Pesticides may eliminate both harmful and beneficial organisms, weakening the natural balance of the soil ecosystem.
The industry is also often under pressure to deliver fast results. Landscapers may be asked to achieve immediate visual impact, which can lead to the use of pre-grown plants, instant turf, or nutrient-boosting products that prioritise appearance over long-term sustainability. Unfortunately, these quick fixes may overlook the importance of healthy soil and microbial support, leading to plant failure months or years down the line.
For example, on a housing development, to meet tight deadlines, contractors may be encouraged to lay instant turf over compacted subsoil, install mature hedging for quick structure, and apply high-nitrogen fertilisers to boost short-term growth. While these measures can create an attractive landscape in the short term, problems often arise within a few months. Without proper soil preparation, turf may struggle to root into dense, biologically inactive ground, leading to patchy, uneven growth. Hedges can show signs of stress, such as leaf drop or dieback, as they fail to establish strong root systems. In the absence of a healthy soil microbiome, plants may become more reliant on irrigation and pest control, and the space may require costly maintenance or replanting.
Prioritising appearance over long-term resilience can lead to worse results down the line. When soil health is overlooked, landscapes can falter despite the best planting efforts. Whereas preserving topsoil, improving organic content, and introducing microbial support such as mycorrhizal inoculants can set up even fast-paced projects for long-term success.
Understanding these challenges is the first step toward addressing them. The good news is that with a more informed approach, many of these issues can be overcome.
What can contractors, architects and specifiers do?
Much of the responsibility for soil health lies with those designing and managing landscaping projects. The decisions made at the planning and construction stages can have a lasting impact on the microbiome and, by extension, on the overall success of the landscape.
One of the most effective steps is to preserve existing topsoil whenever possible. This involves several important practices. Protecting the soil from compaction is critical, which can be achieved by limiting vehicle access, using designated pathways, and installing temporary ground protection mats during construction. Avoiding unnecessary removal of topsoil means planning works so that soil disturbance is kept to a minimum, and when excavation is required, storing topsoil separately and carefully for later reapplication.
Keeping topsoil covered is also essential. This could involve using mulch, cover crops, or geotextiles to protect it from erosion, desiccation, and temperature extremes. These coverings help retain moisture and support microbial activity during site preparation and delays.
Where new soil must be imported, it is important to specify high-quality topsoil or blended soils with adequate organic matter, stable structure, and evidence of biological activity. This might include sourcing soil that has been compost-enriched, contains biochar, or is inoculated with beneficial microbes. Verifying the source and composition of new soils through supplier data or independent testing can help ensure they will support a healthy and active soil microbiome.
Selecting plants that are compatible with the site’s natural conditions can also help. Native and well-adapted species are more likely to form strong relationships with local microbes, supporting a balanced ecosystem. For example, on heavy clay soils that retain moisture and are slow to drain, Cornus sanguinea (commonly known as Dogwood) is a UK native shrub that establishes well. It tolerates waterlogged conditions, supports beneficial fungi and insect life, and adds seasonal interest with its stems and flowers. Including a diverse mix of suitable plants can further enrich microbial diversity, reduce vulnerability to pests and diseases, and create a more resilient planting scheme.
Another valuable action is soil testing. Simple soil assessments can reveal important information about structure, organic matter, and biological activity. For example, a test might show that the soil has low organic matter and poor microbial activity, but adequate levels of phosphorus and potassium. This would suggest the need for organic amendments, such as compost or well-rotted manure, rather than additional fertilisers. It might also indicate that introducing mycorrhizal fungi or other microbial inoculants could help boost soil life and improve nutrient cycling. These insights allow for more tailored soil preparation and informed decisions about fertiliser use, planting strategies, and long-term maintenance.
If you would like more information on preparing sites to prioritise soil health, you can read our blog here.
Cornus sanguinea ‘Midwinter Fire’
The soil crisis: A global challenge
The importance of the soil microbiome cannot be overstated, yet the health of our soils is under serious threat. Globally, we are facing a soil crisis driven by urban expansion, industrial agriculture, deforestation, and pollution. According to the Food and Agriculture Organisation of the United Nations, one-third of the world’s soils are already degraded, and losing fertile topsoil at an alarming rate.
This degradation is closely linked to a decline in soil biodiversity. As natural soils are replaced or treated with heavy inputs of fertilisers and pesticides, microbial life declines. This disrupts nutrient cycles, reduces water retention, and weakens natural defences against disease. As a result, soils become less productive, less resilient, and more dependent on external inputs.
For the landscaping and horticultural industries, this is a major concern. Poor soils mean struggling plants, higher maintenance costs, and less sustainable outcomes. Restoring microbial health is a key part of reversing this trend and building a more regenerative approach to green infrastructure.
The soil microbiome holds the key to natural plant health, strong root systems, and long-term sustainability of horticulture and agriculture on Earth. As our industry shifts toward greener practices, understanding and protecting this underground ecosystem is no longer optional, it is a necessity.
At Greenwood Plants, we are committed to being part of the solution. By nurturing soil biology from the earliest stages of plant growth, we help landscapers and architects build more resilient green spaces. Our focus is not just on supplying quality plants, but on supporting the living systems that make those plants thrive.