Urban green infrastructure already works through living systems. Rain gardens, bioswales, urban forests, planted drainage systems, wetlands, green corridors, parks and other soil-based stormwater features bring together water, plants, soil, microbes and organic matter. Their performance depends on how these components interact: vegetation slows and uses water, soil stores and filters it, organic matter supports biological activity, and drainage layers help move excess water safely.
Fungi are part of this picture whether or not a project is labelled “fungal.” They occur naturally in healthy soils, mulch and woody plant material. The practical opportunity is not to replace established green infrastructure with separate fungal installations, but to consider where fungal processes may complement systems cities are already building.
Fungi Already Belong to Soil and Mulch
Fungi are normal components of soil food webs. Many species grow through organic layers, where their networks help decompose fallen leaves, wood fragments and other plant residues. Decomposer fungi are particularly associated with woody materials because they can break down complex compounds in wood over time. This process contributes to the gradual transformation of mulch and plant residues into smaller organic materials that can become part of the soil.
Woody mulch therefore has two roles in a landscape. It is a practical surface material that can reduce erosion, moderate soil conditions and protect exposed soil, but it is also habitat and food for decomposer organisms, including fungi. The fungal activity that develops in mulch is usually part of ordinary ecological succession rather than evidence of a special treatment.
Mycorrhizal fungi form another important relationship with plants. In suitable conditions, these fungi associate with plant roots and exchange resources with them. The relevance of that relationship depends on the plant species, soil conditions, moisture, disturbance and broader site ecology. Mycorrhizal inoculation should not be treated as universally necessary. A well-designed planting scheme and healthy soil may already support relevant fungal relationships, while an introduced inoculum may not persist or provide a measurable benefit in every urban setting.
Where Fungal Processes May Fit
Fungal activity can be considered within the organic and soil layers of rain gardens, bioswales and planted drainage systems. Suitable, clean woody mulch or other compatible organic materials may provide habitat for decomposer fungi while supporting the wider soil community. In urban forests, parks and green corridors, retained woody residues and undisturbed soil layers may similarly contribute to biological continuity.
Any organic layer must be selected for the whole system, not added simply because it supports fungal growth. Its texture, depth, stability and decomposition rate affect water movement and maintenance needs. Materials should be arranged so that they do not seal the surface, obstruct underdrains or create prolonged anaerobic conditions. The system must continue to accept, store, filter and safely discharge stormwater under both ordinary and intense rainfall.
In this context, fungi are one biological layer among several. Physical filtration by soil and aggregate, plant uptake and root activity, microbial transformation, sediment capture and fungal decomposition may all occur together. The relative importance of each process will vary with the design, the material used, the water chemistry and the time available for treatment.
Natural Colonisation and Deliberate Mycofiltration
It is useful to distinguish passive fungal colonisation from deliberate mycofiltration. Passive colonisation occurs when fungi arrive and establish naturally in soil, mulch or woody organic matter. This is generally integrated into ordinary landscape ecology and does not require a separate fungal treatment system.
Deliberate mycofiltration is more specific. It involves designing or operating a fungal-containing medium with the intention of helping intercept or transform contaminants in a defined water flow. Such systems may be relevant to selected pollutants and particular site conditions, but their performance should not be assumed from the presence of fungi alone. Pollutant capture or transformation can depend on fungal species, substrate, temperature, moisture, contact time, pollutant concentration and the behaviour of the material as it ages.
For this reason, fungal processes should be presented as a potential contribution to filtration and transformation, not as a universal solution for urban pollution. Demonstration projects should measure outcomes rather than infer them. They may compare inflow and outflow water, track hydraulic behaviour and examine how organic media change over time. Monitoring can help determine whether a proposed fungal layer adds useful treatment without compromising the primary drainage function.
Using Local Woody Materials Carefully
Council tree prunings and other clean woody waste may offer locally available inputs for mulch or organic layers. Using such materials can connect urban vegetation management with green-infrastructure maintenance and reduce the need to transport suitable material elsewhere. However, “woody” does not automatically mean appropriate. Materials should be screened for contamination, unsuitable debris, excessive fines and other properties that could affect water quality or flow.
Designers should also consider the difference between fresh, stable and partially decomposed material. Organic matter changes as it breaks down. It can settle, become finer, consume oxygen and alter the physical structure of a filter or drainage layer. Specifications should therefore address particle size, placement, depth, replenishment and access for inspection, rather than treating mulch as a permanent component.
Hydraulics Come First
A fungal-friendly design is still a stormwater design. Hydraulic performance and overflow capacity must remain primary requirements. Rain gardens and bioswales need adequate conveyance, infiltration or underdrain capacity for their intended conditions, along with a safe path for water that exceeds that capacity.
Organic materials should not be piled where they can wash into inlets, block outlets or reduce the available storage volume. Plant selection, soil grading, erosion protection and maintenance access remain essential. Fungal activity can complement these measures, but it cannot compensate for poor grading, undersized drainage or inadequate overflow arrangements.
Maintenance and Material Management
Maintenance plans should include inspection of inlets, outlets, overflow routes, ponding duration, erosion, sediment accumulation and the condition of mulch or other organic media. Mulch replacement may be needed as material decomposes, settles or is displaced. Replacement should preserve the designed surface levels and avoid burying plant crowns or obstructing drainage features.
Spent material requires particular care where pollutants may have accumulated. It should not automatically be spread elsewhere as ordinary garden mulch. The appropriate handling route depends on the material, the site history and the contaminants present or suspected. Sampling, site-specific assessment and applicable waste-management requirements may be needed before reuse or disposal.
Start With Monitored Demonstrations
Parks, streetscapes and council facilities could provide useful settings for carefully monitored demonstrations. A project might test a fungal-friendly organic layer within an otherwise conventional rain garden, bioswale or planted drainage system. The purpose would be to evaluate practical questions: Does the material remain hydraulically stable? How often does it require replacement? Does it support useful biological activity? Are there measurable changes in selected water-quality indicators? What happens as the material ages?
Such demonstrations should include a clear baseline, defined performance measures and maintenance records. They should also be designed so that a trial component can be removed or modified without putting public safety or the wider drainage system at risk.
Fungi as a Deliberate Component, Not a Replacement System
Green infrastructure does not need to become “fungal infrastructure.” Fungi can simply become a deliberately considered biological component within systems cities are already building. Their natural role in soil, mulch and woody organic matter makes them relevant to the ecological functioning of rain gardens, bioswales, urban forests, wetlands and other planted systems.
The most credible approach is additive and evidence-led: retain established green-infrastructure design standards, protect hydraulic performance, select materials carefully, monitor emerging fungal applications and manage spent media responsibly. By working within proven water, soil and vegetation designs, fungal processes may expand what urban green infrastructure can do without asking cities to build an entirely separate category of infrastructure.