A woodchip mycofilter is a simple landscape feature that uses woody organic material, water movement and naturally occurring fungi and microbes to help manage runoff. On a lifestyle block or small rural property, it can be part of a planted drain, swale, shallow treatment bed or other area where water already travels.
The basic idea is straightforward: direct runoff through or across a permeable layer of woodchips. The chips slow the water, trap some suspended sediment and provide a carbon-rich habitat for decomposer fungi and other microorganisms. Plants, roots and additional filter materials can add further physical and biological treatment.
This is an adaptable property-management tool, not a piece of laboratory equipment. A successful system may look like an ordinary planted drainage area with a carefully placed woodchip bed.
Where a woodchip mycofilter may be useful
Small mycofilters are most appropriate for relatively low-risk runoff generated around a property. Possible applications include:
- Runoff from roofs, tracks, driveways or compacted ground where it carries soil and organic debris
- Overflow from gardens, orchards or planted areas
- Lightly sediment-laden water moving through a shallow drain or swale
- Runoff from parts of a lifestyle block where clean water needs slowing and spreading before it leaves the property
A mycofilter should not be treated as a drinking-water system or as a reliable way to remove every contaminant. Do not direct sewage, toilet waste, strongly contaminated effluent, fuel, solvents, pesticides, concentrated animal waste or other hazardous chemicals into a woodchip bed. Heavily polluted agricultural or industrial water requires appropriate assessment and treatment designed for that risk. If the source or contents of runoff are uncertain, identify the contamination before building a filter.
Observe the runoff before choosing a site
Spend time watching the property during and after rain. Look for the water’s natural entry and exit points, areas where it concentrates, and places where it already slows down. Note whether water arrives as a shallow sheet, a narrow flow or a sudden high-volume surge.
Also look for signs of erosion, muddy deposits, standing water and bypass channels. A useful site is one where water can be guided through the filter without creating a new erosion problem. Avoid placing the bed where it could undermine a building, saturate foundations, block an access route or threaten a slope.
Choose a location that can be reached for inspection and maintenance. It should have a safe overflow route for unusually heavy rain, rather than relying on the woodchips to contain every storm.
Position the filter in the natural flow path
The filter works best when water enters across a broad, stable area instead of rushing into one small point. A shallow spreader, level section or short swale can distribute water before it reaches the woodchips. Stones, coarse branches or a simple inlet structure may help reduce concentrated flow, provided they do not create a blockage.
Keep the bed permeable. Water should move through or across it and leave through a defined outlet or overflow. The aim is slow contact, not a permanent pond. Stagnant pools can smell, attract nuisance insects and reduce the predictable performance of the area.
Choose clean, untreated organic material
Use clean woodchips from untreated, unpainted and unpreserved wood. Avoid material that may contain paint, sealants, preservatives, glues, plastic, rubbish or unknown chemical residues. Do not use chips from timber waste when you cannot identify what the timber has been exposed to.
A mixture of chip sizes can create useful spaces for water movement while still slowing the flow. Coarser woody pieces may help maintain drainage, while smaller chips and leaf litter provide more surface area for microbial growth. Other clean organic materials, such as coarse bark or woody prunings, may be suitable when they are free of contaminants and do not compact into an impermeable layer.
Woodchips naturally favour decomposer fungi because they are made largely from woody plant material. As the chips weather, fungi and other decomposers use the available organic carbon and establish a living community on and between the pieces. Local fungi will often colonise the bed without assistance.
Inoculation is optional
Some projects choose to add a suitable fungal inoculant, but inoculation is not essential for a small property filter. Allowing local fungi and microbes to colonise naturally is usually the simplest approach. The important conditions are clean woody material, suitable moisture, air spaces and a steady supply of ordinary organic matter.
If you do use an inoculant, select material intended for the purpose and follow its handling instructions. Do not introduce unknown fungi or collect material from questionable sites. Inoculation does not turn an unsuitable location or contaminated water source into a safe treatment system.
Combine woodchips with plants and physical filtration
A mycofilter can be more useful when it is part of a sequence of simple features. For example, runoff might first pass through a shallow vegetated strip or sediment-catching area, then across a woodchip bed, and finally through a planted outlet zone.
Plants can help hold soil, slow shallow flow and provide additional root surfaces for microorganisms. Choose vegetation that is already suited to the site’s moisture, climate and maintenance requirements. Avoid planting species that are likely to become invasive or that cannot tolerate occasional wet and dry periods.
Physical features still matter. A grassed approach, coarse stone at the inlet, a shallow depression or a stable overflow can prevent the woodchips from being scoured away. The biological community supports the system, but good water-flow design protects it.
Build for inspection and maintenance
Keep the first installation small. A simple bed is easier to understand and improve than a large system built before the property’s runoff behaviour is known. Arrange the material so that the surface and inlet can be seen, and leave enough access to remove old chips with hand tools or small equipment if necessary.
Inspect the filter after significant rain and at regular intervals during wetter seasons. Check for:
- Sediment building up at the inlet or within the bed
- Erosion, exposed roots or channels cutting around the filter
- Water bypassing the woodchips
- Blocked outlets or an overflow route that is no longer stable
- Dead, damaged or overly dense vegetation
- Persistent standing water, unusual odours or signs that the bed is compacting
Remove accumulated sediment when it begins to reduce flow or bury the surface. Handle removed material according to what it may contain; do not spread visibly contaminated sediment around gardens or grazing areas. Top up the bed when the chips settle, wash away or decompose. Replace material when it has broken down into a dense, muddy layer that no longer allows water to pass through reliably.
Start small and expand carefully
Treat the first bed as a practical trial. Observe how water enters, how quickly it passes through, where sediment collects and how the plants respond. Make adjustments to the inlet, outlet or overflow before adding more material.
If the trial remains stable and is easy to maintain, similar treatment points can be added around the property. Several small filters may be more manageable than one large bed, particularly where runoff comes from separate roofs, tracks or paddocks. Each location should still have a safe overflow and a clear maintenance plan.
Used this way, a woodchip mycofilter becomes part of normal property water management: slow the water, keep soil in place, provide habitat for decomposer organisms, and inspect the system often enough to keep it working. It is a modest biological tool with useful potential for ordinary runoff, provided its limits are understood and hazardous water is kept out.