Biochar in SuDS: Water Quality and Climate Resilience

Biochar in SuDS can improve water quality, strengthen stormwater treatment and make urban drainage systems more resilient to heavy rainfall and drought. When incorporated into rain gardens, bioretention media, tree pits and green roofs, biochar can also support healthier planting and provide long-term carbon storage.

Sustainable Drainage Systems, commonly known as SuDS, are designed to capture, slow, filter and manage surface water close to where it falls. As developers, engineers and landscape professionals seek more effective and climate-resilient drainage solutions, biochar is becoming an increasingly valuable component of engineered SuDS media.

What Are Sustainable Drainage Systems?

Sustainable Drainage Systems manage surface water in a way that more closely reflects natural drainage processes.

Instead of moving rainfall immediately into conventional sewers, SuDS features can capture, slow, store, filter and infiltrate runoff near its source. This can reduce pressure on drainage infrastructure while delivering wider environmental benefits.

Common SuDS features include:

• Rain gardens
• Bioretention systems
• Swales
• Detention and retention basins
• SuDS tree pits
• Permeable paving
• Green roofs
• Constructed wetlands

According to CIRIA’s guidance on Sustainable Drainage Systems, well-designed SuDS can contribute to four important areas: water quantity, water quality, biodiversity and amenity.

The use of biochar in SuDS can help drainage features deliver several of these benefits alongside conventional runoff management.

What Is Biochar and How Is It Used in SuDS?

Biochar is a stable, carbon-rich material produced by heating biomass under controlled, low-oxygen conditions. This process is known as pyrolysis.

Unlike ordinary charcoal, biochar is produced specifically for use in soils, growing media and environmental applications.

Its structure contains an extensive network of pores and a large internal surface area. Depending on the feedstock, production process and application, these properties can help biochar:

• Retain water
• Hold nutrients within the root zone
• Improve soil structure
• Provide habitat for beneficial microorganisms
• Adsorb certain contaminants
• Store stable plant-derived carbon

In SuDS applications, biochar can be blended with soil, sand, compost and mineral aggregates to create an engineered growing or filtration medium.

Biochar should not be treated as a universal additive. The correct product, particle size and inclusion rate will depend on the hydraulic, planting and water-quality requirements of the project.

How Biochar in SuDS Improves Stormwater Treatment

Urban stormwater can collect pollutants as it travels across roads, roofs, car parks and other impermeable surfaces.

Depending on the site, runoff may contain:

• Copper, zinc, lead and other metals
• Oil and hydrocarbon residues
• Excess nitrogen and phosphorus
• Fine sediment and suspended solids
• Organic contaminants
• Road-derived pollution

One of the main functions of SuDS is to reduce the amount of this pollution reaching rivers, groundwater and conventional drainage networks.

Biochar can support this process through adsorption, filtration, ion exchange and interactions with microorganisms in the treatment media. Its porous surface provides sites where certain dissolved contaminants may be retained.

Peer-reviewed research into biochar-amended stormwater biofilters suggests that adding appropriately selected biochar to conventional media can improve the removal of some chemical and microbial pollutants.

Research into biochar in SuDS and bioretention media also shows that results vary according to:

• The type of biochar
• Feedstock and production temperature
• Particle size
• Pollutant concentration
• Water chemistry
• Contact time
• Flow rate
• Composition of the wider filter media

A biochar that performs well against one contaminant may not perform equally well against another. Where pollutant removal is a critical project objective, the proposed biochar and media blend should be tested against the expected stormwater profile.

Improved Water Retention and Hydraulic Performance

Effective SuDS must manage periods of intense rainfall while supporting vegetation during the dry weather that follows.

Biochar’s pore structure can increase the water-holding capacity of some soils and engineered growing media. Smaller pores can retain moisture, while larger spaces within a balanced media blend allow excess water to drain.

Using biochar in SuDS growing media may help to:

• Retain moisture following rainfall
• Maintain plant-available water for longer
• Support planting during dry periods
• Reduce supplementary irrigation requirements
• Improve soil porosity
• Reduce the effects of compaction
• Support water movement through the media

Independent laboratory testing of SoilFixer biochar reported a water-holding capacity of 270.7% for material below 2 mm under the specified test conditions. Performance within a finished SuDS installation will also depend on the soil, aggregate, compost, biochar inclusion rate and wider system design.

Biochar does not remove the need for appropriate hydraulic calculations. Storage volume, infiltration rate, drainage layers, underdrains, outlets and exceedance routes must still be designed around the individual site.

The complete engineered media should be tested to confirm that it delivers the required balance between water storage and drainage.

Can Biochar Help Reduce Peak Runoff?

Biochar may help retain and slow water within engineered growing media, potentially increasing residence time before water infiltrates or leaves the SuDS feature.

This can contribute to:

• Slower movement of water through the soil profile
• Temporary storage within the growing media
• Reduced immediate runoff
• Longer contact time for pollutant treatment
• More controlled drainage following rainfall

However, biochar alone does not determine the flood-management capacity of a SuDS installation.

The overall performance of a rain garden or bioretention system depends primarily on its surface area, storage depth, infiltration characteristics, drainage design, outlet controls and surrounding catchment.

Biochar should therefore be used to improve the media within a properly designed drainage system, rather than as a substitute for sufficient storage or hydraulic capacity.

How Biochar Supports SuDS Planting

Vegetation is essential to the long-term performance of vegetated SuDS.

Plant roots help maintain soil structure, encourage infiltration, take up nutrients and support biological treatment processes. Planting can also provide:

• Urban cooling
• Pollinator habitat
• Greater biodiversity
• Improved visual amenity
• More attractive public spaces
• Greater protection against erosion

Biochar can support plant establishment by improving moisture retention, nutrient-holding capacity, aeration and rooting conditions.

Its porous structure can also provide habitat for beneficial soil microorganisms. When biochar is combined with suitable soil, compost and mineral components, this can help create a more active and resilient root zone.

Biochar is not a direct replacement for fertiliser or compost. It generally performs best as one component of a balanced growing medium that provides the organic matter and nutrients required by the selected vegetation.

Biochar in SuDS for Greater Climate Resilience

Urban drainage landscapes increasingly need to tolerate two contrasting conditions: intense rainfall and prolonged dry weather.

Vegetation in rain gardens, tree pits and bioretention systems may experience temporary saturation during storms, followed by heat and drought between rainfall events.

Biochar can help bridge these extremes.

During rainfall, its pore structure can help retain and distribute moisture within the growing medium. During drier periods, some of this retained water may remain available to plant roots.

More resilient vegetation can help preserve both the appearance and performance of a SuDS installation. It may also reduce the need for irrigation, replacement planting and intensive maintenance.

Using Biochar in SuDS Rain Gardens

Rain gardens are shallow, vegetated features designed to receive runoff from nearby roofs, roads, driveways and paved areas.

Water temporarily collects within the rain garden before infiltrating into the ground, passing through engineered filtration media or entering an underdrain.

Incorporating biochar in SuDS rain gardens can create a more effective growing and filtration medium by supporting:

• Stormwater treatment
• Retention of certain dissolved pollutants
• Temporary water storage
• Nutrient management
• Root establishment
• Drought resilience
• Healthy microbial activity

Biochar may be blended throughout the engineered growing medium or incorporated into a defined filtration layer. The most suitable approach will depend on the expected pollutant load, hydraulic design, soil profile and planting scheme.

For higher-risk areas such as busy roads, industrial sites or heavily used car parks, biochar should form part of a wider treatment train. It should not be relied upon as the only pollution-control measure.

Biochar in Bioretention Systems

Bioretention systems use vegetation, engineered media and drainage components to capture, slow and treat stormwater.

Because the composition of the filter media directly affects hydraulic and water-quality performance, biochar can be included as a functional amendment.

Potential applications include:

• Residential developments
• Commercial developments
• Roadside bioretention
• Car parks
• Public-realm schemes
• Schools and community spaces
• Industrial landscapes
• Urban regeneration projects

Biochar can support the physical filtration, adsorption, plant uptake and biological processes already taking place within the system.

The inclusion rate should be determined by technical requirements rather than applying a standard percentage to every project.

Biochar for SuDS Tree Pits

Urban trees are frequently exposed to restricted rooting volumes, compacted soil, heat, drought and irregular water availability.

SuDS tree pits direct stormwater into the rooting environment while providing sufficient structure and drainage to support the tree and surrounding surfaces.

Biochar may improve the rooting environment by:

• Retaining moisture during dry periods
• Maintaining air-filled pore space
• Holding nutrients within the root zone
• Supporting beneficial soil microorganisms
• Improving resilience to compaction
• Introducing stable carbon into the soil profile

Biochar is also used in structural-soil systems such as Stockholm tree pits, where water management and long-term tree health must be considered together.

Biochar in Green Roofs

Biochar may also be incorporated into green-roof substrates where moisture retention and plant resilience are important.

Potential benefits include:

• Greater moisture availability
• Improved rooting conditions
• Retention of some nutrients
• Reduced nutrient leaching
• Better plant resilience during dry weather
• Stable carbon storage within the substrate

Green roofs have strict performance requirements relating to loading, drainage, vegetation, wind exposure and fire safety.

Any biochar used in a green-roof system should therefore be incorporated into a professionally formulated and tested substrate. It should not be added independently without assessing its effect on the complete roof build-up.

Supporting Carbon Reduction and Net-Zero Objectives

Biochar provides an environmental benefit that most conventional drainage materials cannot offer: long-term carbon storage.

Plants absorb carbon dioxide from the atmosphere as they grow. If the biomass decomposes or is burned, much of this carbon is normally returned to the atmosphere.

Pyrolysis converts part of the biomass into a more stable, carbon-rich form. When the resulting biochar is incorporated into soil or engineered growing media, that carbon can remain stored over the long term.

This means biochar in SuDS can support climate adaptation and carbon-management objectives within the same installation.

A biochar-enhanced SuDS project may contribute to:

• Stormwater management
• Climate-resilient landscaping
• Improved urban greening
• Long-term carbon storage
• Circular use of biomass
• Biodiversity objectives
• Environmental, social and governance strategies

Any formal carbon claim should be supported by appropriate product testing, lifecycle boundaries and a recognised carbon-accounting methodology.

Why Biochar Quality Matters

Not all biochar products have the same properties.

Performance can be influenced by:

• Feedstock source
• Production temperature
• Pyrolysis conditions
• Carbon content
• Surface area
• Pore structure
• Particle size
• pH
• Ash content
• Contaminant levels

Biochar intended for professional landscaping or environmental projects should be made from clean, traceable feedstock under controlled production conditions.

The European Biochar Certificate provides a recognised framework covering sustainable production, feedstock control, testing and biochar quality.

SoilFixer supplies EBC-certified wood-based biochar granules produced in the UK from sustainably sourced material.

Design Considerations for Biochar in SuDS

Successful implementation depends on selecting the correct biochar, using an appropriate application rate and confirming compatibility with the complete SuDS media.

Feedstock and production

The source material and pyrolysis conditions affect the biochar’s physical structure, stability and chemical properties.

Professional projects should use biochar with transparent feedstock records, controlled production and appropriate testing or certification.

Particle size

Particle size affects drainage, water retention, handling and mixing.

Fine particles can provide extensive surface contact but may influence hydraulic conductivity or generate dust. Coarser particles can help maintain pore space but may behave differently within the media.

The particle-size distribution should be selected for the specific application.

Application rate

There is no universal biochar application rate for SuDS.

The correct proportion will depend on:

• Existing soil properties
• Required infiltration rate
• Target water-holding capacity
• Expected pollutant profile
• Biochar characteristics
• Planting requirements
• Other media components

More biochar is not automatically better. Excessive quantities may change pH, nutrient behaviour, bulk density or hydraulic conductivity.

For larger or performance-critical projects, laboratory testing or small-scale trials should be considered before the final specification is approved.

Growing-media compatibility

Biochar must work alongside the other materials in the SuDS profile, which may include sand, topsoil, compost, aggregate and structural components.

The finished blend should be assessed for:

• Hydraulic conductivity
• Water-holding capacity
• Bulk density
• Total porosity
• Air-filled porosity
• Structural stability
• Organic-matter content
• Nutrient status
• pH
• Plant suitability

Expected pollutants

Different biochars can perform differently against metals, nutrients, hydrocarbons and organic contaminants.

Where water-quality treatment is a central project objective, testing should reflect the expected runoff and site conditions.

Long-term maintenance

Even well-designed SuDS can lose performance if they are not maintained.

Maintenance may include:

• Removing accumulated sediment
• Keeping inlets and outlets clear
• Replacing failed planting
• Managing weeds
• Preventing excessive compaction
• Checking erosion and flow paths
• Monitoring infiltration performance

Biochar can improve the growing media, but it cannot compensate for blocked inlets, damaged drainage components or poor long-term maintenance.

The Future of Biochar in Sustainable Drainage Systems

SuDS are increasingly expected to provide more than surface-water management.

Modern blue-green infrastructure is being designed to deliver cleaner water, reduced flood risk, healthier vegetation, biodiversity, urban cooling, attractive public spaces and climate resilience.

Biochar complements this multifunctional approach by offering:

• Enhanced stormwater treatment
• Improved moisture retention
• Better nutrient management
• Healthier planting
• Support for soil biology
• Long-term carbon storage
• More resilient engineered growing media

As expectations around water quality, sustainable construction and climate adaptation continue to increase, biochar is likely to play a more prominent role within SuDS specifications.

Its greatest value will be achieved when it is carefully selected, technically specified and incorporated into a properly engineered and maintained system.

Is Biochar in SuDS Right for Your Project?

Biochar can be a highly effective enhancement for Sustainable Drainage Systems when it is used correctly.

It can support stormwater treatment, retain water and nutrients, improve planting conditions and introduce stable carbon into rain gardens, bioretention systems, tree pits and green roofs.

However, performance depends on product quality, particle size, application rate and compatibility with the wider growing medium.

For developers, drainage engineers, landscape architects, local authorities and contractors, biochar in SuDS offers a practical way to combine water management, healthy planting and long-term environmental value within a single system.

Speak to SoilFixer About Biochar for SuDS

Every Sustainable Drainage System has different hydraulic, planting and water-quality requirements.

SoilFixer can support developers, engineers, landscape architects and contractors looking to incorporate high-quality wood-based biochar into:

• Rain gardens
• Bioretention media
• SuDS tree pits
• Stockholm tree pits
• Green roofs
• Engineered growing media
• Urban landscaping projects

Call 0345 055 8433, email help@soilfixer.co.uk or explore our biochar granules to discuss your project requirements. SoilFixer’s current contact details are confirmed on its official website.

Frequently Asked Questions About Biochar in SuDS

Can biochar be used in Sustainable Drainage Systems?

Yes. Biochar can be incorporated into engineered growing media used in rain gardens, bioretention systems, SuDS tree pits and some green-roof applications. The specification should reflect the project’s hydraulic, planting and water-quality requirements.

How does biochar improve SuDS water quality?

Biochar has a porous and reactive surface that can retain certain metals, nutrients, hydrocarbons and organic contaminants through processes including adsorption and ion exchange. Performance depends on the biochar, water chemistry and treatment-system design.

Is biochar suitable for rain gardens?

Biochar can be particularly useful in rain gardens because it can support stormwater treatment, moisture retention, nutrient management and plant establishment. It should be incorporated into a properly designed and tested growing-media blend.

Can biochar reduce flood risk?

Biochar may help SuDS growing media retain and slow water, but it does not determine the system’s flood-storage capacity on its own. Overall performance depends on storage volume, infiltration, drainage layers, outlets and catchment design.

Does biochar help plants survive drought?

Biochar can increase moisture retention in some growing media, allowing water to remain available to roots for longer. This may support plant establishment and resilience during dry periods.

Does biochar store carbon?

Yes. Pyrolysis converts plant-derived carbon into a more stable form. When biochar is incorporated into soil or engineered growing media, the carbon can remain stored over the long term.

What type of biochar is best for SuDS?

The best product will depend on the project. Important factors include clean and traceable feedstock, production quality, certification, pore structure, particle size, pH and compatibility with the proposed growing medium.

How much biochar should be added to SuDS soil?

There is no single inclusion rate suitable for every project. The correct amount depends on the biochar properties, media composition, hydraulic requirements, expected pollutants and planting scheme. Technical testing is recommended for larger or performance-critical installations.

Biochar for Stockholm Tree Pits: Improving Urban Tree Growth

Urban trees face some of the most difficult growing conditions. Compacted ground, limited rooting space, poor drainage, pollution and low soil oxygen can all restrict healthy tree development in towns and cities.

To overcome these challenges, landscape architects, councils, contractors and developers are increasingly using Stockholm Tree Pits as part of modern urban tree planting schemes. When combined with EBC certified biochar, these engineered systems can support stronger root development, better water management and healthier long-term tree growth.

At SoilFixer, we supply high-quality biochar solutions designed to improve soil performance in landscaping, green infrastructure and urban planting projects.

What Are Stockholm Tree Pits?

Stockholm Tree Pits are engineered urban tree planting systems originally developed in Sweden to improve tree survival in paved and heavily built-up environments.

Traditional tree pits often fail because roots are restricted to small areas of compacted, oxygen-poor soil. Stockholm systems create a more open underground structure using stone aggregate, soil and organic materials. This gives tree roots more space to grow while also improving drainage and aeration.

A well-designed Stockholm Tree Pit can help support:

• Better root development
• Improved water infiltration
• Increased soil aeration
• Stronger tree establishment
• Better stormwater management
• Longer-lasting urban planting

When biochar is added to the tree pit mix, the soil environment can become even more effective at supporting healthy growth.

Why Biochar Works in Stockholm Tree Pits

Biochar is a carbon-rich material produced through pyrolysis, where biomass is heated in a low-oxygen environment. Its highly porous structure makes it especially useful in urban soil systems, where water retention, nutrient availability and soil biology are all important.

In Stockholm Tree Pits, biochar acts like a natural sponge within the soil profile. SoilFixer typically adds around 5 to 10% biochar into Stockholm Tree Pit systems, depending on the project requirements.

This helps create a more resilient rooting environment for trees growing in challenging urban conditions.

Key Benefits of Biochar for Urban Trees

Improved Water Retention

Urban trees often experience inconsistent moisture levels. During dry periods, compacted or free-draining soils may not hold enough water around the root zone. During heavy rainfall, poor drainage can also lead to waterlogging.

Biochar helps retain moisture while still allowing excess water to move through the soil structure. This balance is particularly valuable in urban tree planting schemes, where trees need reliable access to water without becoming waterlogged.

Enhanced Nutrient Retention

Nutrients can easily leach through sandy, stony or free-draining urban soils. Biochar helps hold nutrients within the soil structure, making them more available to tree roots over time.

This can support stronger establishment, healthier root systems, improved canopy development and reduced nutrient loss.

Better Soil Biology

Healthy soil biology is essential for long-term tree health. Biochar provides habitat for beneficial microbes and fungi, helping to support nutrient cycling and root development.

Over time, this can create a more resilient underground ecosystem, giving urban trees a better chance of thriving in paved or restricted spaces.

Stronger Tree Establishment

The early establishment phase is critical for urban trees. If roots cannot access enough air, moisture and nutrients, growth can be slow and long-term survival may be affected.

By improving water retention, aeration, nutrient availability and microbial activity, biochar can help create better conditions from the start.

Why EBC Certified Biochar Matters

Not all biochar products are the same. Quality, feedstock and production standards can vary significantly between suppliers. This is especially important in urban landscaping and infrastructure projects, where poor-quality materials may affect soil health, water movement or plant performance.

The European Biochar Certificate, known as EBC, is designed to provide a recognised quality standard for sustainable biochar production and sale. The EBC states that its certification system helps guarantee sustainable biochar production, processing and sale, giving customers a reliable quality standard.

Using EBC certified biochar helps provide confidence around:

• Low contaminant levels
• Consistent product quality
• Sustainable feedstock sourcing
• Carbon stability
• Safe use in soil and landscaping applications

For councils, developers, contractors and landscape architects, certification helps reduce risk and supports better long-term project outcomes.

Biochar, SuDS and Sustainable Urban Drainage

Stockholm Tree Pits are often used as part of Sustainable Drainage Systems, also known as SuDS. These systems help manage rainfall naturally by improving infiltration, reducing runoff and supporting greener urban spaces.

Biochar can support SuDS tree pit designs by helping soils retain moisture during dry periods while improving infiltration during rainfall. This can contribute to reduced pressure on drainage infrastructure, improved urban cooling, better climate resilience and stronger long-term tree survival.

Stockholm Tree Pit specialists also highlight the importance of giving trees enough soil volume to mature and deliver long-term benefits to the local community.

Long-Term Benefits for Urban Landscapes

Trees planted in well-designed Stockholm Tree Pits can deliver decades of environmental, visual and social value. Adding biochar helps improve the quality and performance of the soil environment from day one.

Long-term benefits can include:

• Healthier tree growth
• Larger and stronger canopies
• Better drought tolerance
• Reduced maintenance pressure
• Improved soil resilience
• Enhanced carbon storage
• Better-performing green infrastructure

For urban developments seeking sustainable and future-proof planting solutions, combining Stockholm Tree Pits with EBC certified biochar is a practical and effective approach.

SoilFixer Biochar for Urban Tree Planting

At SoilFixer, we work with landscapers, contractors, developers and local authorities to improve soil health and urban planting performance.

Our biochar solutions are designed to support modern landscaping, tree planting and green infrastructure projects where soil quality, drainage and long-term resilience matter.

As towns and cities continue to invest in healthier urban environments, biochar is becoming an increasingly valuable tool for creating stronger and more sustainable planting systems.

Final Thoughts

Stockholm Tree Pits have transformed urban tree planting by creating better underground growing conditions in challenging environments. When combined with around 5 to 10% EBC certified biochar, these systems can become even more effective at supporting healthy, long-term tree growth.

From improved water retention and nutrient availability to stronger soil biology and better drainage performance, biochar offers significant benefits for urban landscaping projects across the UK.

For councils, developers, contractors and landscape professionals looking to improve urban tree performance, high-quality biochar is an important step towards greener, healthier and more resilient cities.

Spring Soil Preparation in the UK: Improve Soil Health with Biochar Compost

Why Spring Soil Preparation Matters

Below the surface, a new season is ready for action

Success in our gardens looks great, but the most important part happens below the surface. According to the Royal Horticultural Society, maintaining healthy soil through composting is essential for strong plant growth.

As temperatures begin to rise and daylight increases across the UK, plants start growing quickly. In order to support this growth, we need our soils in the right mood from the beginning!

After winter, however, soil can be compacted, out of balance and lacking some health. Preparing it early is what sets strong gardens apart.

That’s where SoilFixer’s organic, biochar composts & biochar give you a great start.

Start the Growing Season on the Right Foot

The Benefits of Early Soil Preparation

Winter conditions can leave soil quality struggling. Heavy rain can wash away nutrients, while frost can reduce airflow and structure.

Before planting begins, we need to build our soil back up to a healthy, balanced medium.

By improving soil early in the season, you:

• Create better conditions for root development
• Improve drainage and aeration
• Support consistent, healthy plant growth

Spring isn’t just about planting; it’s about preparing the ground for success. Our SF40 is a wonderful multipurpose biochar compost to create the perfect conditions for your plants to wake up from winter!

Why SF40 Biochar Compost Works

SF40 Multipurpose Compost combines sustainable, locally sourced brash and biochar a handful of horse manure from the farm, creating a more advanced and ‘alive’ soil solution than standard compost.

What Makes Our SF40 Effective:

• Organic nutrients that support natural soil biology
• Biochar that helps retain nutrients and improve soil structure long-term
• Improved moisture management in changing spring conditions
• A balanced growing environment across multiple applications
• Well-rotted horse manure from the farm (any horses which may have taken medication or wormers are removed)

Biochar acts like a sponge within the soil – holding onto nutrients and water while creating space for beneficial microbes to thrive.

What Biochar Does in Soil

Biochar improves soil structure by increasing aeration, retaining nutrients, and supporting beneficial microbial activity. It acts as a long-term soil conditioner, making it especially valuable in spring soil preparation.

Built for Unpredictable UK Spring Weather

UK spring weather can chop and change quickly – dry one week, wet the next.

How SF40 Stabilises Soil Conditions:

• Retaining moisture during warmer, drier days
• Allowing excess water to drain during heavy rainfall
• Holding nutrients in the soil for longer availability

This creates a more resilient growing environment during early plant development.

A Sustainable Way to Improve Soil Health

Choosing an organic, biochar-enriched compost means investing in long-term soil health – not just short-term results.

The Environmental Benefits of Our Biochar Compost:

• Using sustainably sourced, local biomass to make high-quality compost
• Locking carbon into the soil permanently with biochar
• Reducing the need for synthetic fertilisers

Using SoilFixer products is a forward-thinking way to gardening.

Final Thoughts: Strong Soil, Better Results

Get the soil right first and the results you’re after will come.

By improving your soil with SoilFixer compost, you:

• Build a stronger foundation for the season
• Support healthier, more resilient plant growth
• Improve results across your entire garden or project

Because when your soil is truly alive and balanced, everything else follows.

SF60 Super Compost Soil Improver: Uses, Benefits and FAQs

This article looks in detail at the SoilFixer SF60 Super Compost – what it is, how it is made, how it works and the benefits of using it.

The Development of SF60: From Innovation to Super Compost

Tony Callaghan has a long track record in composting – he invented the award-winning, patented hot bin composter (the patent and trademark are now assigned to Engineered Foam Products Ltd). Tony noticed the compost coming out of these bins was more sticky and held more water than normal compost.

This started a research project to investigate what compost is made of and if there was such a thing as a better compost, i.e. a super compost. Having looked at the science around what bacteria do with organic matter, the substances that make up colloidal humus,  Amazonian Dark Earth (ADE), biochar and a host of other things related to how bacteria and fungi really work in the soil, he formulated a theory and set about testing various “additions” and “formulations” of new types of compost.

Finally, there was that eureka moment – a compost that gave better growth results, which survives for many years and sequesters carbon so offsetting global warming gases. The new product (SF60) is 100% organic, natural, peat free and made from sustainable resources.

What Is SF60?

SF60 Super Compost is made in the UK using our propriety composting process and humification agent. The resulting product is a matrix of activated (enriched) biochar, colloidal humus, organic matter (compost) and plant macro- and micro-nutrients.

Formulated ready to use by gardeners and allotment growers who want to improve their soils and container growth mixes to the best they can be.

In our SF60 tests, we have seen an increase in plant growth and crop yield of 100% over the control soil.  (All plant growth testing is complex and it takes many test replications over a number of years before the average increase can be quoted. We believe most users will conservatively achieve +20% increase).

How does SF60 work?

The biochar/colloidal humus matrix acts as a ‘sponge’ for water and essential nutrients – storing them ready for use. The ‘sponge’ matrix supports increased levels of soil microbes. The microbes (notably mycorrhizal fungi) can access the stored nutrients.  Microbes form symbiotic relationships with plant roots and supply nutrients to the roots. This mechanism is sometimes described as ‘improved soil health leading to improved plant growth.

One of the easiest ways we have to describe SF60 is by thinking about sponges and what they do.

• Biochar granules are like hard sponges that absorb water and nutrients
• Enriched /activated biochar is a sponge filled with nutrients and water
• Colloidal humus is a soft sponge that absorbs nutrients and water (X3 more than biochar!)
• SF60 is a matrix of biochar and colloidal humus produced when we add biochar into the composting process.

Once we have ‘nutrient and water sponges’ in the soil we need to connect them to plant roots. Some of this happens when a root hair touches the humus/biochar particle.

However, it now appears symbiotic mycorrhizal fungi (AMF/EMF) are far more important as a transfer mechanism. The fungi and roots create an exchange system. Nutrients are sent to the roots in exchange for carbohydrate sugar from the plant.

Benefits of using SF60

• It holds lots of water – excellent water-holding capacity
• It keeps hold of water for a long time – excellent water retention
• It re-absorbs water very quickly after drying – excellent re-wetting ability
• Macronutrient (NKP) supply – has both fast and slow-release nutrients
• Micronutrients (Ca, Mg, etc) – contains micros nutrients in plant-available forms
• Improved nutrient supply to roots – builds and supports bacterial/fungal roots associations that increase nutrient supply to roots (e.g. mycorrhizal fungi, AMF)
• Reduces nutrient leaching – colloidal humus has high CEC reducing leachate losses on irrigation
• Improves soil aggregation leading to improved tilth and aeration (essential oxygen flow to roots and microbes)
• Results are long-lasting – colloidal humus and biochar typically survive in the soil for over 100 years (note nutrients transferred and removed via crop need replenishing)
• Positive environmental impact: colloidal humus and biochar both sequester carbon and help offset carbon dioxide and hence reduce the impact of greenhouse gases

Is SF60 different to biochars and activated biochars

Yes – very different.

Many biochar suppliers have moved away from supplying ‘raw biochar’ to selling ‘activated (charged, enriched) biochar’. Biochar ‘holds onto’ plant nutrients. If you think of biochar as a type of sponge – if you add a dry sponge, the first thing it does is suck up water and nutrients from the soil. Hence it is better to add a wet sponge full of water and nutrients.

Many seek to charge (activate) biochar by mixing it with compost, others by ‘soaking’ in liquid fertiliser. We have found neither to be fully effective.

We have looked beyond ‘mixing’. We start with soil biology and build a soil improver matrix that supports microbes. Many of these microbes work with the plant root hairs to move nutrients into the plants.  In our analogy above, we are filling the sponge pores with colloidal humus. This holds more water and nutrients and supports microbes.

We believe the most effective way is to add the biochar into the active compost heap and sell an ‘integrated mix’ of colloidal humus and biochar.

What is SF60 made from?

We combine green waste into a proprietary composting process with our humification agent made from biochar, micronized mineral powders, NPKs and some particulate organic matter.

The approximate composition of SF60 is:

Key: CH = colloidal humus, BC = biochar, TM = micronized trace minerals, NPK – nitrogen phosphorus, potassium nutrients, POM = particulate organic matter (i.e. compost). * Soil will contain mostly clay, sand and silt particles.

Is SF60 a fertiliser?

It depends on how you define and use the word! The dictionary defines ‘fertiliser’ as a chemical or natural substance added to soil to increase its fertility.  On this basis, SF60 is a fertiliser – i.e. a natural substance that contains nutrients (micro and macro NPK, Ca, etc) plus organic matter and biochar designed to improve fertility, i.e. plant growth.

However the term “fertiliser product” is defined and certified for use under EU/UK law. Currently, ‘fertiliser products’ are restricted to the chemical compositions of nitrogen, phosphorus and potassium (NPK). Typically fertiliser products have 10-30% NPKs and are usually soluble ‘fast release’ forms.

We are not allowed to call SF60 a fertiliser product, although we could (subject to testing and submission for approval) now call it an organic fertiliser under the new wider EU fertiliser definitions.

To maintain soil fertility, you either need to recycle nutrients or you need to replace nutrients taken away in vegetables and crops. Heavy cropping plots (e.g. vegetables) will deplete NPK nutrients from the soil and SF60.   Once fully depleted, you will have to replenish i.e. add nutrients back to the soil or container mix.

How is SF60 different to biochar, enriched biochar and activated biochar?

One of the easiest ways we have to describe the difference is by thinking about sponges and what they do.

• Biochar granules are like hard sponges that absorb water and nutrients
• Enriched /activate biochar is a sponge filled with nutrients and water
• Colloidal humus is a soft sponge that absorbs nutrients and water (X3 more than biochar!)
• SF60 is a matrix of biochar and colloidal humus produced when we add biochar into the composting process.

There are hundreds of types of biochar and only a few are proving beneficial as soil improvers. Further, how beneficial biochar is in soil depends on how they are used – raw, activated/charged, co-mixed with compost or co-composted (per SF60). Thousands of biochar papers have been published and we now have a ‘meta-analysis’that summarises these papers. It points to biochar + organic matter outperforming ‘biochar’.  We are proud that SoilFixer was one of the first suppliers in the world to identify that co-composting biochar with plant (green) waste using a specific formula of biochar and a specific composting method produced a mix (SF60) that improves soil fertility and plant growth way beyond adding enriched biochar to soil.

Do I need to add SF60 each year?

You can add the total amount needed in one session or top-up each season. The biochar and colloidal humus in the SF60 product remains in soil year after year. You can top-up and build towards 20% target by adding a bit more each year – this gradual improvement spreads the cost over more than one year.

Do remember – the product will help your plants access nutrients. However, if you are heavy cropping, the vegetables taken away deplete the NKP soil nutrients. Hence you will need to top up NPKs via your chosen organic feed/fertiliser. To maintain nutrients level – you have to put back what you take away.

Can I repair degraded (infertile) soil using one addition of SF60, i.e. in one step?

Yes, but the cost might be prohibitive, Adding SF60 can dramatically reduce the time taken to repair soil as you are adding a large percentage of stable biochar and colloidal humus.

Soil is degraded usually by a combination of nutrient depletion and loss of colloidal humus. The spiral gets faster as it proceeds – the loss of colloidal humus also affects water retention and soil aggregation leading to the dust bowl syndrome.

We feel it is fair to state the essential difference between fertile and infertile soil is colloidal humus and its role to glue and aggregating soil particles. As soil degrades, adding fertilisers becomes less effective – due to runoff (leaching).

Again, this is linked to the decline in colloidal humus. It can take 50 years to completely degrade soil and 50 years to repair using compost and no-till regimes. Compost decomposes but leaves very little colloidal humus, hence it can take a long time to rebuild the humus.

We believe adding SF60 can dramatically reduce the time to repair as we are adding stable biochar and colloidal humus.  We are happy to work with the experts who can prove this.

How long does SF60 last?

The scientific evidence suggests biochar and or colloidal humus can survive in soils for hundreds and in some cases thousands of years. The exact lifetime depends on many variables.  Our tests (using CO2 respiration levels), indicated at least 10 years. (It takes much more sophisticated test equipment to measure beyond 10 years!)

Notea; the SF60 product is approximately 60% biochar and colloidal humus, approximately 5-10% macro & micro nutrients and 30% organic matter. The organic matter part will decompose in 1-2 years.

Application rates – based on Area

• The recommended range is 2 to 5 Kg per square metre (Kg/m2).
• which is 10% by volume, 10 parts soil to 1 part SF60
• The minimum is 0.5 Kg/m2
• The maximum recommended is 10 Kg/m2 for SF60

More info on SF60 application rates and making the product go further can be found in our blog

In SF60, the biochar and colloidal humus fraction remain in soil year after year. You can top-up and build towards 20% target by adding a bit more each year.

How to use SF60

Dig (or hoe) into the soil to depth 5-10 cm.

Reasons why should always dig in your SF60:

• Colloidal humus has fantastic water holding capacity, retention time and re-wetting. If left to dry in the sun, it can lose the ability to hold water or take on water (rewetting). The colloidal molecules transform and beyond a certain dryness point this is irreversible – it no longer has any water-holding property.
• Colloidal humus acts as a soil aggregator – it helps the soil particles ‘stick’ together into small lumps. This increases tilth and helps water and oxygen flow. It cannot perform this task when sat on the surface of the soil – it needs digging in.
• Colloidal humus has a very high CEC value. It acts as a ‘sponge’ for soil nutrients, in other words, it holds onto the NKP nutrients and releases them to roots when needed. Your roots are deep in the soil – hence your colloidal humus needs to be in the soil near the roots.

Storage

Store in a cool dry place.  Preferably use within 3 months. When storing, avoid long hours of exposure to direct sunlight as this will dry the product. If the product becomes completely dry (i.e. friable) as it will lose some of the colloidal properties.

If the product becomes completely dry, rather than directly to the soil dry, it is better to revitalise it by adding it into your compost process and then add the revitalised compost/SF60 mix to the soil.

Why is SF60 sold damp/moist?

The product contains soil microbes, colloidal humus and water.  If the product is completely dried, the microbes die and the colloidal humus loses the colloidal property. As the product contains water, in line with the Growing Media Association guidelines, we should sell based on volume (number of litres) not weight (Kg) in the bag.

However, we are an online business and our products are delivered by courier based on very strict weight bands. So we state the weight and an approximate litre volume.

Is SF60 a type of compost?

Not really. Compost and SF60 are both soil improvers and both supply slow-release nutrients. However, compost contains ~95% partially degraded pieces of organic matter and ~5% colloidal humus. SF60 is 20% biochar, 40% colloidal humus, 7% trace minerals and NPKs and around 33% POM (i.e. compost).

Can I use SF60 as a compost activator?

Yes. It contains soil microbes, biochar and colloidal humus – all of these will activate/inoculate compost. However, you are using a fully formed soil additive.  To convert your compost into your own version of SF60, it is better to add the SoilFixer compost humification agent and raw biochar.

Is SF60 a source of trace minerals?

Yes – SF60 contains about 5% of micronized (very fine) powdered trace minerals

You mention SF60 contains colloidal humus? What is colloidal humus?

We define ‘colloidal humus’ as organic (carbon-based) colloidal molecules that absorb water, have exceptionally high CEC, WHC, retention and aggregation (stickiness) properties. Such colloids have significant benefits in soil and compost.

Fertile soil contains a tiny fraction of these vitally important organic colloids. We do not think it overstates the case to say they are fundamental to soil fertility. When these compounds are lost from soil, crop yield (productivity) declines.

Is SF60 some new miracle gardening product or compound?

It can work exceptionally well in certain situations! However, we work hard to avoid hype and sensation and focus on how and why things work. This can mean things get too technical for many readers. Rest assured: colloidal humus and biochar exist in nature. What we do is understand how nature makes them, what combination improves soil fertility and how to make them for you!

Does SF60 kill soil pathogens?

SF60 contains no man-made (artificial) chemical herbicides, pesticides or fungicides, i.e. anything added that kills pathogenic bacteria.

However, it does support healthy soil. Soils, composts and soil improver products can contain both good and bad (pathogenic) microbes. In nature, microbes compete ‘good vs bad’.  Although the exact means is not understood, biochar and colloidal humus appear to promote good soil microbes that form symbiotic relations with plant roots.

This healthy community of microbes and plant roots is stronger and out-competes (suppresses) many plant pathogenic bacteria. Plants are healthier.

Is the SF60 sterilised (pasteurised)?

Sterilised is normally taken to mean the killing of all microbes. SF60 is not sterilised. The product goes through a special type of hot composting at 60C. Pathogenic (‘bad’) bacteria are suppressed and killed-off by healthy microbes.

The product contains ‘good’ bacteria, so it is not sterile (defined as no living bacteria). It would be more correctly described as a pasteurised product – i.e. heat-treated to reduce harmful bacteria.

How much biochar (or SF60) should you add to your soil and compost?

In our Biochar and SF60 product pages, we simplify the application rate to “1 Kg/m2” (1 kilo per square metre of soil)

As we supply 10 and 20 Kg sacks,  the maths is simple: 10Kg will cover 10m2,  20 Kg 20m2

Returning guests please note this blog was revised 26th August 2021

This is a simplified approach. Depending on your needs, it might not be accurate enough. Below we discuss in more depth what affects application rates and how to jump through the various calculations to ensure you are on the right track.

What affects the application rates of biochar and SF60 super compost?

There are five areas to look at:

• Our soil health goal
• Application rate based on the area of soil (how many square metres, m2)
• Application rate based on the volume of soil (i.e. how many cubic metres, m3)
• Being cost-conscious: maximising the benefit whilst minimising the cost
• How you mix (apply) the biochar (or SF60)

Biochar application rates based on soil health

Your goal is likely to be: create the very best soil conditions. Your reference point for good soil is what high-quality loam – a dark rich crumbly soil. What defines and makes the rich loam is humus (not compost – read here for the difference).

Adding biochar (and SF60 super compost) positively affects the texture, tilth and organic matter of the soil. It also affects the microbial population.  Our advice (aligned to other suppliers) is to add 5% by volume of biochar. The 1 Kg per m2 approximates to 5% (but see the note below on soil depth!).

There are many biochar academic studies that report benefits from a wide range of application rates from as low as 1% to as high as 30%. If you had very poor soil you might need more, good soil add less.

Although there is a common understanding that organic matter (compost and biochar) are good, you CAN add too much.  When the organic matter goes above 20% other issues start to occur – it can dry out quickly, become friable and be subject to wind erosion. Alternatively, in very wet conditions, it can become airless and acidic (i.e. a peat bog).

It is very challenging for professional soil scientists and gardeners alike to easily validate what % of soil organic matter level (sometimes referred to as soil carbon)  their soil has and hence the optimum level of biochar or SF60 to add. One thing is certain – you cannot take it out! Gardeners on the whole are patient – building better soil over a number of seasons might be more appropriate.

Application rates for biochar (and SF60 super compost) based on Area

This is the easiest method. For example, apply 1 Kg of biochar per square metre of garden soil. However, it is also the least precise because it does not account for the soil depth. Referring to the excel chart below,  digging into a depth of 2.5cm, 5cm or 15cm produces a five-fold change in the % added (10%, 5%, 2% respectively).

Biochar application for maximum impact with minimum cost

The most powerful biochar and SF60 benefits involve interactions between the microbes and root hairs. It follows the best place for biochar is in the root zone. Our recommendation is to dig it when planting (eg seed drills, tree holes or when cultivating the soil. When you mix it into the soil you are improving the whole soil – where you choose to plant is not relevant as all the soil is better.

You can use the root-zone impact to stretch and make your budget go further!

If you are planting up and digging holes, it is more cost-effective to apply a thin layer in the bottom of the hole

It is more cost-effective to only mix biochar into the backfill soil

Example: planting 10 trees, 30cmx30cmx30cm (1x1x1 ft)
Each hole would be approx. 27 litres of soil taken out. At 5% that is 1.4 litres of biochar per backfill hole. 10 holes = 14 litres is approximately one 5 Kg of biochar.   If you dug the whole soil and added 5% by volume, that would probably be an area of 20m2. At 1 Kg/m2, that would be a 20 Kg bag (x4 the quantity).

Should I top-dress biochar onto my soil? (i.e. spread a top layer)

Preferably not. You get the maximum benefit when mixed in at the root zone. However, a top dressing when lightly hoed into the top few centimetres of soil will work. Worms will pull down biochar/SF60 into the soil.  Rainwater will flush the smallest particles down to the roots eventually (allow at least a season). Also in very hot summer conditions, biochar and SF60 left on the surface will dry out.  When it gets exceptionally hot and dry (above 60C, below 40% moisture, the colloidal nature of humus is lost).

Application ratios of biochar to soil based on volume calculations (litres, and cubic metres m3)

The volume of soil is the width of bed * length of bed * depth. But the depth of soil you are digging into will/can vary. For example: if you are hoeing in (or trowel planting) then usually you are looking at a maximum depth of 2.5cm (1 inch). If single digging 5-10 cm (3-6 inches) and double digging or ploughing 20-30 cm (12 inches).

Referring to the excel table below, adding 1Kg to a 1x1m square has a different volume of 25 litres, 50 litres or 150 litres based on the depths. Adding 1Kg would be 10%, 5% or just 2% depending on how deep you till it in.

Application ratios of biochar to soil based on weight calculations (Kg biochar. Kg soil)

Mixing ratios based on weight is by far the most complex method. You have to know the bulk density of your soil (which varies from 1-2 g/litre (or 1000-2000 Kg/m3). You also have to decide if you are working with dry weights or wet weights. Biochar can absorb 3-4 times its own weight in water. Soils can absorb 1-3 times weight.

Usually, this method is only used in academic studies. This makes it all the harder to translate the academic papers referring to 1% to 30% by weight back into real-life simple gardening application rates based on Kg/m2.

An example application rate of 10% biochar by weight

Take volume in m3 and multiply by bulk density in Kg/m3

• 1m X 1m X 0.2m  depth =  0.2m3 of soil, multiplied by bulk density of 1200 (kg/m3) =  240 Kgs
• 1m X 1m X 1m = 1m3 * 400 Kg/m3 of biochar = 400 Kg of biochar per bulk bag
• 10% by volume would be 24 Kg / m2 at 20 cm depth

We have an Excel spreadsheet available – please email help@soilfixer.co.uk for a copy.