SUSTAINABILITY  |  Read Our Commitment

SF60 Super Compost / Soil Improver Detailed Product Q&A

Tony Callaghan 20/10/2016

SF60 Super Compost / Soil Improver Detailed Product Q&A

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.

How did we develop SF60 - A brief history

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:

SF60 40% 20% 2%+5% 33%
Compost <5% 0% <2% >93%
Clay Soil* <2% 0% <2% <2%
Loam Soil* 3-4% 0% <2%


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!)

Note 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 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.


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.