SUSTAINABILITY  |  Read Our Commitment

Compost Activators & Compost Humification Agent Q&A

Tony Callaghan 25/10/2016

Compost Activators & Compost Humification Agent Q&A

This blog provides detailed information on SoilFixer's Compost Humification Agent. The first page covers the highlights per the website product specification page. If you have already read the website product page, please jump down to start at the question 'what is the story around the product development'.

What is the Compost Humification Agent (also known as a Compost Activator)

It is a granular powder sprinkled onto new waste added to the compost heap or bin. The powder promotes and boosts the formation of the highly beneficial 'colloidal humus' portion of the compost from typical levels of under 5% to 10-40%. This patent-pending NEW product is unlike any existing compost activator (accelerator or inoculation agent). Developed by Tony Callaghan (inventor of the hot bin composting system UK patent 2496234) following years of work on compost and how to make more of the really good stuff that improves plant growth.

Benefits of using the SoilFixer Humification Agent in your compost

  • Compost made with the humification agent boost plant growth - in our tests by up to 100% increase in growth and crop yield * (see note)
  • Your compost will look and feel smoother and stickier – it will have more of the vital colloidal humus
  • You will be making a positive, long-term improvement in your soil. Colloidal humus and biochar are long-lasting and even small amounts have profound impacts on soil fertility
  • You will be making a groundbreaking contribution to the environment. Colloidal humus and biochar are stable forms of organic carbon known to survive in soils for hundreds of years. You will be sequestrating carbon and offsetting the impact of global warming gases like carbon dioxide

Be amazed at how much better compost can be!

(* Note: in our tests we have seen increases in growth and crop yield of up to 100% (double!). All plant growth tests are challenging due to the number of variables. The results need further validation. The only way to completely test this product is via users. We are confident your improved “compost” will deliver at least a 20% increase in yield).

Who should buy the compost humification agent?

  • All composters who want to improve the quality (performance) of their compost
  • Home composters using traditional garden (green waste) 'cold' composting in darlex and pallet frame boxes
  • Hot composting systems such as HOTBIN®, Ridan® and Rocket ® (SoilFixer recognises the owners of these trademarks. Use of the trademark does not and should not be taken to imply any endorsement of SoilFixer products by the trademark owner)
  • Industrial composting sites using windrows or IVC system

How do I use the Compost Humification Agent?

Each time you add new waste to the compost bin, sprinkle on the agent and rake it in. Add 100g (one mugful or a handful) per each 5Kg (approx. 7-9 litres, i.e. a large caddy/bucket) of waste.

(Note: If you are hot composting and using wood chip as a bulking agent, consider replacing your wood chip with biochar granules (0-8mm). Biochar is a great bulking agent and soil improver. You will be on a path to make a DIY version of SF60 – our super compost / super soil improver.


A black/grey granular powder, 100% passes through a 20 mesh sieve (2mm) sieve.
Available in 5, 16-litre tubs. Sold based on volume (litres). The bulk density varies 0.5-0.6 g/l, hence tubs weigh in the range of 2.5-3.5 Kg or 8-10 Kg.

What is it made from?

It is a proprietary formula developed by SoilFixer. The formula contains biochar and micronized powders. The materials are all from sustainable, natural, UK sources and are 100% organic.

Does it have a shelf life?

When kept dry there is no shelf life as the ingredients do not deteriorate in air or soil.

How Do I store it?

In the tub outside, but you do need to keep the lid on to prevent rain seeping in. If the powder gets wet, it will form a paste and no longer sprinkle and mix when added. (Note if your powder has become wet, dry in the sun or indoors. If the surface 'cakes' after drying - break it up via rubbing in gloved hands or using a trowel.)

The granular powder delivers so much more than compost "accelerators", "catalysts", “inoculators” and "activators". Read more on compost activators at our composting FAQ/blog. Sprinkle the product on to your compost waste each time you add new waste to your compost heap / bin. It promotes and boosts the formation of the highly beneficial ‘colloidal humus’ from typical levels of 1-5% to 10-40%.

Why should I add SoilFixer Compost Humification Agent to my compost?

The humification agent improves your compost (and hence soil and plant growth) by increasing the amount of vital ‘colloidal humus’ in your compost. (We review what colloidal humus is below).

Our tests indicate:

  • Typical homemade and shop-bought compost has 1-5% colloidal humus.
  • Compost made using the SoilFixer Compost Humification Agent has ~40% colloidal humus (dry weight basis)

What is the story around the Compost Humification Agent product development? (How was it invented, or discovered)?

Over the past 5 years, Tony Callaghan has experimented with numerous “compost additives”, “compost bins” and “composting methods”. The search to find a truly fast and effective composting method resulted in the invention of the award-winning, patented hot bin composting system. (Note: the patent and trademark are now assigned to DS Smith plc). From the very first batches of compost made in our hot composting bins, it was noted there was a difference in both the ‘look’ and ‘feel’ of the compost when compared to compost from garden centres. This started a project to understand why and if it was possible to make such a thing as the “world’s best compost”. After reading hundreds of scientific papers and testing various compounds, we are confident that our Compost Humification Agent results in the formation of more beneficial ‘colloidal humus’. We have developed a hypothesis for why it is formed, why it exists and how it survives to benefit soil over the long term. This information has to undergo scientific peer review. We have also submitted patent applications. In the meantime, we know, no matter what the theory, only real testing by large numbers of users will provide the evidence that it works. Hence we are launching the product so more users can provide feedback.

Along our journey, there was a bit of Eureka moment when we realised we were no longer looking at a ‘better compost’, or making activated (enriched) biochar, it was about a completely new class of soil improver – based on an integrated mix of colloidal humus, biochar, nutrients and small amounts of particulate organic matter (i.e. compost). We gave this new soil improver the code name of SF60 and have been tweaking the formulation and process to make it to ensure consistent results (see our testing results). We aim to have the first batches of this 'Super Compost', 'Super Soil Improver' ready for March 2017.

How does colloidal humus differ to compost?

We have more detail in our colloidal humus blog, briefly:

Compost can be looked at as a mixture of two components, particulate organic matter (POM) and colloidal humus (CH). POM typically accounts for 95% of the total compost mixture. POM is simply small pieces of partially degraded bits of waste. This POM material has a set of properties - for example, water holding capacity, aggregation and nutrient release.

We are routinely told to add compost (organic matter) to improve soil tilth and help with water retention! Hence it will probably go against most gardeners first instincts, to note that when you compare POM to other soil components, it has relatively poor water retention and soil aggregation properties. The beneficial properties sought come from the tiny 5% fraction of colloidal humus within the compost!

Try this test: take a handful of compost roll in your palm to form a ball. Do the same with your soil. Leave both in the sun to dry for a few hours. The compost ball will quickly dry into a friable pile of bits that will blow away in the wind. Soil (and especially clay soil) will hold water more effectively - it might take two days to dry out. If you have ever added masses of compost to a raised bed – you might have noticed that in late summer, you were constantly watering it. (This is the same effect you see in a hanging basket using compost – compost actually dries out fast and is a poor material to improve water retention or soil aggregation. (More detail can be found in the table below).

The next item to review is how long the POM (i.e. 95% of the compost mixture) lasts in the soil. It usually decays (biodegrades, composts down) over 1-2 years. It does leave behind small (and vital) amounts of nutrients in the soil, but everything else reverts to carbon dioxide and water.

If we now look in more detail at the properties of the small amounts (typically >5%) of substances we collectively call colloidal humus then we find a substance with a very high water holding capacity, huge CEC value and a material that acts as the soil 'glue' that creates aggregation and tilth. The colloidal humus fraction is the highly valuable bit of compost that your soil really needs. We do not feel it overstates the case to refer to colloidal humus as the critical component in soil representing the difference between fertile and non-fertile soils.

Here is a table of soil component properties to illustrate further (note the figures are illustrative – they vary by soil type etc)



Humus (colloidal)




Water holding capacity






(WHC as multiple of own weight)

Water retention time

2 hours

24-48 hours

2 hours

24-48 hours

<2 hours

How long does it take to dry – resistance to water loss, typically measures at 20-40C.







Ability to glue soil particles into crumb – this effects aeration, water retention and hence root growth.

Aeration (pores)






Ability to help create pores and channels for oxygen flow (aeration) - effects root growth

Plant nutrients

Yes, 4%, slow





Is the component a source of plant nutrients (e.g. NPKs)

Cation Exchange Capacity (CEC)






CEC is a technical term, but in simple terms the higher the number the better it is at absorbing and holding onto nutrients.

Note Biochar means raw biochar – properties change after being in soil for many months – can you work out why that might be the case

Does the SoilFixer Compost Humification Agent work in both hot and cold composting systems?

yes. Temperature affects how fast the waste breaks down (speed of biological reaction), not whether the waste is converted to colloidal humus (the type of biological reaction).

Is it approved for organic gardens and farms?

We have not yet registered the product with any specific organic certification body (e.g. Soil Association). We can state that all the components within the product are from natural occurring sustainable and organic substances. Individually, each component used in the agent can be found on various approved lists for use in organic gardens and farms. There should be no major barrier to accreditation in due course.

What is pH of SoilFixer Compost Humification Agent?

Product pH is: 9.0 -10.5, it is mildly alkaline. (Note used as described, this will not make your final compost alkaline - mature compost prepared using the agent has a pH range 7-8).

Does the SoilFixer Compost Humification Agent contain Biochar?

Yes. It contains a significant amount of a specific size and grade of biochar. We manufacture our own biochar here in the UK.

Is it better to mix biochar with compost rather than adding biochar direct to the soil?

The agent powder contains biochar. Biochar can also be added directly to the soil, so should we add biochar to compost or the soil? From our tests, we believe it is definitely better to but biochar through a composting process rather than just mix biochar with compost and or soil.

Can I make my own humification powder?

No. The specific formula is a trade secret. For commercial composters wishing to make their own 'super compost' 'super soil improver' should contact us to discuss franchise and licencing agreements.

How has SoilFixer Humification Agent been tested and proven?

Yes, it has been tested by the SoilFixer team. We will commission independent trials as soon as we are able.

How can I test my compost to see if the SoilFixer Compost Humification Agent has worked?

There is no laboratory test to indicate you have colloidal humus in your compost. Below are some steps you can take to check you are on the right track.

Evidence Testing

Look Your compost will be much darker in colour. It should be dark brown to black and retain this colour when dried in the sun. (Compost dries quickly to light brown colour)


Your compost should be a fine texture and very wet and sticky. It should hold onto the water and resist drying. Balls of ordinary compost will dry out into friable piles with hours. Colloidal humus balls will still be drying 48 hours later.

(Note clay has the same water retention and resistance to drying as colloidal humus. You can only use this test if you have not added large amounts of soil or clay to the compost bin.


Your plants and vegetables will grow bigger and better.

Remember there are a huge number of variables that can affect plant growth. ‘Blind’, unbiased, plant growth tests are notoriously hard to undertake. You can follow our growth tests at our blog site.

Before undertaking testing, be sure to read our article on compost FAQ on compost versus blended growing media. Pure compost is not a great growth medium – you still need to blend it to create a growing mix!

Standard laboratory testing exists for: CEC, WHC, LOI – for organic matter content, Rewetting, MRT (stability) – e.g. Solvita CO2 tests, Nutrients (NKP, etc) – EC method. These tend to require a lot of time, effort and cost to carry out - they are normally outside the scope of most gardeners

Is SoilFixer Compost Humification Agent a Compost Accelerator?

We can find no agreed industry definition for what a compost accelerator is. We define a compost accelerator as a product that increases the speed of decomposition of organic waste. The SoilFixer Compost Humification Agent does not give or make composting significantly faster - so no it is not an accelerator. Using our definition neither do any of the other 'compost accelerators' actually accelerate compost!

In our opinion, the only effective compost accelerator is heat. If you want to know more about compost speed, please visit our earlier composting FAQs where we explain the impact of the Arrhenius equation (Q10 = 2), i.e. the speed at which compost breaks down doubles with every 10C increase in temperature. Roughly, if your compost takes 24 months to degrade at 10C (UK average) then it would take just 24 days at 60C.

Is SoilFixer Humification Agent a compost Activator?

There is no industry definition for what a compost activator is. We define a compost activator as an ingredient added to waste that help decompose waste into compost with minimal hassle (e.g. odour, flies, rats, etc). Using this definition, SoilFixer Compost Humification Agent is a compost activator.

Is SoilFixer Humification Agent a Compost Inoculator?

There is no industry definition for what a compost inoculator is. We define a compost inoculator as a microbe (bacteria / fungi) or enzyme based substance added to waste to ‘kick start’ (inoculate) the composting mix with bacteria.

The SoilFixer Compost Humification Agent does contain some composting microbes. Hence it can help inoculate the compost waste. But, as many good expert composting sites will tell you, a handful of soil or compost has billions of bacteria in. Soil and compost can and are used to inoculate compost heaps. Inoculating with commercial products (in our view) is rarely needed or beneficial.

How does our compost agent compare to other accelerators, activators and inoculations?

There are numerous compost activators agents, just a short list would include:

  • Westland ‘Make your own compost’
  • J Arthur’s Garotta (Powder or liquid)
  • Vitax
  • Seaweed and Seaweed extracts
  • Hydra (Biocompost)
  • Neudorff

(SoilFixer recognises above names are trademarks. Use of a trademark name should be taken to imply any association with or endorsement by the trademark owner of a SoilFixer product. The views expressed on these products are the personal views of the blog author).

After a lot of searching for ingredients, I concluded most of the available compost activators are a mix of NPK nutrients or nutrients mixed microbe cultures.

They purport to be ‘concentrated’. Well yes, but that still leaves me dubious about the benefit. When compared to on a weight basis – each addition of the activators adds a tiny amount of food (NKP nutrients) for bacteria (typically you are adding 10-100g/use, so the absolute max is 10-100g of nutrients). This is very small when you consider the weight of compost can be many kilograms. I am not alone in viewing the addition of ‘accelerator’ nutrients into the compost as being of little benefit.

So most of the commercially available activators, accelerators and inoculants are food or food plus bacteria. The SoilFixer agent is a mixture of non-biodegradable biochar and micronised powders. From our work and testing, we assert the agent affects the biological reactions that take place during composting and specifically how much colloidal humus is made.

The terms compost activator, accelerator, inoculator do not explain the benefit or the process the SoilFixer agent undertakes. We prefer the term ‘humification agent’ as it more accurately describes what it does – it aides the process of forming colloidal humus. We are not aware of any other compost additive that does this. The fact the agent also helps with the other items such as odour reduction, inoculation, etc should be seen as an added benefit.

Does SoilFixer Humification Agent help stabilise (prevent decay) of the compost?

Colloidal humus is stable, compost is not. Your compost will have more colloidal humus so as a matrix average it will be more stable. But the particulate matter (compost) will still decay over 1-2 years.

Our tests indicate the colloidal humus fraction of the improved compost is stable. As measured as a mean residence time (MRT) it was hundreds of years. The particulate organic matter in the compost is unstable and decomposes in a 1-3 year timeframe.

Does colloidal humus sequester carbon?

Yes in two ways. (1) The Humification Agent contains biochar (amongst other things) which does not biodegrade and is estimated to survive 100-1000 years. It therefore sequesters carbon. (2) The colloidal humus part of compost also has a high MRT (measured in 100 years) and this part is also termed sequestration of carbon.

Can I add both Biochar and the Humification Agent into my compost waste?

Yes. The biochar will become activated (enriched, soaked, inoculated). Activate biochar helps make a fantastic soil improver. The combination of biochar, colloidal humus and particulate organic matter (compost) is the basis for our super soil improver SF60 – see SF60 FAQ.

Using the product - health and safety

The granular powder is classed as non-hazardous. The mix contains granules of biochar mixed with very fine (micronized powders). The mixture is supplied damp. If the mixture is allowed to dry out, it will become ‘dusty’. A dust mask is advisable if these circumstances. The situation can be resolved by lightly spraying the top of the product with water from a plant mister.