Compost activators, accelerators, inoculators and humification agents - What are they, do they Work?

Compost activators (makers), accelerators, inoculators and humification agents are sold widely to help improve composting. What they are, what do they contain and how well do they work? Our article reveals all.

There are numerous compost activators and agents sold. There is no agreed product definition and the above terms seem to be used interchangeably by suppliers to mean an item 'added to improve composting'. We have provided more definitions of each term (below).

Some common trade names would include: Westland ‘Make your own compost’ (powder), J Arthur’s Garotta (powder) , Vitax Compost Maker (powder), Envil, Seaweed and Seaweed extracts (liquids and powder), Bio-tal (liquid), Neudorff (powder), Sachets of enzymes, microbes or herbs (eg QR), our own SoilFixer Compost Humification Agent (powder/granule).  (SoilFixer recognizes the above names and trademarks. Use of a trademark name does not imply any association with, or endorsement by, the trademark owner of any SoilFixer product. The views expressed on these products are those solely of the author).

There are also naturally occurring compost activators such as:

• Soft greens (comfrey, nettles, grass clippings, alfalfa, clover)
• Manures (cow, pig, chicken, horse etc)
• Urine (pee - from various sources!)

All these materials are 'soft' and 'easy' for microbes (bacteria) to digest. They have high nitrogen to carbon ratio (towards 10:1) and are hence good C/N balancers in your heap that has a lot of carbon-rich materials like straw, woody stalks or wood. You will often see urine (pee) listed as a compost activator. We are highly dubious of the real value. Urine has a tiny amount of urea, which in turn has tiny amounts of nitrogen. If you are hot composting - the addition of +99% water (which takes heat to remove it as steam) is negative. In a cold composting system, if the heap is very dry urine is OK. If the heap is damp, it compounds aeration issues. Our expertise says those seeing really positive impact probably have compost bins that were too dry and the water is improving the process. 

If you are struggling to get your heap warm/hot and do not have access to soft items like grass clippings, our advice would be to seek out the lowest cost "nitrogen" activator. Rather than opt for a branded compost maker - we would opt for a large bucket of pelleted chicken manure (ie fertiliser pellets) which £/kg is cheaper and does the same job.  

Below we explore definitions for each term and look at ingredients. (Remember the terms are often interchanged and used generically).

What Are Compost Accelerators? 

We define a compost accelerator as a product that increases the speed (rate) of decomposition. You might be able to activate your heap (see below) but the only real way to accelerate decomposition is to increase the heap temperature.

What is the best compost Accelerator?

What will make my compost break down faster?

Heat - higher termperature! The Q10 science law (named after Arrenhius) states: for every 10ºC increase in composting temperature, the speed of decay doubles. Hot composting at 60ºC is x32 times faster than cold composing at ambient 10C. Hot composting can (and does) deliver compost in 30 days.

You can use this rule to give a 'rough rule thumb': take the length of time your composting takes at ambient temperature in months (eg 36, 18, 12, six months) and convert to days (so 36, 18, 12, six days). If it takes 18 months at ambient it will take approx 18 days at 60C. The days are hot composting time, the months are cold composting times. (It' is totally possible to digest soft sugary wastes to compost within six days. A normal waste mix takes 30-60 days and we always recommend another 30 days resting/maturation just to be sure).

Tip: keep your compost warm! (see how at this page).   [If you want to know more about compost speed, please visit blogs I authored on HOTBIN composting covering the science of the Arrhenius equation, sometimes abbreviated to Q10. 

If heat (temperature) is the secret of fast composting, what benefit do all the composting makers, accelerators, activators and inoculation materials on sale really do?

Compost Activators (Compost Makers and Compost Boosters)

'To activate' is to get things going, trigger, start.  We define a compost activator as an ingredient added to your compost waste that helps start or improve waste breakdown into compost with minimal hassle (eg odour, flies, rats, etc).  

After a lot of searching for contents based on labels and material safety data sheets, it became clear the major ingredient in commercial activators is easily digestible nitrogen. 

The basic idea behind the formulation is based on the carbon/nitrogen ratio, where woody materials need more nitrogen to balance the carbon-nitrogen ratio back to 30:1. Hence bacterial activity is boosted when a readily digestible form of nitrogen is present - so far all OK.    

From personal testing, I became dubious about the benefit of adding accelerators. I looked at the science and ingredients a bit further. They all state 'concentrated, readily available'.  Ok... but if we're generous and say they are 100% concentrated nitrogen, then if you added 10g (typical scoop as recommended); that is 10g of 'NKP' bacterial food. Now look at the waste you're adding: typically you add 5-10 Kg of waste in a caddy/bucket and 25-50 Kg in a wheel barrow. This will have around 5% nitrogen on a weight basis, so each addition of green waste/food waste adds 250g of nitrogen. In other words you add x25 the quantity of nitrogen than that added from the activator packet. Is the nitrogen in the compost waste readily available? It really depends - in any soft food (kitchen waste) it is just as easy for bacteria to access (eat) as in the activators. Items like grass are high in nitrogen (c10%) and are readily decomposed - days at 60C.

Although one could dispute use of the term 'activator', the nitrogen aspect is often used to describe natural activators (grass, urine, manures, etc).  If your waste is really woody (high carbon) and you want to add "fast nitrogen" my advice is add your free lawn mower grass cuttings or other free items like manure! If you do want to add fast NPKs from a bucket (not everything is available during winter), then I would seek out the very cheapest form of NPKs (organic fertiliser). 10Kg tubs of chicken pellets or blood meal tend to half the price of small packs of "compost accelerators" ie,  £1.50/kg versus £3.00/kg.

If you're an advocate of one of the activator brands (ie they work for you), then maybe have a look at the contents label and just check you are happy this is a cost-effective way of adding the contents.

Tip: If your waste is general food and garden items and not particular woody first ensure it is well shredded, second insulate your compost bin to keep the bin contents hot (see these tips). These are much more likely causes for slow composting than lack of nitrogen. 

What Are Compost Inoculators?

We define a compost inoculator as the first microbes (bacteria/fungi) or enzyme-based substances added to waste to ‘kick start’ (inoculate) the composting mix. Based on our composting work, except in extremely rare situations, paying for inoculators is not required.  Most food and green waste decompose even when left on a flat surface  - because bacterial spores are everywhere. If you really want to 'kick start' the waste the advice is to add a handful of compost or soil into the new waste - both contain billions of bacteria that will inoculate for free. 

Do I need to Add Compost Accelerators (Activators, Inocualtors)?

Do Compost Accelerators Work?

If we agree on the definitions (see above) and agree on the contents within commercially available compost activators as per the above, then the answer is NO. There are plenty of readily available materials in the garden to do the job. Even if we were generous and agreed they gave a 10-30% increase in speed - this is wholly insignificant with the increase from hot composting - the speed doubles for every increase in 10C. So a hot composting system running at 60C is X32 times faster - no 'accelerator' can do this. 

Compost Humification Agents

This is a new term introduced by SoilFixer. During composting, compounds known as humic compounds (or humus) are formed. These compounds are the real active items in compost (read here). Typically compost contains less than 1-5% of these valuable compounds. A humification agent increases the amount of colloidal humus in your final compost typically to 15-30%.
   
Using the above definitions of activator and inoculator, the SoilFixer Compost Humification Agent (CHA) is both an activator and inoculator.  But these terms do not explain its main function - to increase the amount of colloidal humus. At this time, we are not aware of any other compost additive that does this. The fact it also helps with the other items such as odour, inoculation, etc should be seen as an added benefit.

If you want to learn more about the humification agent please visit our product information blog,  or you can buy it now in our shop - just link here.

How do I use Biochar in my composting?

In recent years, adding biochar to compost has become the recommended way to activate biochar. Biochar is not really added as an activator for compost. Biochar is mainly added as a means to 'activate' (ie charge the biochar particles with nutrients.  However, there are some studies showing wood biochar (ie charcoal granules) can aid composting aeration and hence the overall process.   You will also note that the SoilFixer humification agent contains biochar. The reasons for adding biochar relate to the protection of colloidal humus.