What is a compost accelerator?

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What is a compost accelerator?




There are boxes and bags of powders that contain a ‘magic’ ingredient with a claim that it will accelerate the composting process, but do they really? I’ve used one of these accelerators called ‘Garotta’ but I’m a little mystified about what is actually in it and, what is a compost accelerator?

A compost accelerator is apparently a culture of the specially selected bacteria needed to rot down green waste. It’s a way of introducing a large dose of the right bacteria instantly rather than wait for the natural ambient bacteria to multiply up to speed.

What else?

What happens if you don’t use any accelerator at all?

How to accelerate compost by aeration

Does urine accelerate composting?

Sulphate of ammonia, an alternative to urine

The effect that lime has on compost

The specially selected bacteria are absorbed and stored in a dry medium. This can then be sprinkled over green waste from which the bacteria will feed. When the accelerator powder becomes damp from the moisture on the surface of the green waste, the process will start. You then have the right bacteria in the right place at the right time. They will multiply very quickly, breaking down the waste as they do.

Why use a compost accelerator

If you are in a hurry to convert fresh waste into compost this may be an option. In my experience it works best when you add it to the contents of a compost tumbler. This is where thorough mixing plays a big part. You need to apply the accelerator powder to all surfaces of the waste. You need to apply it every time you add fresh waste. This will ensure that it will get to work as quickly as possible.

You can apply compost accelerator to the contents of a static compost bin as you feed fresh waste in. This can only go in as layers where it will sit and wait for the next delivery of fresh waste. There can’t be the mixing as with a tumbler but you could make some headway using an aerator probe to open the mass up and get some agitation.

The effect of this type of accelerator can’t really be described as composting in its own right. From what I have seen of it, this is part of the process that needs further attention and other ingredients to make it work.



If you add an accelerator and do nothing more, other than agitation through tumbling or aerator probing, you may be disappointed with what you see. When fresh green waste is subjected to the level of bacterial influx that happens when we use these accelerators the reaction is fast.

We think this is what we want, a fast break down of the material and you can see it working as the mixture physically falls apart. The structure changes and you will see how recognizable items of food waste turn into a porridge-like mash.

The down side to this speed of breakdown is that there is a sudden generation of acids. One of these is lactic acid. The mass of waste that has been treated is effectively pickled and, as we know pickling is about preserving. It could almost be described as silage.

So, we use an accelerator to start a fast breakdown but there is this problem with acid build up. If we leave it long enough the mass will eventually rot down but after the initial speed of breakdown we now have a delay. There is a way to counter this and maintain the speed and forward movement. The solution is quite simple. If you use any of these accelerators then you need to add hydrated lime to neutralise the acids.

See:  The effect that lime has on compost.

What happens if you don’t use any accelerator at all?

There is an argument for not using any accelerator when making compost. You have to ask, what’s the hurry? Even if you use an accelerator there is going to be a lengthy period of time before the compost will reach a finished state.

If you don’t use any accelerator at all, the fresh waste will deteriorate at a much slower rate. It will go as nature prescribes. The first thing you are likely to see is mould appearing on the waste. This will be the initial natural breakdown phase and it may last for a week or two. Then after this the mould will disappear and the microorganisms will get to work on what the mould has generated.

This process will keep going until the food source to the microorganisms has become depleted. At this point you will have finished compost.

If you don’t use any accelerator there is a much better chance that worms will move in and work their way into the mass. They will begin by feeding on the moulds that are generated in the early stages of decomposition. Then they will digest material that the microorganisms leave behind. Worms go for soft, easy to swallow materials that they can process and release as worm casts.

The biggest problem that worms would have if they were confronted with waste that has been treated with an accelerator is the acidity that’s generated. Worms can’t live in acidic material. The situation would change dramatically if hydrated lime was added. With the acid neutralised the worms can move in. They will also ingest some of the hydrated lime which will help with their digestion. The very fine particles help to grind what the ingested food.


How to accelerate compost by aeration

If you add nothing to your compost and rely completely on the forces of nature, then there is one thing that you must do to accelerate composting of green waste. Do what you can to get air into it. The best system of all, for this, is the compost tumbler. These are designed to keep turning over the mass. Every time you roll over a compost tumbler you are going to open up any lumps and allow air in.

To get the best out of a static bin, take out compost from the bottom of the bin. Only take it out if it looks like finished compost. This will leaving a space for the material above it to drop down.

This probably won’t happen straight away and you don’t want it all to drop at once. A gradual drop bit by bit will allow air to get at every piece. After a short while the contents will drop down and everything in the bin will have been aerated. This process can happen every time you take a small amount of compost from the bottom of the bin and will allow for more space at the top for fresh waste to be added.

Set up two compost bins. When one bin is full dig out the compost from this bin and move it to the other. The act of moving it will aerate the compost. Digging it over will cause the material to be’ fluffed up’ which means that there may not be room for everything moved from the first bin. This being the case, just leave the surplus in the first bin. Don’t be tempted to press down and compact the compost as you load it into the second bin as this will force the air out of it when you need to keep it in.

Whichever composting system you use it will help if you include shredded paper or cardboard in the mix. This will improve the structure of the composting mass. If you can allow air pockets to form, the compost in those parts will form more efficiently.

Does urine accelerate compost?

This will depend on what you are making compost from. Urine has a high level of urea in a very mobile liquid form. Urea contains nitrates, so, if we are using it as an ingredient on a compost heap we need to ask ourselves, does the heap need more nitrogen.

If you have a heap of lawn clippings with some shredded hedge trimmings and nothing else added from the kitchen, this will be short of nitrates in the mix. This type of material will rot down with nothing added but it will take longer because of the imbalance of being mainly carbon or ‘browns’.

So, here is a case for adding nitrates. Urine will provide a considerable amount of liquid nitrate which will work very quickly, balancing the carbon factor. For compost that is mainly grass and wood chip it would be quite acceptable to add urine regularly. This type of compost will make full use of it but be aware that that there will be a limit.

You need to monitor the progress of the heap over time. There will come a point when you won’t need to add any more urine because the conversion to compost will be complete. From this point on any addition of urine will be unnecessary and will ultimately be detrimental to the quality of the finished compost. You need to know when to stop.

The general advice is to dilute the urine with 4 water to 1 urine. This isn’t so necessary if you are putting it on compost but you definitely will need to dilute it if you are tempted to use it as a liquid fertiliser. Raw urine is tends to be very strong. If you deliver undiluted urine onto a small area then you risk killing the plant that you are trying to grow.

In the case of kitchen waste, there is already a high level of nitrates. This often needs to be balanced by ‘browns’ or paper and cardboard which provide the carbon element. So, adding urine to this will mean that you will need to add even more paper or cardboard to get the balance right.


You will soon know if there are are too many nitrates in your compost because there will be a smell. In an extreme case you will probably smell ammonia gas. There will also be an influx of flies and the compost will show general signs of stagnation.

If you see this happening in your compost, do not add urine as there are, clearly, too many nitrate compounds in the mix. Nitrates have been added to excess. Wet and heavy-looking compost will be in urgent need of ‘carbon’ in the form of shredded paper or cardboard. This will soak up some of the moisture which will improve the structure of the heap and, as it becomes incorporated into the mix, it will balance the excess of nitrates.

Sulphate of ammonia, an alternative to urine

If you don’t fancy the idea of using urine to help rot down a heap of lawn clippings or shredded hedge trimmings, then there is an alternative. You can buy sulphate of ammonia. This has all the same properties as urine but it comes as a prilled or pelleted, bagged version.

You could just scatter it over the forming compost. An ideal rate would be 4 oz (100g) per square metre. Don’t add any more until you have built up a layer of fresh waste to a depth of about 10 inches (250mm). Alternatively you could make up a solution of the same amount of sulphate of ammonia by dissolving it in 2 to 3 pints of water and, using a watering can, sprinkling it over the compost.

The effect that lime has on compost

Using hydrated lime is even more necessary when adding nitrates, whether from urine or sulphate of ammonia. Adding urine to grass or wood-chip will provide nitrates that balance the mix. This will mean that the compost will form but there will be acids generated as it does. These acids tend to slow down the process so adding hydrated lime will correct this.

For kitchen waste, where you don’t need to add nitrates at all, there is also an acid issue. Here hydrated lime is a must. Kitchen waste will generate a whole range of acids which will effectively ‘pickle’ the waste and slow down the transition to becoming compost. You will know if you haven’t been adding lime or not enough, if the compost smells and there are a lot of flies gathering around.

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 Can you put grass clippings in compost? Can I put urine in my compost bin? Smelly Compost

How do leaves decompose faster? Do worms help compost? What does lime do to compost?

What do I add to compost to help break it down? Can you compost leaves? What is carbon in a compost pile?

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