The process of making compost can take anything from a couple of weeks to several years – it all depends:
- on which composting process you use
- how much work you put into it
- what you call finished compost!
In this article, we’ll explore how long different methods of composting take, before finishing with ways to speed up the process.
What is finished compost?
To understand how long compost takes, and the sometimes misleading claims made about compost speed, you need to have an idea of what ‘finished’ compost is.
A well-constructed aerobic compost pile will go through several stages.
- The initial warming-up stage.
- The hot (thermophilic) stage.
- The cooling stage.
- The maturation phase.
(The cooling and maturation phases are sometimes lumped together.)
Some guides (and bin sellers) promise finished compost in two to three weeks, but they are typically talking about compost that is cooling down.
To achieve good quality compost, you need to leave it to mature, which allows the compost to stabilise.
A useful definition of finished compost is compost that is ready to be used.
Exactly how long that takes depends a bit on what you are using it for – compost you are using for seeds and young plants will require a lot longer than compost used for mulching beds in the autumn.
However, typically the entire process can take anywhere from 6 months to 2 years, depending on how you make it and what you are making it for.
Incidentally, finished compost does not mean that it has finished breaking down.
The compost will continue to break down in your soil for years, helping to boost soil structure and fertility in the process.
Hot composting is the fastest method of composting. To create a hot compost pile, you need to ensure that you have:
- Sufficient air
- Sufficient moisture
- A mixture of high nitrogen and high carbon organic materials
- Insulation (either through the size of the pile or through an insulating material)
If all these criteria are met, mesophilic bacteria will rapidly multiply and start to generate heat.
As the heat rises, they are replaced by heat-loving thermophilic bacteria, which make fast work of easily digestible organic material.
However, after the compost has cooled down, the compost is not yet ready to use.
It takes some months for microorganisms to further break down the tougher materials, for the compost to stabilize and for pathogen elimination.
You should leave the compost to mature for at least 6 months, and ideally longer, although as mentioned that does depend on what you are using it for!
Not all composts reach high levels of temperature. This is usually because the conditions are not ideal for the most active bacteria. This leads to a much slower compost process.
The method becomes slower again if there is insufficient oxygen, which results in anaerobic (without air) composting.
Overall, you can expect cold composting heaps to take at least a year, and up to two years, before being ready to spread.
Also see: Hot v. Cold Composting
Berkely Method: Compost In Two Weeks?
One of the fastest ways to make compost is to use the Berkeley method, which claims to make compost in 2-3 weeks.
While 2 weeks is just 14 days, most followers of the Berkeley method estimate it takes around 18 days – which is still exceedingly quick. Here’s a quick summary of the process.
- Chop up organic material into small pieces.
- Build the compost heap in 1 to 2 days.
- Ensure that the pile has a carbon: nitrogen ratio of roughly 1:30.
- Ensure the moisture level is about 50%.
- Build a pile of at least 36″ x 36″ x 36″, using bins if possible.
- The pile needs to be turned every day to reach a finished stage within two weeks (or slightly longer). Turning it every other day will add a week to the composting process. In most circumstances, nothing further is added to the compost heap during this process.
For more information, see Rapid Composting by Robert D. Raabe.
Despite its speed, there are disadvantages to this system.
Building a whole pile in one go is not realistic for the average gardener. What’s more, there’s some serious work involved in turning compost daily (or even every other day.)
Fortunately, most composters can achieve hot composting without regular turning by using bulking material to create free air space in the compost pile or bin.
As mentioned before, the final compost needs to be left to mature before using in the garden.
Also see: 13 Different Ways To Make Compost
Insulated bins such as the HotBin compost bin or the Green Johanna are great alternatives to compost piles.
HotBin estimates that rough (i.e. not ready to be used!) compost can be made in four weeks, while finer compost can be made in about three months.
Compost tumblers are designed to aerate the compost in order to speed up the decomposition process. One study by Which Magazine found that they took around ten weeks.
While that’s four weeks longer than conventional bins which were regularly forked over, the process requires less effort than turning with a fork or pitchfork.
Other Methods Of Composting
Vermicomposting refers to composting with worms.
The process is very different to standard composting! Instead of building a large heap of organic material, you feed suitable material/waste food to worms.
In a home worm composting system, it takes around 6-8 weeks for the worms to make a reasonable amount of compost, but it is usually harvested every 3-6 months.
Bokashi ‘composting’ is also very different. Small amounts of compost material are placed in a bin with microbes which are added in a powdered form.
The process takes about two-three weeks.
However, the finished results are not really compost, but a digested food material sometimes called “pre-compost”.
Learn more about Bokashi bins.
Speeding the process up
All methods of composting require patience. However, there are many ways to speed it up. These include:
I. Ensuring you use a mixture of green and brown materials to provide microbes with the energy they need.
II. Shredding or chopping compost material. This increases the surface area microbes can access.
III. Monitoring temperature levels and taking action if it is too hot or too cold. For example, if the temperature is too low, you could turn the compost to introduce more oxygen.
IV. Ensuring the compost is aerated. Here’s 11 ways to do that.
V. Adding biochar, which helps speed the process up, especially when inoculated with bacteria.
VI. Adding a hot water bottle at the start of the process to encourage thermophilic bacteria.
There are a host of other things you can do to speed up composting – see 16 easy ways to get faster compost for details.
Wrapping up: Quality v. Speed?
While there are a number of ways to get faster compost, if you want high-quality results which will really benefit your soil structure and fertility, it’s going to take some time.
It’s quite possible you’re like me when I started composting! I wanted compost fast, and spent time looking for shortcuts.
Shortcuts can backfire! I found that out when I gathered fresh municipal compost, still steaming as I bagged it, and added it to my veg patch. The results were very poor!
However, it’s worth remembering that after you have been composting for a while, and have a good system set up, it’s easy to have a steady supply of compost coming through.
If you get things right, as one compost heap gets used up another will be finishing its maturing process. And if you’ve left it long enough to mature, it will reward you by improving your soil for years to come.
Compost can not turn into soil! Compost is made up of organic matter (OM). Soil does contain organic matter, but it also consists of sand, silt and clay. Typically, the organic matter level in soil is around 10% (when measured in volume).
There are many factors that can increase the length of time compost takes. These include insufficient oxygen, too much or too little moisture, the size of the organic materials used (smaller particles break down faster) and the temperature level of the compost.
While compost doesn’t go off just because it is sitting in a pile, it does continue to break down and reduce in size. So, if you leave it too long you will have less compost to add to the soil.
Photo credit: Tiffany Woods