How long does it take to make compost?

It can take anything from a month to a couple of years to turn your waste into compost. It depends on the types and quantities of materials used, the temperature, moisture and amount of air in the mix.

Fast compost is Hot compost.

If you want to make compost really quickly, you need to put in a lot of effort and you need a large amount of material to start with. Hot composting needs more than a cubic meter of material before it becomes viable (the more the better in fact) and works best in a cubic wooden container or open heap.

If you make a large compost heap or bin as described on our 'how to make compost' page, all at once, it will start to heat up very quickly. Within a few days it will reach high temperatures (upto 70 celcius), but pretty soon afterwards it will start to cool down.

This is when the effort is required. You need to mix the compost well by turning it over. This adds a fresh supply of air to the system to boost the rotting process. You might need to add some water too. This process needs to be repeated a few times to ensure all the material decays quickly. It will take between one and two months to produce compost this way.

The resulting compost is a light, brown, earthy substance. It will still have unrotted brown material in it (small sticks and plant stems) so you might need to sieve it before use.

The advantages of hot composting are a quick production of compost and, because of the high temperatures reached in the heap, partial sterilisation of the compost (note that although the heat kills of most weed seeds and plant diseases, it doesn't kill them all off).

Most large scale commercial composting is carried out this way.

Slow compost is Cool compost

If all that sounds like too much hard work, or you simply don't have enough material to do a 'hot rot', there is another way. Cool composting takes a little longer to produce results and is ideal for the small scale gardener using a compost bin. You make the mix in the same way, with layers, a good green/brown mix, moisture and air, but you can add the layers slowly as material becomes available.

The material will still heat up, but usually to about 30 celcius or so. This isn't hot enough to kill off as many weed seeds or diseased plants, so be careful of what you put into it.

One advantage of cool composting is that the lower temperatures mean more worms can survive in the material, which in turn means you will get a finer end product. It might take six months to a year to get good results this way.

You can always attempt to speed the process up if you get lots of good material at once - simply mix it with the existing material to get it aerated. Water it if needed then sit back and watch!

Additives to make better compost

You can add commercially available compost 'activators to speed up compost production. These are usually mixtures of naturally occurring microorganisms that speed up the decomposition process.

You can also add your own activators. A couple of handfulls of soil now and then will supply your heap with extra microorganisms. Horse manure is a great activator as it contains a wide range of beneficial microorganisms. You can also add some well rotted compost from another heap to kickstart a new heap.

Some compost experts recommend the addition of composting worms (these are 'brandling' or 'tiger worms', not common earth worms) which can be bought in some fishing shops, at garden centres, over the internet or dug up from another heap. Be careful if you are adding worms - they will not be happy in a hot heap!

The effect of seasons

Composting slows down over the winter. The lower temperatures cause the mircoorganisms to slow down, and chemical reations slow down as well. Additional winter rain can also saturate a compost heap, so try to keep a heap covered over during the winter

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