Making cold compost step by step (part 3 of 3)

Part one – low tech, low input means of dealing with green waste.
Part two – making a hot compost mix.

1) In an earlier Classroom, we looked at making hot compost where heat helps the breakdown. Cold compost, where the work is done by worms, is by far the most common form of home compost. You don’t need special facilities – a pile on the ground, compost bins or a netting ring are all fine. It needs to sit on dirt so the worms can move in. You are aiming to build up about a cubic metre of composting material at a time.

2) The ingredients and ratios are the same as for hot compost but because cold compost is not usually turned, it is better to build it in layers. Nitrogen comes from green waste (fresh leaves, vegetable scraps, lawn clippings etc) and this can be up to 60% of your mix. Carbon comes from dried leaves and stalky vegetation along with all the twiggy bits and this should comprise 40 to 50% of the mix. The carbon also traps air in the mixture and stops it turning to a sludgy mess.

3) Do not put in seed heads or diseased foliage or plants. Without heat, the seeds and diseases will survive and when you spread your compost, you will be spreading them throughout the garden.

4) The usual advice is that citrus peel and egg shells should not be added but we ignore that because we have large quantities of citrus peel to dispose of. The worms ignore it and it rots down of its own accord. However it pays not to add meat which will attract dogs, cats and rats. If you are adding newspaper, scrunch it up first or it comes out at the end of the process pretty much as it went in. Newspaper counts as carbon content.

5) The compost worms will arrive of their own accord. Striped tiger worms are the most common. If you are worried, you can buy them or transfer them from a worm farm but it is not necessary. If your compost pile gets sludgy and smelly, you do not have enough carbon content and it may have insufficient air (oxygen).

6) When you have about a cubic metre of layered mix, cover the heap or bin. Some people use old woollen carpet. Other options are heavy duty plastic, boards or corrugated iron. We use old weedmat weighed down so it does not blow off. With cold compost, it will take at least six months before it is ready to use and it may take longer over the colder months of the year. But at the end of that, you should have a clean mix which is easy to handle and nutritious in the garden. It is usually best to work with a row of compost heaps, or at least three – one you are building, one that is maturing and one that is being used.