Composting: introduction

“I’m a chef, I’m a cook, I was created by this industry, and I like to think I’m giving back. But I’m not giving back because I can make a scallop souffle, I’m giving back because I can make compost.” – Arthur Potts Dawson

What is composting?

Composting is the breakdown (or decomposition) of organic material (anything that was once alive) in the presence of oxygen (i.e. aerobic decomposition). Organic material can also decompose without oxygen, but this is slower and smellier, and tends to be called anaerobic decomposition or digestion (which can produce biogas). Healthy soil requires composted organic material.

Keep a little compost container in your kitchen for food waste, and empty it into your compost bin when it’s full.

The composting process involves tiny organisms, including bacteria, fungi, insects and worms. These organisms utilise the two main components of organic waste – carbon and nitrogen – and work in a series of stages. Insects, worms and other visible creatures break down organic material into a form suitable for microscopic organisms to act upon. The end result is a beautiful crumbly compost that contains a mix of minerals that plants can absorb as nutrients. There are many composting methods:

  • Basic heap – a pile of material
  • Enclosed containers (e.g. tumblers) – stop weed seeds blowing in
  • Digesters – e.g. the Green Cone system
  • Fermentation – e.g. the Bokashi system, suitable for flats
  • Leaf mould – keep leaves in a bin liner or in a separate pile; they take longer to break down (up to two years) but contain minerals the tree obtained from deep in the ground, that may not be found at the surface
  • Wormeries (also suitable for flats)
  • Composting using other critters

Plastic composter: fresh material is added via the lid at the top, and finished compost is removed with a spade via the hatch at the bottom.

A heap (loose or contained) – is the most widely used and least laborious process. There are plenty of purpose-built composters on the market, many available at subsidised rates from your local council. It’s also very easy to build your own from waste wood (e.g. pallets) and chicken wire.

Easily compostable:

  • Garden waste / grass cuttings / weeds / prunings
  • Kitchen waste – peelings, stems, stones, cores, anything that’s gone off
  • Tea bags and coffee grounds
  • Eggshells (smash them up first)
  • Fruit waste, including citrus peel
  • Paper (best if scrunched up)
  • Cardboard, middles of toilet rolls, corks, matchsticks
  • Human & pet hair
  • Wood ash – contains potash (don’t add too much though)

Basic composting advice for beginners, from the RHS.

Not-so-easily compostable:

  • Cooked food, meat, grease, bones, dairy produce – can attract vermin, but OK if you use the Bokashi method, Green Cone, wormery (only small amounts of animal products in a wormery), or if you make it vermin-proof with a strong container, car tyres, bricks etc. (having said that, lots of people add cooked food waste to compost bins, without attracting vermin)
  • Perennial or pernicious weeds – OK with Bokashi, Green Cone or wormery, or keep them in a bin liner until they are sludge, then add them to the heap
  • Diseased plants – again, OK with the above systems
  • Contents of vaccuum cleaner – usually inorganic, but OK if you have a natural-fibre carpet
  • Sanitary products – only if made from organic materials
  • Corks – take a long time

You can make your own compost containers from waste wood such as pallets, or you can buy or make slatted wooden containers like these (that look prettier). Note that there are two bins – one is added to until full, then it’s allowed to break down while you fill the other one; when that one is full you empty the first one, and continue the cycle. The slats make it easy to empty the bins when the compost is ready.

Not compostable:

  • Coal ash – won’t break down
  • Disposable nappies – contain inorganic materials
  • Plastic, glass, metal, polythene bags – or anything inorganic

Pet waste:

Vegetarian pet waste – fine; but most advice about dog or cat faeces will be to bin it rather than compost it, due to the risk of disease. However, landfilling dog or cat waste could lead to higher risks than home composting, as it may leach into groundwater, and it won’t break down very quickly in landfill because of the lack of oxygen. Again, many people successfully add pet waste to their compost bin – allowing the compost to break down for longer, and using the compost on trees or bushes rather than veg. See here for more information and advice.

Fresh organic matter recently added to the top of a compost bin – you can see fruit and vegetable peelings, eggshells, teabags, weeds, straw, paper and cardboard.

What are the benefits of composting?

In nature, plants die, break down and return to the soil, but when we grow food, we remove a crop that isn’t allowed to return to the soil. So we have to add something else if we want the soil to remain fertile – and the best thing is compost. It’s a wonderful soil improver, rich in nutrients, organic material and essential microbes to help your garden flourish.

Composting with critters 1: tiger worms.

Root systems of plants ‘grab’ the nutrients they need from composted materials in the soil, and (in the case of leguminous plants and nitrogen) from the air. Chemical fertilisers, on the other hand, are salts that are entirely water soluble, and their use causes several problems:

  1. Plants have to take them up when they take up water, so they become big and tasteless
  2. Plants don’t have to ‘work’ for their nutrients, so their root systems become weak and unhealthy
  3. Because they’re soluble, they leach from the land and cause pollution problems in watercourses
  4. They don’t add to soil structure, and so begin a downward spiral that requires more and more fertiliser
  5. They only contain nitrogen, phosphorus and potassium (N,P,K), not the large range of nutrients that compost does – like calcium, boron, magnesium etc, so plants suffer in the long-run
  6. The salts can kill some of the bacteria and fungi responsible for transferring nutrients to the plants, requiring ever-more chemical fertiliser

Composting with critters 2: cockroaches – really efficient converters, eat anything, don’t smell, shed their skin, which adds to the compost, and new cockroaches can be sold or given to pet shops for reptile food (they have to be contained of course – you don’t want them in your standard compost heap).

Other benefits of composting are:

  • Saves money on buying compost
  • Don’t need peat composts (which destroy peat bog habitats)
  • Reduces waste sent to landfill, so reduces harmful leachates (liquids) and methane (a potent greenhouse gas), and the need for fuel for trucks to transport it
  • Reduces the need for garden bonfires
  • Increases biodiversity in your garden
  • You can compost your confidential papers instead of shredding them!

Composting with critters 3: ‘grub composting’ with black soldier fly larvae – they can be ‘farmed’ on kitchen and garden waste to produce compost; the larvae fall into a collection chamber and can be fed to chickens or …….. cooked and eaten by humans.

What can I do?

Actually, you can’t stop dead organic materials composting, so you don’t have to do much really – you just have to organise your process so that it produces compost relatively quickly (unless you don’t mind how long it takes) and easily without any odours. If you have even the smallest of gardens or back yards, it really is something you should think about doing, rather than having organic material trucked away.

When choosing a site for composting, bear in mind that the process will be quicker in a sunny area, and directly on to soil. Composters can be placed in the shade or even on concrete providing there’s drainage (add a few spades of earth at the bottom to introduce necessary micro-organisms), but the process won’t be as fast.

Bokashi buckets are good if you have no space for an outdoor compost bin.

It’s important to include a roughly even mixture of ‘greens’ and ‘browns’. Greens are high in nitrogen and include vegetable matter and grass cuttings. Browns provide the carbon content – examples are dead leaves, small twigs, scrunched-up paper and cardboard. These browns are very important, as they also provide structure for the heap. Without them the heap would be too compact, oxygen could become depleted, and the heap could start to degrade anaerobically (resulting in a slimy, smelly end-product, giving off methane, a greenhouse gas).

Other forms of aeration can help. Traditionally this involves ‘turning’ the heap, but that can be hard work or impossible if it’s contained. Try pushing a broom handle through the centre of the heap and ‘stirring’ instead. Specialised tools for this task are available but not necessary.

A green cone, which can digest meat, bones, dairy products, diseased plants or perennial weeds and return them to the soil.

Your heap should have approximately 50% moisture content and the consistency of a wrung-out sponge. If it’s too dry, water it. If it’s too wet, add more ‘browns’. By following these guidelines, you should have compost formed at the bottom of your heap after approximately 6-9 months. If you’re in a rush add nettles, comfrey leaves, chicken manure or urine, all of which are compost accelerators. Pre-shredding your material also speeds up the process (but uses energy).

If you want to help others to compost more effectively, you could look into community composting, which may involve training for larger-scale composting and waste collection, and/or using the finished compost in public areas.

If you buy bag compost make sure you don’t contribute to the destruction of peat bogs, by buying peat-free compost instead.

For more complex composting strategies, there are specialist books and websites. You may also be interested in visiting our composting toilets topic. Finally, remember that there’s no such thing as ‘good compost’ – if it’s not good, it’s not compost.


Thanks to Scarlett Penn of WWOOF UK for information.

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