Compost for the environment

Composting is great for the environment and your garden. It cuts down household waste, reduces greenhouse gas emissions, and improves soil organically. Best of all composting systems can be cheap to set up, easy to run and fit almost anywhere.

There are a variety of composting methods and ways to contain your organic matter – from a simple heap, pit or enclosure to bins, barrels and worm farms. All have their advantages and varying reasons for use.


Food and garden waste in landfill produces methane gas, which as a greenhouse gas is 21 times more potent than carbon dioxide. Also by reducing the need for transporting such waste, less fossil fuels are burnt, which means less greenhouse gasses and pollutants in the air.

Sending organic rubbish to landfill is also a waste of good composting material, which is essential in building good, healthy soil.

Compost is excellent for improving the structure of poor soils by increasing drainage in heavy clay soils, containing water in light sandy soil, increasing aeration in compacted soil, preventing surface crusting in silty soil, and keeping soil cool in summer and warm in winter.

While composting is great for households with a backyard and room for a compost bin or heap, worm farms are ideal for smaller places. Worm farms are excellent for small areas like balconies and courtyards because they are compact and relatively tidy. Worm castings (excrement) and juice (liquid runoff) make an excellent organic soil conditioner and fertiliser for the garden and potted plants.

Creating compost

There are two different types of decomposition that occur when composting – anaerobic and aerobic. Anaerobic means decomposition occurs without oxygen. Throughout this process, decomposition can be slow, smelly and produce methane.

Aerobic decomposition relies on oxygen to break down organic matter. This process is faster, less smelly and is less likely to produce methane. An aerobic system is ideal and to do this you need to create the right conditions for your compost.

A good compost needs microorganisms (bacteria and fungi), which in turn need oxygen from air, nitrogen and trace elements from organic ingredients, water and a little time.

Oxygen helps the organic matter heat up and therefore break down faster. In ideal conditions the temperature will rise to about 60 degrees Celsius in the middle of the heap. As the organic matter breaks down the heap will shrink to about one third its size. When the temperature cools, earth and compost worms invade the heap to further break down the material.

Setting up a compost system

Whether you use a bin or just a simple heap, compost systems ideally need to be set up on a sunny, well drained spot that receives some shade in summer. Although compost decomposes faster if it is hot, it is important that it doesn’t dry out.

Add about a spade full of compost from a previous batch or some garden soil to help introduce good microorganisms into the heap.

If you are using a bin, ensure you line the base with wire mesh to keep rats and mice from burrowing into the organic material. Another vermin deterrent is burying the bin a few centimetres into the soil or building some soil up around the edges of the bin.

Add a layer of sticks or large prunings to the bottom of the heap to help create space for air circulation.

Composts needs to be kept moist, like a damp sponge. Ensure the top of the organic material is protected by a layer of cloth, old carpet, underfelt, old clothes or a plastic sheet.

If you are using a bin, ensure its lid has small holes to let the rain and air through.

What to add to compost

The more different varieties of organic matter added to a compost, the richer it will be. Almost all organic matter can be added to a compost bin, however, if you are just starting out with composting steer clear of meat, fish, dairy and fats because they attract vermin.

A good mixture of elements for a compost is about 20 parts carbon to one part nitrogen. High carbon or brown ingredients are: dry leaves, twiggy prunings, sawdust, paper, straw, dry grass, wood ash, shredded paper and ripped up cardboard.

Ingredients high in nitrogen or green ingredients are vegetable and fruit scraps, fresh lawn clippings, farm animal manure (no pet droppings), old vase flowers, garden clippings, coffee grounds, tea leaves and seaweed. However, before taking seaweed from a beach get permission from the local council first

Other wastes that can be composted are hair, fluff, vacuum cleaner dust, used potting mix, crushed egg shells and old clothes.

Improving aeration

Turning the compost frequently is essential for getting good aeration into the mix and helping it heat up. This can be done with a shovel, garden fork or compost corkscrew. You can also insert a piece of plastic agricultural pipe with slits or holes into the centre of the heap to help bring air into the organic material.

If your bin is a closed plastic bin drill small holes in the side to improve aeration. Use fly wire on the inside of the bin to cover the holes and prevent flies from entering.

Compost worms will also help turn your compost and aerate it.

Some ingredients that help activate the heat in compost are fresh grass clippings, comfrey, farm manure, urine and seaweed.

What not to add to compost

Although some compost systems can get quite hot, they rarely get to temperatures that can properly kill off weed seeds and diseases. To ensure you don’t spread such nasties, keep weed seeds and disease infected plants out of the heap.

If you do want to add them, kill off the seeds and diseases first by placing them in a sealed clear plastic bag in the sun for a few months before adding them to the heap.

Fruit fly infested fruit should also be boiled or sealed in a plastic bag and stored in the sun for at least a week before composting.

Don’t add large amounts of salty water because salt is no good for soil or plants. Large woody prunings also take too long to break down and excrement from humans and meat eating pets (dogs and cats) is not recommended because it may contain harmful bacteria or intestinal worm larvae. However, it is possible to compost the bedding from vegetarian pets like rabbits and guinea pigs.

Composting methods


This technique is good if you plan to constantly add organic matter to the system. Add alternate layers of green and brown materials and try to add a thin layer of soil and a handful of fertiliser such as blood and bone on top of each layer. The heap will continue to shrink, allowing more space for extra organic matter.

All in together

This method is good if you have all of your ingredients ready. Combine kitchen and garden waste, plus fertiliser at the same time. Turn several times a week to generate a lot of heat to break down the pile quickly. Tumbler style compost bins are ideal for this method of composting because the tumbler method makes it easy to turn the bin regularly.

When is compost ready?

A good compost can break down within about four to 10 weeks but it does depend on many different variables such as climate, ingredients and care.

Compost is ready when there are no recognisable pieces of the original organic material. The organic waste will be converted to a dark brown, crumbly, sweet smelling earth-like substance that should contain plenty of worms.

Add compost to your garden or pot plant soil, or use it as mulch on the soil’s surface. To avoid fungal decay don’t pile compost up against tree trunks or plant stems.

Trouble shooting

Although composting is relatively easy, there are a few things that can go wrong.

Smelly compost

A smelly compost can mean it is too wet or not getting enough air. Fork in dry leaves, shredded paper or garden mulch and make sure you turn the heap regularly to increase air circulation.

A common cause can also be too many food scraps and not enough dry ingredients. Too many nitrogen rich ingredients will cause the heap to get acidic. To reduce acidity add garden lime, dolomite or woodfire ash.


A good balance of worms, slaters, ground beetles, bacteria and fungi are welcome visitors to a compost. However creatures such as ants, cockroaches, flies, spiders, mice or rats are not so welcome. Ensure food scraps are covered by a layer of garden mulch and then covered and enclosed by a lid. Weigh the lid down with a brick or stone. This should keep mouse and rats out. Vermin can be attracted to the warmth generated by decomposing compost, ensure the bottom of the bin is lined with wire mesh to prevent them from burrowing into the heap from below.

A dry compost attracts ants and cockroaches and encourages an over abundance of slaters. If this is the case, moisten the compost and turn often to discourage such pests.

Meat, dairy and seafood attract vermin so keep this out of the heap. If you add baked products such as old bread, soak it in some water until it is a gooey mush and bury it deep within the compost. This will make the food less attractive and harder to find for animals.

Although small vinegar flies are harmless and a sign of acidic conditions, blow flies indicate meat, dairy, or seafood – again remove and do not add to the heap.

Spiders under the lid are attracted to the invertebrates and small flies in the compost. Put a handle on the lid, check for spiders before placing your hands under the lid and wear gloves.

Slow to mature

If your organic matter doesn’t seem to be decomposing fast enough it could be because it is not hot enough or it is not getting enough air or water. To fix this problem add more nitrogen rich material such as kitchen or green garden organics to speed up the composting process. Turn the heap and add water.

If the heap gets too cold in winter, try covering it with an insulating material.

Common types of compost systems

Compost bins: come in a variety of shapes and sizes. They are usually made from recycled or new plastic, and bottomless. It can be difficult to turn the material in the bin – using a garden fork or compost corkscrew can help. Also lifting the bin off the heap and turning it then returning the compost to the bin can be another way.


Compost barrels: generally cylindrical plastic or metal bins that rotate on a frame. The drum opens at the end or on the side and contains air vents for oxygen circulation. They either rotate on their sides or are turned upside down to aerate the compost. Providing the bin is not too full and heavy, it can be quite easy to turn and is a better option for people who physically struggle to turn compost.

Enclosures: can be made from any simple structure, like timber, chicken wire, bales of hay or railway sleepers to enclose the compost heap. This method is very low tech and cheap to produce, however, it is not very vermin proof or portable.

Compost heaps: very low tech, economical and easy to build. Heaps require nothing more than roughly one square metre of space on soil, preferably in a sunny spot. Again, not vermin proof or portable and a little messy for the tidy conscious.

Pits or trenches: this is probably the simplest method of composting because you just need to dig a hole and place the organic matter into it. Cover the hole with soil and the organic matter will eventually break down.

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