Welcome to the composting section, remember even a small effort by everyone can make a big difference.
Did you know that there are around 1 thousand million microscopic organisms in every teaspoon of compost?
Compost is a mixture of organic material and is used as fertiliser. Generally, the ingredients used to make compost come from our gardens and kitchens (food scraps) although organic material is anything that was once living. Compost results from the eventual decomposition or break down of the ingredients. It can take anywhere between two and 18 months before compost is ready to use. The length of time is governed by the method employed, what gets put into the bin, the time of year and how often the material is turned.
- Choose a site with care. Ideally, it should be warm and sheltered.
- Consider neighbours by siting the heap or bin away from any areas that are too close and could cause offence.
- To work properly, your compost heap should be at least 1m high x 1m wide x 1m deep.
- Start with a layer of coarsely chopped twiggy woody material on bare soil or grass.
- Add alternate layers of green matter (nitrogen rich) and brown matter (carbon rich) preferably in layers no more than 5-10cm deep (see list on page 5 of the Composting guide).
- Limit all materials, including grass clippings, to thin layers.
- If you can’t be bothered layering, just make sure there is a mixture of green and brown matter.
- Avoid cat/ dog/ human faeces, meat, fish, bones, oil and invasive weeds.
- Smaller pieces make quicker compost – for quick compost, fibrous materials should be no bigger than the thickness of your finger (2cm).
- The heap should have a cover, eg, plastic lid, rinsed underfelt, tarpaulin.
- Be aware that it is difficult to manage rodents if a compost heap is used.
- Rodents can be kept out of compost bins by cutting out a piece of chicken wire larger than the base of the bin. Place it underneath the bin on the soil and fold the edges 10cm up the sides of the bin.
When adding food scraps, it’s especially useful to add an equal quantity of brown material on top such as dry leaves to reduce odours.
Keeping it going
- Compost activators or accelerators can be added to the compost to hasten the natural break-down process. They usually contain a natural nitrogen or bacterial enzyme and can be bought at most garden centres.
- Sprinkling on lime and untreated wood ash can help balance pH & reduce smells.
- The heap should be as moist as a wrung out sponge. Add water if needed.
- Avoid excessive moisture by keeping the heap covered.
- To work properly, your compost heap needs to reach temperatures between 30 and 60°C. From time to time, check that it is heating up in the centre; it should feel warm.
- Compost needs air – turn and mix it up to aerate and speed up decomposition.
The final touches
- Once an open heap is 1 metre in height, you should finish it by turning it with a pitchfork and mixing it up every week or two.
- Either use a new bin for the new heap, or use your original bin and just keep the old heap covered with underfelt, tarpaulin or something similar.
- Compost is ready when it becomes a sweet, dark, crumbly material and you cannot distinguish the original materials in it.
- If compost is well maintained and turned often it can be ready in as little as 6-8 weeks. If it is never turned, it will be ready in 12-18 months.
- When it’s ready, put it onto the soil or dig it into your garden. You can also use it for pot plants and for potting up seedlings.
Don’t forget to wash your hands when you’ve finished composting and gardening!
Green and brown matter
GREEN – Nitrogen rich, wet matter
Fresh grass clippings
Weeds without seeds
Tea leaves and bags
BROWN – Carbon rich, dry matter
Bark, untreated sawdust
Twigs and sticks
What not to compost
Although in theory anything organic can be composted, some things are best avoided when composting at home.
Cat and dog faeces
Can cause disease
Meat, fish, oil, bones, fat
Can attract rats
Non-organics eg: tin, glass, plastics
Won’t break down
Invasive weeds, eg: kikuyu, wandering willy, jasmine
Could spread in or beyond your garden – however they can be composted after treatment (see page 7 of the Composting guide)
Large amounts of pine needles or gum leaves
Allopathic- create environment hostile to compost creatures
Woody materials in pieces larger than the diameter of your finger
Too slow to break down
Diseased plants (eg, with blight)
Disease may spread
Bamboo, flax and cabbage tree leaves
Not suitable for composting and not taken by composting companies (bury in the ground, or take to a transfer station for landfilling)
Common composting problems
Problem – Cause – Solution
Smelly, slimy heap
- Not enough air – Turn heap
- Too wet – Add brown material (eg. dry leaves)
- Too much nitrogen – Add brown material
Materials are not decomposing
- Heap too small – Increase size of heap
- Not enough heat due to lack of green materials or water – Add green materials (eg, manure or blood and bone) and water
- Materials in heap are too large – Break materials down into small pieces
Pests attracted to heap eg, flies, cockroaches, rats, mice
- Wrong food added – Don’t use meat/bones/ fish. Bury food scraps in centre of heap
- Bin not rodent proof – Rodent proof your bin
Fruit flies (vinegar flies)
- Heap is too acidic – Sprinkle lime on heap
- Heap is too dry – Add water and lime
Other “mini-beasts”, eg, beetles, worms
- This is not a problem – creatures are essential to the composting process. Appreciate the work they do!
It can be difficult for people to accept that well loved plants like honeysuckle and Mexican daisy are deemed to be pests, but it is essential to control them. Plants like ginger, jasmine and privet can cause serious harm to our native environment and others can threaten the livelihoods of producers of commercial crops.
How to compost invasive weeds
It is possible to compost invasive weeds, however it is essential that they first go through a “pre-compost” process in order to ensure that they die. This requires the following steps.
- Put the weeds in a large plastic bag with a handful of soil and water.
- Tie the top and leave for at least two months, until there are no green shoots or other signs of life.
- Add them to your compost heap as a green.
If you leave them for long enough, they will turn into soil. There is also another way to handle noxious weeds.
- Put them into a closed bin and cover them with water (or submerge them in a sack).
- Leave for 2-3 months by which time the water will turn a green/ brown colour but it can be used as fertiliser for your plants.
- Empty the solids into your compost bin.
Types of compost bins
Before you choose a compost bin you should consider what you will be putting in it. Larger, open bins are better for people with large amounts of garden waste. Smaller, enclosed bins are more suitable for households with large quantities of food waste as they provide a barrier to rodents. You may find you need both!
Choosing a bin
There are a number of points to consider before you buy a bin so that you get one appropriate for your needs. These are:
- the number of people in your home
- the size of your garden
- your ability to turn compost with a garden fork
- the bin design (ie, whether different parts need be lifted)
- the capacity of the bin taking the above into consideration
- materials used in the making the bin (eg, some are made of recycled plastic)
- whether the bin is made locally. If it’s hard on your back, your back needs to be up to it!
Make your own compost bin
If you are making your own bin, you can use a wide range of material, including chicken wire, wood, plywood, bricks, concrete blocks, etc. It must be on the soil and no smaller than 1m high x 1m wide x 1m deep and no larger than 5m3.
For large amounts of garden waste, units can be made from wood, bricks or concrete blocks. Ready access from the front is necessary.
Stacking bins have the advantage of being moveable and can be extended to cope with large amounts of waste. Black polythene or sacks may be used for lining, warmth and moisture control. Wrap netting frame around wooden stakes. Line these with newspaper or cardboard to retain heat.
Check for designs in books at your public library in books on compost such as The Suburban/Urban Composter by Mark Cullen.
Some designs can also be found at: