What is Compost?
Quite simply it is a mixture of organic material that 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 decomposition or break down of garden and food scraps (organic material). It can take anywhere between 2 and 18 months before compost is ready to use. The length of time depends on the compost method used, what gets put into the bin, the time of year and how often the material is turned.
As the organic material breaks down, it changes and becomes what is known as humus. During the process, soil micro-organisms, worms and insects convert the organics into a soil-like material which can then be used in the garden.
The benefits of Compost
- It returns organic matter to the soil.
- It reduces the harmful effects of organic waste in landfill (e.g. water pollution, emissions of the potent greenhouse gas methane and bad smells).
- It reduces the need for chemical fertilisers in your garden.
- It reduces rubbish collection costs.
- It reduces the space needed for landfills.
- Producing your own compost saves money.
How to get started
- Choose a site carefully. Ideally, it should be warm and sheltered
- 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 5-10 cm deep
- If you cannot be bothered layering, just make sure there is a mixture of green and brown matter. NB: Smaller pieces make quicker compost
- Limit all materials, including grass clippings, to thin layers
- Avoid cat/dog/human faeces, meat, fish, bones, oil and invasive weeds
- The heap should have a cover e.g. plastic lid, underfelt, tarpaulin. Rodents can be kept out by cutting out a piece of chicken wire larger than the bin base. Place it underneath the bin on the soil and fold the edges 10cm up the sides of the bin
- Compost activators such as a dried blood and bone can be added to the compost to speed things up
- Sprinkling on lime and untreated wood ash can help balance pH and reduce smells
- The heap should be as moist as a wrung out sponge
- Avoid excessive moisture by keeping the heap covered
- To work properly, your compost heap needs to reach temperatures between 30 and 60ºC. 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
- 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
- Compost is ready when it becomes a sweet, dark, crumbly material and the original components are unrecognisable
- 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 is ready, put it on the soil or dig it into your garden. You can also use it for pot plants and for potting up seedlings.
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! There are a number of points to consider before you buy a bin. These are:
- The number of people in your home
- The size of your garden
- The capacity of your bin, taking the above into consideration
- Your ability to turn compost with a garden fork
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 a netting frame around wooden stakes. Line these with newspaper or cardboard to retain heat.
Frequently Asked Questions About Composting
What makes my compost smell?
- A compost high in nitrogen with no air will become acidic. Add carbon and turn your compost.
How do I keep rodents out?
- Add grass clippings to increase heat and turn regularly.
What can I not put in a compost bin?
- Do not put in meat, bread, heavy unshredded prunings (see "What not to compost").
How long do I have to wait until my compost is ready?
- A well maintained compost bin will produce compost in 3-4 months in summer, and up to 6 months in winter. However, times vary depending on the method, bin contents, time of year and regularity of turning.
Do I need to add water?
- If you add a 50/50 mix of nitrogen, materials which are wet, and carbon materials that are dry, it will be of a crumbly consistency.
How will compost help my garden?
- Compost feeds the soil, helps with water retention and encourages earthworms into your garden.
What is Bokashi?
Bokashi is a generic Japanese term, meaning 'fermented organic matter'. Widely used throughout New Zealand, Bokashi Compost-Zing turns household organic matter into highly productive garden compost in just four weeks.
Bokashi reduces organic waste volume, enhances soil condition, reduces odours and speeds up the rate of decomposition.
The system is often showcased at local and national Eco, Home and Garden shows. Bokashi is available through the Sustaining Hawke's Bay Environment Centre, organic product retailers, and various gardening outlets.
Not only is it easy to use, readily available, and environmentally friendly, it also gives you many advantages over regular composting:
- up to 50% quicker composting time
- less odour as the food decays
- increased growing power
- healthier and more productive plants
- requires no mixing
- produces a natural pour-on liquid fertiliser as well as physical compost.