Gardening - making compost

Compost is nature’s fertiliser. It is made from decomposed organic matter (anything that once lived). By putting your kitchen scraps and garden waste into your compost heap, you can create a sustainable, low-cost source of nutrients for your garden.

There are two types of compost heaps, hot and cold. A hot heap is assembled in layers like a lasagne, at a time when you have all the ingredients to hand. A cold heap takes up less space and is more likely the type of heap you will make at home by adding kitchen scraps and garden waste to your compost bin on a daily basis.

What you need to make compost

To make successful compost, you need:

• Something to put it in, such as an open-bottomed plastic bin with a lid, a sealed barrel that can be rotated (this works well if the barrel is on a stand), a metal, wooden or wire bin, or a free-standing heap (for bigger properties)
• Browns materials (that are dead or dry carbon-rich materials), such as dried leaves, sawdust, shredded newspaper or straw
• Greens materials (that are soft, green and leafy nitrogen-rich materials), such as fresh lawn clippings, soft green leaves, vegetable scraps, manure and weeds (these are fine to use in a hot heap as their seeds will be killed by the heat, but are best avoided in a cold heap.)
• Water – keep your compost heap moist, but do not saturate it
• Air – a compost heap needs ventilation. This can be achieved by turning it regularly, by making holes in your compost bin to let some air in, or by inserting an aeration pipe.

Cold compost heaps

A cold compost heap is made by putting kitchen scraps into a large compost bin daily, and covering these with a layer of garden waste (such as lawn clippings or dry leaves) or shredded newspaper.

By the time you have filled your bin to the top, the material at the bottom will have decomposed, and will be ready to spread on your garden. An opening at the base of your bin will help you to remove this material without disturbing the rest of the contents.

It is important to make sure that your compost heap is well aerated. Without air, anaerobic bacteria will get to work in your heap Then it will smell terrible and encourage the growth of fly larvae and maggots.

To aerate your heap, you can insert a cylinder of chicken wire or perforated PVC pipe down through the middle of the bin, and add your kitchen and garden scraps around it.

Hot compost heaps

A hot compost heap needs to be at least one cubic metre in size to maintain the ideal temperature needed to break down the materials into humus or compost. This high temperature will also kill weed seeds and plant pathogens (disease-causing organisms).

A hot compost heap is assembled in alternating layers of browns, greens and manure, like a lasagne.

Once assembled, the compost heap will start to heat up. After a couple of days, it will have reached a temperature of around 60 to 70 C. (This is because of the activity of the bacteria in the compost materials.) If turned regularly, it should break down into compost in just a few weeks.

How to make a hot compost heap

1. Position your bin or construct your heap in the shade, so that your compost doesn’t dry out.
2. Place a layer of straw or twigs at the base of your bin to aerate the bottom of the heap.
3. Place a layer of fresh grass clippings on top.
4. Add a layer of manure.
5. Water till moist (not saturated).
6. Progressively add layers of greens, browns and manure. (You need roughly four parts green to one part brown).
7. Gradually build up the compost this way, the thinner the layers the better.
8. Add water as you go. Remember to keep it moist, not saturated.
9. Keep layering until about one metre high.
10. Finish off with a final layer of straw.
11. Cover the compost heap to keep the moisture in. Some old carpet, cardboard or shade-cloth will do nicely.
12. Turn the compost regularly – every few days.
13. Water it if it gets dry.
14. You should have compost in about six to eight weeks (the time taken for the compost to break down will depend on how thick and woody the materials are).

Composting tips

• Try to keep the material as fine as possible.
• If you have a compost bin, you can build it up over a period of time. By the time the bin is full, you should have ready compost at the bottom of the bin.
• Lift up the bin and dig the decomposed material out from the bottom, then replace the bin over the rest of the heap. Keep filling from the top.
• Barrels produce compost more quickly because they are easier to turn.
• Your compost heap should get very warm, maybe even hot. This is normal.
• You can use meat and processed food, but this could attract vermin.
• Citrus fruits and onions take a long time to break down, but can be used if they are chopped finely.
• Adding soil to your compost heap will slow the composting process down and is best avoided.
• If your compost smells, it is probably too wet. Add dry material and turn your heap.
• Use your compost generously on all types of plants.

Where to get help

• Community or local garden groups
• Horticultural Therapy Association of Victoria Tel. (03) 9836 1128
• Cultivating Community Tel. (03) 9429 3084
• Department of Health Victoria, Prevention and Population Health.

Things to remember

• By putting your kitchen scraps and garden waste into your compost heap you can create a sustainable, low-cost source of nutrients for your garden.
• To make compost you need browns, greens, water, air and time.
• The finer the material you add to your heap, the sooner it will break down into compost.