To understand why it matters about where you put your apple core (and all the other compostable material your household creates each day) it helps to understand how foodstuffs break down.

There are two methods of decomposition: anaerobic and aerobic. Anaerobic stinks – both literally and for the environment. This is where material is broken down slowly by micro-organisms called anaerobes, which function without the presence of oxygen. Ammonia, rotten egg gas (sulfuric acid) and methane are by-products of anaerobic decomposition.

Methane is one of the greenhouse gases and is contributing to climate change and global warming. Indeed, when it comes to global warming, methane is 21 times more destructive than carbon dioxide.

Foodstuffs in landfill or overly wet, neglected compost heaps become anaerobic.
Where there is plentiful oxygen during composting – such as in a home compost bin – aerobic decomposition occurs quickly and efficiently, turning organic waste into humus without producing methane. By-products of aerobic composting include water and some carbon dioxide, but the main by-product is compost.

When compost is added to a garden it continues to do good by absorbing carbon from the atmosphere, locking it away in your soil. This ongoing storage process is a form of carbon sequestration, which is at the heart of some carbon emission trading schemes.

What to do

If you don’t already have a compost heap, start one. If you’ve had one before and failed, look at the new generation compost bins that include vents, which encourage good aerobic decomposition.

Keep a small bin or bucket in the kitchen at home and put all your vegie scraps in the bin for the compost heap. Consider encouraging schools and even work places to do the same thing.

As well as composting scraps, also add excess lawn clippings, prunings, leaves and shredded newspaper to your compost.


Winter workout for your compost heap

In winter, when temperatures are low, compost heaps often fall by the wayside. There’s lots of good material around at this time of the year to feed into your compost heap, so don’t let your compost languish.

If you haven’t ventured to the compost heap recently, get out there now and take your shovel with you. You are going to turn the heap. This is done to add more oxygen to your compost heap to form ideal conditions for aerobic micro-organisms. The easiest way to turn a heap is to shovel the contents of the heap into a new pile adjacent to the old one. If you have a compost bin, lift the bin up, then shovel all the material you’ve revealed back into the bin.

As you work, use the shovel to chop up any large bits of uncomposted material, such as orange skins or bits of green woody growth. This helps them to break down.

With more oxygen in the heap the aerobic activity multiplies, raising the temperature inside the compost heap and speeding up decomposition. To help the microbes along, add some animal manure to the heap as you are turning it.

The heat-loving or thermophilic micro-organisms that are active in a warm compost heap destroy disease-causing organisms and kill weed seeds, which makes your compost even more beneficial for your garden. In a well-functioning compost heap, the temperature at the centre of the heap can reach 70?C.

If your compost heap is very smelly, turn the heap as recommended but also add a few handfuls of dolomite lime to change the heap’s pH. If the heap is very wet, allow it to dry out – for example, leave the lid off the bin. Compost should be moist like a damp sponge, but not wringing wet.