How to compost your food scraps

Did you know that about 3 per cent of greenhouse emissions in our country come from organic matter rotting anaerobically (without air) in landfill sites? That might not sound like a lot, but this 3 per cent is equivalent to the annual emissions from Australia’s highest emitting coal-fired power station, or about the same as Australia’s entire aviation industry.

Once in landfill, organic waste produces greenhouse gases, predominantly methane, whose impact on the climate is 25 times more harmful than carbon dioxide.

We have the power to make a significant impact by doing two things: reducing or eliminating food waste by only buying what we need; and composting any leftover scraps.

How to make compost

Which composting method should you use and how do you compost in the first place? Regardless of which compost system you choose, they all require the same four ingredients:

1. Nitrogen: the fresh, juicy stuff such as food scraps, green plant waste and manure
2. Carbon: the dry stuff, including straw, old leaf mulch, shredded paper, brown cardboard (but no glossy magazine-type paper)
3. Air
4. Water

Choose the compost system that suits your situation best. Here are three options.

Worm farm
The humble worm farm harnesses the power of compost worms (Eisenia fetida). It can be homemade or bought from your local nursery or hardware store, and it can easily be tucked away in a large backyard or a balcony garden. It just needs good drainage, worm bedding (aged sawdust), a worm blanket (a damp hessian sack or cardboard) and a lid.

Compost bin
This is one of my favourite ways to compost food scraps. Got rodent issues? Dig the whole bin 20cm into the ground, or place it on free-draining bricks. Or cover the base with a layer of vermin mesh (aka aviary mesh) to stop rodents digging under and into your bin.

Trench composting
This is a super low-fi option for those with some garden space. It’s simply a matter of burying small amounts of food scraps in soil about 30cm deep. It’s not essential, but before you bury the scraps, mix in some dry carbon materials to prevent an airless environment from developing. Introducing air pockets between the soil and the carbon you’ve added means it won’t become anaerobic.

Getting it right

Whichever method you choose, what you need to focus on getting right is having a good balance between carbon and nitrogen to ensure you don’t attract flies or create a stinky (anaerobic) mess. So, in compost bins, for every one container of food scraps you put in, add two containers of carbon to cover them completely. For worm farms, once you have some worm bedding down, you can just add food scraps and cover with a worm blanket. However, when the worm farm is very young, it’s worth adding one container of carbon for every container of food scraps to help speed up the process.

As gardeners, we’re in a unique position to turn a ghastly problem into a nourishing solution. Every time you divert food scraps to compost systems instead of landfill, know that you’re not only helping to grow a better garden, but you’re also helping to grow a better world.

Read more about composting here.

Photo by Natalie Mendham