Compost is one of my favourite garden activities and topics of discussion. I’ve been composting for years and my kitchen scraps and garden waste all go into the mix which is home to many of the animals in my life – of the invertebrate persuasion.
My local council is in the process of changing their Waste Collection and Recycling Services and as far as I can make out composting isn’t a part of the new strategy. Composting was undertaken in the previous Single Bin Recycling system, but I’d like to see the City of Stirling encourage composting on an individual basis. South Australia is recognised for its progressive waste management and recycling. Local councils promote composting of food scraps, both at a household level with a kitchen bench-top system for composting kitchen waste and at a municipal level with a green organics bin for garden and kitchen waste.
Compost is the best thing to enrich soil, because its recycled organic matter and it doesn’t cost anything to make – just a bit of rubbish sorting and time for it to ferment . Any organic matter can be recycled through composting eg.
- food waste from the kitchen
- lawn clippings, weeds, prunings, etc from the garden
- newspaper, tissues, paper towels
- contents of vacuum cleaners
With the correct ratio of carbon to nitrogen hot composting occurs. The temperature starts around 20-30ºC and mesophilic bacteria (which like medium temperatures) break down material. They eat and multiply, producing water, carbon dioxide and heat. As the heat increases thermophilic bacteria start working on the material and they like temperatures of 40-70ºC, which is when the compost heap cooks and kills any weed seeds or diseased plant material. Both of these are aerobic bacteria and will only live, eat and multiply if there is enough oxygen, thus aeration is essential. Anaerobic bacteria will break down material if there is no oxygen, but you don’t want this happening because they smell bad. Aerating the heap keeps anaerobic bacteria away . I have a compost aerator which is a metal pole with a spiral at one end. Any time the compost gets smelly I twist the aerator into the heap and pull it out, mixing up the ingredients and adding oxygen. These days I aerate the compost heap more often than I used to and it doesn’t get smelly.
After the food for the bacteria runs out, the temperature decreases and macroscopic invertebrates (earthworms, earwigs, mites, etc) return to do more eating . These are what I see when I use the compost aerator or turn the heap. But it’s not over yet; the compost is still raw and needs maturation.
“Once the worms start to disappear, you know the compost is almost done. At this stage it’s considered ‘cooked’ and ready to use. Your compost should look like rich chocolate cake – dark brown in colour, moist and crumbly.” 
It’s a good idea to contain compost, although it isn’t essential for it to be covered. Any large old container or a purchased compost bin works well. I always have two compost bins at different stages of decomposition on the go. If you have the space and enough ingredients, more heaps will speed up the process.
I recently turned my two compost bins and spread the finished compost on my winter vegetable garden bed. I love the smell of compost, rich and earthy and just what my garden needs. Digging compost in helps soil retain water, as well as adding important nutrients. When turning the heap, i sieve the finished compost and anything not decomposed goes back into the heap, along with all the earthworms and other critters I disturb.
When I spread compost on my garden beds, all sorts of plants pop up: tomatoes, lettuce, capsicum. When I talk about compost tomatoes, I haven’t removed them from the compost after they’ve rotted a bit, as someone once thought. I don’t mind that my compost doesn’t get hot enough to kill seeds, I know not to put nasty weeds in the mix and my cold compost just takes a bit longer .
Four weeks after spreading compost on the winter vegie garden bed and planting snow pea seeds, they are off to a good start. I also planted lettuce and onion seedlings.
- Taylor & Taylor (1993) The Compost Book Sydney: Reed
- Heywood (2005) Composting: From Organic Waste to Black Gold Melbourne: Penguin