If you want to become a great food gardener, you've got to get yourself a decent sense of humus. Humus is fully decayed organic matter. Soft, dark, spongy humus, the gardener's black gold, is the secret of healthy soil. And the healthier your soil, the healthier and more nutritious your plants. In nature, humus gradually builds up over thousands of years. This page is about how we get it faster. Yep, we can hit fast-forward on nature in our own backyards and in a word the way we do it is composting. Composting -- the art and science of using billions of tiny microbes to transform your food scraps and other organic waste into humus, the secret behind the sweetest tomatoes, the greenest silver beet, and the healthiest cabbage the world has ever seen.
Now you might already be squirming about the smell of compost, so let's get one fact straight: a well-managed compost smells good. It doesn't attract rats and cockroaches, it doesn't turn your neighbours against you, and it will be finished and ready to use within six or eight weeks. In fact, when your neighbours see what the compost does to your garden they'll be over to ask how you did it! For composting is the cornerstone of any sustainable vegetable garden.
As a living, breathing thing, the trick to a healthy compost pile is giving the microbes what they need. You'll be relating to these teeny critters in no time, as what they need is the right amount of three things that we need too: food, air, water and warmth.
This right here is where beginners can get it wrong. Because it's not just any organic matter than feeds a healthy compost pile, but the right combination of organic matter. A compost pile needs the right combination of foods high in nitrogen, which are often green and wet, and foods high in carbon, which are usually brown and dry.
|Foods high in nitrogen||Foods high in carbon|
Foods very high in nitrogen (activators)
blood & bone
Inside a healthy compost pile billions of tiny bugs are breathing. These bugs, or bacteria, breathe in oxygen, just like us. If the oxygen runs down the bugs change into bugs that can handle lower oxygen levels, called anaerobic conditions. These bugs are the bad guys and they do little farts and make bad smells. This is why a compost pile with too much nitrogen smells bad. The nitrogen makes the bacteria party hard, and their combined respiration uses up all the oxygen inside the pile, which sets the conditions for the bad guys of the microbial underworld. The result is also extra greenhouse gases like methane, which is what we don't want. If your compost smells bad you are losing nutrients to the atmosphere. But your nose knows a good compost pile.
To maintain enough air in your pile, you need to employ strategies like:
- poking holes in your pile
- resting your pile on a layer of courses branches and twigs
- turning your pile every four days or week with a compost fork, rotating compost bin, or compost aerator
- including about 5% course wood chips in your pile to make space for little air pockets (if it is all finely chopped material like grass clippings)
- incorporating a certain amount of more coarse material like small twigs and bark.
- running some slotted drainage pipe through the pile
Like us, the compost microbes need to drink. What they need, in fact, is a continuously moist medium in which to make their living. Not soaking wet, or tinder dry, but moist, like a freshly squeezed sponge. If your compost is too dry, add water, turning it to get the water in if necessary. If your compost pile is too wet, spread it out and and let it dry a bit before reforming, or mix in some dry stuff like shredded newspaper or dry pea straw.
Specific Ways of Composting
There are various ways you can meet the above aims to do with food, air and water. The most common are:
- Hot compost: stockpile organic matter, or source it in bulk, then build a pile of at least one cubic metre in size (any smaller won't work as the bugs need a minimum volume to create a critical amount of heat.)
- Placing organic matters in a tumbling compost bin
- Cold-composting: placing organic left-overs into a black plastic compost bin (it is best to drill holes in the side of these to let more air in) and layering them with straw or leaves
- Worm farms: worms make a fantastic compost. You can only feed them soft stuff, but they are more forgiving with getting carbon:nitrogen right, aerate the compost for you, and produce a wonderful product. See our page on worms...
- Chickens: chickens can be harnessed for your compost making work, and they'll thank you for the opportunity. There's nothing chickens like more than scratching through straw and food scraps for seeds and bugs and in the process they can create a great compost mix.
- Directly placing thin layers of organic matter under your mulch in your garden
Location, Location, Location
Just Have a Go
We run regular courses in compost and worms in Melbourne, a great place to learn more, and we'd love to see you. Check here for the next one.
Compost photo by Steven Rhall