Get that garden compost really cooking

Get that garden compost really cooking

Hot composting is great for processing bulk organic matter, pathogens (bad bugs) and weeds and involves building a compost pile (in one go) at least one cubic metre in size.

Any less than this and it won't generate the heat required to break down the organic matter and kill off pathogens in the desired timeframe. Hot compost will easily get up to over 100 degrees, however the ideal temperature is 60/65 degrees. At this level it's killing off pathogens but not the beneficial microbes. Above this and the good microbes are killed as well.

There are two things that all composting methods have in common and the first is the ingredients.

There are four universal inputs: carbon, nitrogen, water and air. Carbon is anything dry and brown (think dead) like straw, hay, brown leaves, shredded office paper, ripped/scrunched newspaper or cardboard. Nitrogen is anything really fresh including animal manures (horse, cow, chicken, sheep, rabbit etc but leave out cat poo due to the risk of toxoplasmosis), green lawn clippings, food scraps and green waste.

Things that should never go in compost include invasive grass species (twitch and kikuyu and seed heads from unwanted plants).

The second common feature is that these ingredients are layered. Just like a lasagne, the carbon and nitrogen materials are layered, alternating between the two until you've reached at least one cubic metre.

Most compost books advise a carbon/nitrogen ratio of 25:1. However it really depends on the materials you have on hand. You'll find that very rarely will any of them actually be 100 per cent carbon or nitrogen.

We find a 50:50 ratio works well, with sometimes a little less nitrogen and more carbon when we have ingredients rich in nitrogen.


Get yourself a thermometer and learn what 60/65 degrees looks/feels like. Once you're feeling comfortable with the process your eyes and fingers do the job well.

We cover our piles with a thick layer of straw to prevent the outside drying out. However, if you live in high rainfall areas you may need to cover with tarps. We also make free-standing piles with no infrastructure so they are easier to make and turn.

You need to turn the pile to make sure it 'cooks' evenly. When you actually turn it is determined by how quickly/slowly it reaches the desired temperature (60/65 degrees). This often happens within 24 hours, other times it can take up to seven days - it depends on the inputs. Generally it's once a week, but the more experience you get the more you will refine your practices.

Compost activators will inoculate the compost pile with their nutrients, giving it a serious BOOST. Common activators include plants (comfrey leaves, dandelion, stinging nettle, yarrow leaves, tansy leaves) which have especially high levels of key minerals. You can also use mature. microbe-rich (healthy) compost or road kill which will attract microbes.

When it's ready:

  • It's the colour of 70 per cent dark chocolate
  • It's fluffy and has good 'crumb' structure. It doesn't feel sticky/muddy or dry and sandy.
  • When you squeeze a handful of it, one drop of water (no more) comes out of it indicating it has the right moisture content.
  • It smells sweet and earthy


Smelly: It's too wet and likely anaerobic (not enough air). Mix in more carbon, a touch of lime and turn to help restore balance.

Infested with ants: It may be too dry. Add water; cover exposed food scraps on top with carbon and hessian/felt and turn the compost.

Not breaking down: Not enough nitrogen materials. Add more rich materials (food scraps, manure, green lawn clippings) and turn the pile to add more air.

Swamped with small black flies: Cover any exposed food scraps with carbon.

Visit Soil and Health for more.