Tips from a compost expert

Andrew Lucas knows a thing a two about compost. 

He manages our compost facility near Anakie, which composts up to 1000 tonnes of garden waste collected each week in our green-lid kerbside bins.

He also has his own backyard compost for fruit and veggie scraps from his family’s kitchen.

With backyard composting on the rise, we asked Andrew for some tips on getting started and some advice on what to do when it all goes wrong.

Let’s be clear….

To better understand how to successfully compost, you should first understand exactly what it is.

Compost by definition means “organic material that has gone through biological transformation using oxygen”. That means worm farming isn’t composting, Bokashi bins aren’t composting and dehydrators aren’t composting!

Composting done correctly uses oxygen – it’s an aerobic process.

These conditions are super attractive to a particular type of heat-loving bacteria called thermophiles. So while we say compost is ‘self-heating’, it actually gets hot because of a rapid and massive growth of these thermophilic bacteria.

During the compost processing, temperatures can reach 55 degrees and above, which pasteurises the compost, killing any harmful bacteria or microorganisms. It also breaks down any weed seeds.

Composting in your backyard is much different than our large-scale compost operation at Anakie where temperatures can actually reach 70 degrees and stay that way for a month! This means any microbial nasties such as Salmonella or Escherichia coli are well and truly dealt with.

Backyard composts don’t reach these temperatures because the smaller piles struggle to get the microbial population to heat up. We call them ‘cold’ composts because they break down due to non-thermophilic bacteria, kind of like fungi.

It all sounds complex, but it simply means you need to take more care with your backyard compost ingredients so your material actually composts, rather than slowly rotting away.

Let’s run through some of the common problems encountered in backyard composting:

  1. My compost is drying out
    If you’re composting fruit and veggie scraps, then you shouldn’t have a problem because of their high moisture value. However, over the summer months, grass clippings are dry and you may need to give your compost a good soak. The tiny bacteria and fungi that break down organic matter don’t work in a totally dry environment, so your pile of branches from tree pruning will look the same in 12 months if it’s not wet enough.
  2. My compost bin/pile smells
    You’re not putting enough carbon (dry matter) in your mix. Most of the material from our kitchen and garden has too much moisture and it’s also nitrogen rich. To get the right balance and stop unpleasant smells, you’ll need to add more carbon – think shredded newspaper, straw or sawdust.

    Also, avoid any foods that will smell and attract vermin. Your backyard compost is not the place for your meat scraps! Plus, as previously mentioned, you’re most likely to have pathogenic bacteria in your backyard compost and if it’s not getting hot enough, those micro-nasties aren’t being kept in check by the good guys.

    If you’re using an open pile, always top it with a cover of sawdust or straw. This carbon will actually capture the odour and is sometimes described as helping to keep vermin away, but don’t kid yourself; birds love to scratch around in a mulch-type cover and mice will squeeze in anywhere.

    Again, don’t put those high-nutrient fat and protein-based scraps in your compost to start with.
  3. My compost isn’t breaking down
    Your compost is actually a breeding and feeding ground for microbes. The more surface area on the ingredients, the easier it will be for them to start to consume it. If you build compost to their liking, they will come!

    Chop up woody plants and don’t expect large branches or logs to compost! The same goes for your kitchen scraps – broccoli stalks will still look like broccoli stalks if you don’t cut them into smaller pieces.
  4. Do I need to add anything to my compost?
    If it’s wet, add dry stuff (sawdust, shredded paper, straw etc.)

    If it’s dry, add water or wetter ingredients (fresh grass clippings, fruit and veggie scraps)
  5. How do I know when my compost is ready?
    It should look nice and dark (think 70% cocoa chocolate) and smell ‘earthy’. As compost ages the bacteria and fungi that break down woody materials exude that wonderful humus ‘earthy’ smell.
  6. Should I turn my compost?
    Turning it will help oxygenate the pile, although if you’ve got woody bits and pieces in the mix it’s probably getting plenty of air. The traditional compost bay designs work well as you essentially turn the compost as you move it along to the next bay. Turning material in an above-ground plastic compost bin is easy until it gets half full at which time you’ll give up unless you’re really after a workout!

Page last updated: Tuesday, 14 September 2021