The Compost Conversation – an homage to the bacteria

Mikaela Beckley looks at her compost through 400x magnification.

Over the next few weeks we thought it would be fun to take a deep dive into the microscopic world of our compost piles and meet some of our composting microbes.

As composters we could see ourselves as microbe farmers, as like any farmer worth their salt we aim to provide our microbes with a balanced diet, adequate fresh air and enough water to drink and swim around in. Unlike most farmers, we can’t actually see most of our charges, so we rely on our senses (smell, touch, sight) and temperature (if hot composting) to tell us if all is going well for them.

This week we will look at bacteria. These teeny single-celled organisms are the bottom of almost every food chain on the planet, including our compost, and as such are incredibly important, and numerous. There are over one billion bacteria in a single teaspoon of compost! This makes bacteria the largest number and weight of any of our compost microbes.

So, let’s go microscopic and take a look!

Down here we can see bacteria of all shapes and sizes everywhere, jiggling around the soupy surface of particles of organic matter.

While some can move themselves around, most have to hitch a ride on, or in, an earthworm to get to different regions of our compost pile.

The bacteria we raise in our compost piles prefer an easy to digest diet, so for them we add things like coffee grounds, manure, leafy greens and, of course, kitchen scraps. Our bacteria are very talented at extracting nutrients, such as nitrogen, from their food and using them to build their bodies, making them very nutritious morsels indeed (more on this next week). But our bacteria also need adequate water, remember the squeeze test, and adequate oxygen available to them throughout our piles to keep them alive and happy.

A happy bacterium can replicate itself within 20 mins, and as it does it releases a tiny bit of heat. Multiply this process of replication by the billions and we start to see how our compost can heat up to 55 degrees Celsius and above in no time at all. In our hot compost piles this heat not only kills weed seeds, it also takes care of any potentially disease-causing bacteria lurking around.

While bacteria are simple folk (literally a single cell and a few enzymes), they are busily working away, simultaneously decomposing our compost ingredients while gluing tiny particles together (microaggregates) to improve its structure. This allows for water and oxygen to penetrate more effectively and increases the water holding capacity of our compost and eventually our soil.

So, thank you little ones, we salute you!

Next week we will meet bacteria’s trusty partner in quality compost making, fungi, and see why bacteria are good enough to eat!

– Mikaela Beckley works with Yes In My Back Yard, (YIMBY*), a community-scale composting initiative in Castlemaine and surrounds. Send questions or comments to