Composting Guide for Australian Gardens

Hot, cold, worm farming, and Bokashi methods with troubleshooting tips

Compost is the foundation of a productive garden. It improves soil structure, feeds soil microbes, retains moisture, and provides slow-release nutrients to plants. Making compost turns kitchen scraps and garden waste into the best soil amendment you can get, and it is free.

This guide covers the four main composting methods, the carbon-nitrogen ratio that makes compost work, and how to fix common problems.

Composting Methods

Hot composting

The fastest method. A well-built hot compost pile reaches 55 to 65 degrees Celsius internally and produces finished compost in 6 to 8 weeks. It kills weed seeds and pathogens.

1. Build a pile at least 1 cubic metre in size (smaller piles will not heat up properly)
2. Layer carbon-rich materials (brown) and nitrogen-rich materials (green) in a roughly 3:1 ratio by volume
3. Moisten each layer as you build (the pile should feel like a wrung-out sponge)
4. Turn the pile every 3 to 5 days when the temperature drops below 45 degrees
5. The pile is finished when it stops reheating after turning and looks like dark, crumbly soil

Cold composting

The lazy method. Add materials as you have them, let nature do the work, and wait. A cold compost pile takes 6 to 12 months to break down but requires almost zero effort. Just keep adding scraps and garden waste on top and let it rot.

Cold compost does not heat up enough to kill weed seeds, so avoid adding weeds with seeds. Otherwise, almost any organic material can go in.

Worm farming

Compost worms (red wrigglers or tiger worms) process kitchen scraps into nutrient-rich castings and liquid fertiliser. Worm farms are compact, odourless when managed properly, and perfect for small spaces.

• Buy or build a tiered worm farm with drainage
• Start with 1,000 to 2,000 worms
• Feed small amounts regularly (the worms will eat roughly their own body weight per week)
• Avoid citrus, onion, meat, dairy, and oily foods
• Keep the farm in a cool, shaded spot (worms die above 35 degrees)
• Dilute the liquid (worm wee) 10:1 with water as a liquid fertiliser

Bokashi

A Japanese method that ferments kitchen scraps (including meat and dairy) using specific microbes. Not true composting, but a fermentation process that pre-digests food waste before it goes into the soil or a compost bin.

• Add kitchen scraps to a sealed Bokashi bucket, sprinkling Bokashi bran between layers
• Press down to remove air pockets. Keep the lid sealed
• Drain the liquid every few days (dilute 100:1 as a fertiliser)
• Once the bucket is full, leave sealed for 2 weeks to complete fermentation
• Bury the fermented contents in a trench in the garden or add to a compost bin to finish

Carbon-Nitrogen Ratio

Good compost needs a balance of carbon-rich materials (brown, dry) and nitrogen-rich materials (green, wet). The ideal ratio is roughly 25 to 30 parts carbon to 1 part nitrogen, but in practice, just aim for about 3 parts brown material to 1 part green by volume.

Carbon-rich (brown) materials

• Dry leaves
• Straw and hay
• Cardboard and newspaper (shredded)
• Wood chips and sawdust (in small amounts)
• Dried grass clippings

Nitrogen-rich (green) materials

• Fresh grass clippings
• Kitchen scraps (fruit, vegetables)
• Coffee grounds
• Fresh garden prunings
• Animal manure (chicken, cow, horse)

Troubleshooting

Compost smells bad

Smells like ammonia or rotten eggs. Too much nitrogen (green) material and/or too wet. Add dry carbon material (shredded cardboard, straw) and turn to add air. The smell should clear within a day or two.

Compost is not heating up

Pile too small (needs at least 1 cubic metre), too dry, or not enough nitrogen. Add nitrogen-rich material (fresh grass clippings, chicken manure), moisten, and turn. Ensure the pile is at least 1 metre in each dimension.

Compost is attracting flies

Exposed food scraps attract vinegar flies and blow flies. Always bury fresh kitchen scraps under a layer of carbon material. Cover the top of the pile with a layer of straw, dry leaves, or cardboard.

Compost is too dry

Add water while turning. The pile should feel like a wrung-out sponge throughout. In dry Australian climates, you may need to water your compost pile as regularly as you water the garden.

Frequently Asked Questions

Related Guides

Fertilising Guide

Mulching Guide

How to Build a Raised Garden Bed