Composting & Soil Health

Soil is not just dirt

Healthy soil is a living system. By volume it is roughly 45% minerals (sand, silt, clay), 25% water, 25% air, and about 5% organic matter — yet that small organic fraction does most of the heavy lifting.

Dirt is what you sweep off the floor. Soil is alive: it breathes, holds water, cycles nutrients, and supports the roots that feed everything above ground.

A handful is a metropolis

• A single teaspoon of healthy soil can hold billions of bacteria, plus fungi, protozoa, and nematodes.
• Fungal threads (mycelium) weave through soil, linking plant roots and trading nutrients for sugars.
• Earthworms, beetles, and mites shred material and mix the soil, building structure as they move.

The soil food web

Plants release sugars from their roots to feed microbes. Those microbes unlock minerals and feed larger creatures, which are eaten by larger ones still.

This web is what turns dead leaves and food scraps into plant-available nutrients — and it is exactly what composting puts to work on purpose.

Reading a soil profile

Dig down and soil reveals layers, called horizons: a dark organic surface (O), rich topsoil (A), subsoil (B), weathered parent material (C), and bedrock (R) below.

• The dark topsoil near the surface is where most life and organic matter live.
• Building topsoil naturally takes centuries — compost lets you build it in seasons.

Composting is managed decay

Composting is simply decomposition that you steer. Microbes break complex material into stable, dark, crumbly humus that smells of fresh earth.

Your job is not to do the work — it is to give the decomposers the conditions they want, and they do the rest.

The four ingredients

• Carbon (“browns”): the energy source — dry, woody, papery material.
• Nitrogen (“greens”): the protein — fresh, moist, living material.
• Oxygen: microbes need air; without it the pile turns sour and slow.
• Water: moist like a wrung-out sponge — damp, never soggy.

Browns and greens

The single most useful idea in composting is the carbon-to-nitrogen (C:N) ratio. Microbes thrive at roughly 25–30 parts carbon to 1 part nitrogen.

In practice, aim for about 2–3 parts browns to 1 part greens by volume, then adjust by smell and feel.

Why a pile heats up

As billions of microbes feed, they release heat. A well-built pile climbs to 55–65°C (130–150°F).

That heat is useful: it speeds decay and kills most weed seeds and plant pathogens.

Pick a method that fits your life

There’s no single “right” way to compost. Choose by your space, time, and what you want to compost.

• Cold pile: easiest. Add as you go; finished in 6–12+ months.
• Hot pile: fast and weed-killing, but needs bulk and turning; weeks to a few months.
• Tumbler: tidy and rodent-resistant; good for small yards.
• Worm bin (vermicompost): indoor-friendly; red wigglers eat food scraps.
• Bokashi: ferments scraps in a sealed bucket — even meat and dairy — then buried to finish.

Build a hot pile, step by step

Make it big enough to hold heat: at least about 1 cubic metre (a 1m × 1m × 1m / 3ft cube).

1. Lay coarse browns (twigs, straw) on the bottom for airflow.
2. Alternate thin layers: ~2–3 parts browns to 1 part greens.
3. Dampen each layer to wrung-out-sponge moisture.
4. Finish with a brown layer to cap odours.
5. Turn after about a week, then every 1–2 weeks.

Great compost fodder

Leave these out (home piles)

• Meat, fish, dairy, and oily/greasy food — attract pests and smell.
• Dog and cat waste — can carry pathogens.
• Diseased plants and seeding weeds — unless your pile runs reliably hot.
• Glossy or coated paper, and chemically treated wood.

The three dials

Once a pile is built, you manage three things: air, moisture, and balance.

Turning adds air and resets hot spots. Watering or adding greens fixes dryness. Adding browns fixes wet, smelly, or slimy piles.

Quick diagnosis

• Ammonia smell → too much nitrogen → add browns.
• Rotten-egg smell → too wet / airless → turn and add browns.
• Not heating up → too small, dry, or low nitrogen → add greens + water; rebuild bigger.
• Flies or pests → exposed food → bury scraps, cap with browns.
• Soggy and matted → too wet → turn, add bulky browns, cover from rain.

When is it finished?

Compost is ready when it’s dark and crumbly, smells like fresh forest floor, and you can no longer recognise the original ingredients.

Let it cure for 2–4 weeks before use so it stabilises and won’t rob nitrogen or burn young roots.

Putting compost to work

• Top-dress: spread 1–3 cm over beds and let worms pull it down.
• Potting mix: blend roughly one-third compost with other media.
• Mulch booster: layer under wood-chip mulch to feed the soil slowly.
• Compost tea / extract: steep finished compost to inoculate soil with microbes.

Five principles of soil health

Healthy soil isn’t built by compost alone. These five principles, drawn from regenerative growers, keep soil alive year-round:

1. Minimise disturbance — dig and till as little as possible.
2. Keep the soil covered — use mulch or living plants.
3. Keep living roots in the ground — they feed the microbes.
4. Maximise diversity — mix crops, cover crops, and plant families.
5. Integrate organic matter — compost, mulch, and residues.

The bigger picture

Every bucket of scraps you compost is carbon kept out of landfill, where it would otherwise release methane.

Returned to soil as humus, that carbon improves water holding, feeds life, and is locked away from the atmosphere.

That’s the full picture

You’ve now read what living soil is, how composting works, how to build and fix a pile, and how to turn the result into lasting soil health. Scroll back any time to revisit a section.