Set up a compost — from kitchen scraps to black gold

Compost isn't a rubbish heap, it's a reactor. Inside it, billions of bacteria, fungi and worms break your kitchen and garden material down into Humus — the dark, crumbly substance that makes soil fertile. A good compost heap smells of forest floor, not of rot. If it stinks, you're doing exactly one thing wrong — more on that in a moment.

In permaculture, compost closes the cycle: what grows in the garden returns to the soil as a nutrient. You don't buy fertiliser, you produce it — from things that would otherwise end up in the bin.

The only principle that counts: green and brown

Composting sounds complicated, but at its core it's a single mixing ratio. All organic material belongs to one of two classes:

• Green — moist and nitrogen-rich: kitchen scraps, grass clippings, fresh plant material, coffee grounds, manure. Gives the bacteria protein and energy.
• Brown — dry and carbon-rich: autumn leaves, straw, wood chips, cardboard, chopped branches, egg cartons. Provides structure, air and carbon.

The rule of thumb: roughly two parts brown to one part green (by volume). Layer up only green and you get a stinking, airless sludge — that's the one thing that goes wrong. Take only brown and you get a heap that does nothing for years. The mix is what makes the difference. Specialists talk about the C/N ratio (carbon to nitrogen) — ideal is about 25–30 to 1, and that 2:1 mix produces exactly that on its own.

What can go in — and what can't

Yes, gladly:

• Fruit and vegetable scraps, peelings, coffee grounds with filter, tea bags (without plastic)
• Grass clippings (slightly dried, not sopping wet in thick layers)
• Autumn leaves, straw remnants, wood chips, unprinted paper & cardboard
• Coffee grounds, eggshells (crushed), faded cut flowers
• Plant material from the beds (healthy — dispose of diseased separately)

Better not:

• Cooked food leftovers, meat, fish, dairy — they attract rats
• Root weeds (couch grass, ground elder) and seed-bearing weeds
• Diseased plants (Late blight, Clubroot) — pathogens survive the cold rot
• Citrus peel and walnut leaves in quantity (they inhibit soil life)
• Ash from treated wood, glossy paper, anything with plastic

Hot rot or cold rot?

There are two routes, and both work — they only differ in pace and effort.

Cold rot — the easy way

You add what comes up bit by bit, keep a rough eye on the green-brown mix, and let time do the work. After 9–12 months there's ripe compost at the bottom. No turning needed. Downside: the temperature stays low, weed seeds and pathogens survive. For most home gardens it's perfectly adequate.

Hot rot — the fast way

You collect material until you can build up about a cubic metre at once, well mixed and moist. The micro-organisms heat the core to 131–149 °F — that kills weed seeds and many pathogens. After 6–8 weeks, with two or three turns, it's done. Faster, more hygienic, but work. Hot rot needs mass all at once — which is why a three-bay system pays off.

The build — step by step

1. Location: part shade, directly on natural ground (not on concrete or plastic sheeting) — so worms and soil organisms move in from below. Close to the kitchen, or you won't use it.
2. Ventilation layer first: 3.9–5.9 in of coarse twigs or chopped branches at the bottom. That keeps the heap airy from below and prevents Waterlogging.
3. Alternate the layers: always a handspan of green, then a handspan of brown. Thin layers rot down better than thick clumps.
4. Keep it moist like a wrung-out sponge: not dripping wet, not bone dry. Water in dry spells, cover during prolonged rain.
5. Inoculate (optional): a few shovels of finished compost or garden soil bring the micro-organisms in directly.
6. Cover: a layer of leaves, straw or a compost fleece on top — holds moisture and warmth, protects against leaching.

When something goes wrong

• It smells rotten: too wet and too much green, no oxygen. Work in brown material (leaves, wood chips, cardboard) and turn it.
• Nothing happens: too dry or too much brown. Water it and add green material (grass clippings, kitchen scraps).
• Rats: cooked leftovers or bread in there. Leave them out, secure from below with fine wire mesh.
• Ants: the heap is too dry. Moisten it through.

How to tell it's finished

Ripe compost is dark brown to black, crumbly, smells of forest and no longer reveals the starting material (apart from a few hard pieces of wood — sieve those out and return them to the new heap). A simple test: sow cress on it. If it germinates quickly and green, the compost is ripe and not too "hot".

Use it as a 0.8–1.2 in layer on top of the bed (don't dig it in — the soil layers should stay undisturbed), as an addition in planting holes, or as a base for Compost tea. Half-ripe compost is enough for light feeders, while Heavy feeder like cabbage and squash love it fully ripe.

Alternatives for little space

No garden? Worm compost (a worm bin) turns kitchen scraps into high-quality fertiliser even on the balcony. Bokashi ferments kitchen scraps airtight in a bucket and is ideal as a first stage. Both complement the classic heap, but don't replace it in a large garden.

Thinking on from the compost

Compost is the hub — almost every other permaculture element connects to it. Its half-ripe material activates the raised bed and the hügelkultur bed. Think bigger and you can even draw warm water from the same rot — see the compost heater — or close the human nutrient cycle with a compost toilet. And for the in-between seasons, green manure keeps the soil alive.

In the Garden Planner the compost automatically gets a spot close to the kitchen in zone 2 — because a compost heap at the far fence never gets used.