Compost, step by step
Interactive lesson: from waste to humus — browns and greens, building a heap, hot and cold heaps, the compost corner, maturity and how much to use in the garden.
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The whole lesson as text
1. Browns and greens
Good compost doesn't just happen — you build it from the right ratio of browns and greens.
- Collect separate piles — Keep browns (leaves, straw, wood chip, cardboard) and greens (grass, kitchen scraps, manure) in separate piles until you build the heap.
- Aim for C:N 25–35 : 1 — Dry leaves have a C:N of 40–80, straw 80–120, fresh grass 12–25. The correct way is total carbon divided by total nitrogen.
- Weigh your bucket — Once, weigh a 10 L bucket (about 2 UK gallons) full of each material. Kitchen scraps: 5–6 kg; dry leaves, loose: 1–1.5 kg.
- Err towards browns — A heap with a little too much carbon just works more slowly. Chicken manure always goes in with browns, or you get ammonia, flies and lost nitrogen.
Why: Micro-organisms eat carbon as fuel and nitrogen to build their bodies. Too much carbon: the work is slow. Too much nitrogen: the heap stinks and the nitrogen escapes into the air as ammonia.
- Ratios don't average out: a bucket of leaves (C:N 60) and a bucket of grass (C:N 15) don't give 37, but something closer to 25–30.
- The rule “2–3 buckets of browns to 1 bucket of greens” works for kitchen scraps and leaves.
2. Building the heap
Moisture, air and size decide whether the heap heats up.
- Coarse base — 15–20 cm of coarse twigs or stalks at the bottom, for air from below.
- Layers and water — Build layers of 10–15 cm, browns and greens in turn. Wet each layer.
- Squeeze test — Squeeze a handful from the centre. 1–2 drops fall: 50–60 % moisture, ideal. A stream runs out: add straw or leaves. Nothing drips: too dry.
- Size and cover — Below about 1 × 1 × 1 m (roughly 3 × 3 × 3 ft) a heap rarely goes over 45 °C. Finish with a layer of browns and cover with a tarp, straw or boards.
Why: The micro-organisms in a hot heap need oxygen. Air comes from coarse pieces and turning, and a heap that is too small loses heat faster than it makes it.
- Pieces of 2–5 cm are ideal: finer material packs down, coarser material rots slowly.
- Water a dry heap while you build it, layer by layer — not from the top onto a finished heap.
3. The hot heap · Locked
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4. Cold compost and leaf mould · Locked
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5. The compost corner · Locked
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6. Maturity and use · Locked
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