Making Good Compost

The Alchemy of Composting

Compost is decayed organic matter — the product of millions of micro-organisms, fungi, worms, and invertebrates breaking down raw material into humus. A well-made compost heap transforms "waste" into one of the most valuable substances you can add to garden soil.

Good compost improves soil structure, feeds micro-organisms, retains moisture, buffers pH, suppresses disease, and provides a slow, balanced release of plant nutrients. It is the organic gardener's most important input.

The Carbon:Nitrogen Ratio

The key to good compost is the balance between carbon-rich "browns" and nitrogen-rich "greens":

Browns (carbon-rich): Cardboard, straw, dry leaves, wood chippings, newspaper, hay, bracken, untreated sawdust

Greens (nitrogen-rich): Fresh grass clippings, vegetable peelings, tea leaves, coffee grounds, fresh plant material, animal manures

Aim for roughly 3 parts carbon to 1 part nitrogen by volume. Too much nitrogen and the heap turns slimy and smells of ammonia. Too much carbon and it breaks down slowly without generating heat.

Building the Heap

Build in layers: a layer of browns, a layer of greens, repeat. Alternate in thin layers rather than adding large amounts of one material at once. Water if very dry. A well-built heap will heat up to 60–70°C within days — hot enough to kill weed seeds and pathogens.

What NOT to Compost

• Cooked food scraps, meat, fish, dairy (attract vermin)
• Diseased plant material (club root, blight-infected haulms, white rot — these survive the heap)
• Perennial weed roots (bindweed, ground elder, couch grass — these survive too)
• Anything treated with persistent herbicides

Turning and Timing

Turn the heap after 4–6 weeks — this aerates it, brings the outer cooler material to the centre, and accelerates decomposition. A heap turned 2–3 times will produce finished compost in 3–4 months in summer, or over winter. If you don't turn, expect 9–12 months.

Historical Perspective

Before the arrival of synthetic fertilisers (which became widely available after World War II, as ammonia factories converted from making explosives to making nitrate fertilisers), composting was not an "alternative" practice — it was the only practice. Every farm and household managed its organic matter carefully. The abandonment of composting in favour of bought-in synthetic fertilisers has led to catastrophic declines in soil organic matter, soil life, and soil structure across agricultural land worldwide.