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Build your first hot compost pile with the right C:N blend

Microbes work fastest when carbon and nitrogen are balanced at about 30 parts carbon to 1 part nitrogen by weight, with enough moisture and air.

How

1. Start with 10 to 15 cm (4 to 6 in) of bulky browns at the base.
2. Use the C:N blend calculator to work out how much brown material each batch of greens needs. It works by dry weight, so it allows for your actual materials.
3. Volume rules of thumb disagree. The US EPA advises at least two to three times as much browns as greens by volume.
4. Colorado State Extension describes about two parts greens to one part browns, and the UK RHS suggests 25 to 50 percent soft green material.
5. Volume guides cannot allow for how dense or wet your materials are. If you want one volume rule, this site uses the EPA's, as food-12 does.
6. Layer greens and browns, always covering food scraps with 10 to 20 cm (4 to 8 in) of browns.
7. Chop tough items (corn cobs, stalks) to speed breakdown.
8. Water as you build so it feels like a wrung-out sponge. Most mixes should be no wetter than 55 to 60% moisture; activity slows below about 35 to 40%.
9. Leave out meat, fish, bones, dairy, fats, oils, pet waste, diseased plants, herbicide-treated plants, weeds with seeds (unless the pile reliably gets hot) and treated or painted wood.

Safety: Wear gloves when handling manure and compost, and wash hands afterwards.

Sources

1. Composting in Schools: C/N Ratio calculation. Cornell Waste Management Institute, Cornell University, accessed 2026-11
2. Composting in Schools: Getting the Right Mix. Cornell Waste Management Institute, Cornell University, accessed 2026-11
3. Composting At Home. US Environmental Protection Agency, accessed 2026-11
4. Composting. Royal Horticultural Society (UK), accessed 2026-11
5. Making Compost. Colorado State University Extension, accessed 2026-11

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