Contents
Greens, browns, turning
A working home pile needs two inputs: nitrogen-rich greens and carbon-rich browns, mixed in a proportion near 25 parts carbon to 1 part nitrogen. Keep the air and water balance right and the heap holds 54-71 C until the material breaks down into humus over a few months.
Shred first, layer browns and greens alternately, water each layer, then turn on a schedule.
Shredding the plant matter shortens the path to humus: smaller pieces give bacteria and fungi more surface to work on. Add water as you build so no layer dries out before the next one lands.
Alternate brown layers of woody, carbon-rich material with green layers of nitrogen-rich scraps. The stack should hold enough moisture for microbial activity while still letting air move through the gaps between pieces.
Once the pile stands, active management keeps it working: turn the heap to restore oxygen, check that the core still feels damp, and top up whichever side of the mix has run short.
Greens supply nitrogen, browns supply carbon; the balance between them sets the pile's pace.
Green waste is nitrogen-rich: leaves, grass clippings and food scraps. Brown waste is woody and carbon-rich: stalks, paper and wood chips. Compost itself is the mixture of these ingredients used as plant fertilizer and to improve the soil's physical, chemical and biological properties.
The ratio between the two groups decides whether the pile heats up or stalls. Composting runs most efficiently near 25 parts carbon to 1 part nitrogen, and rapid composting is favoured at about 30 carbon units or less.
The table below lists common household inputs with their approximate carbon-to-nitrogen standing, so a scoop of each can be judged against the 25:1 target rather than guessed at.
Keep the core in the 54-71 C band with a wrung-out moisture level until the material is broken down.
The air/water balance is critical: too dry and the bacteria stall, too wet and air cannot reach the core. When the balance is right, aerobic bacteria and fungi convert the inputs into heat, carbon dioxide and ammonium ions, and the pile sits in the 130-160 F (54-71 C) range.
Fungi, earthworms and other detritivores follow behind, further breaking up the organic material once the hot phase has done its share. The whole run to humus takes months.
Symptoms map directly onto fixes: a cool, dry pile needs water or greens; a hot, sour pile needs turning and browns. The symptom table on this site reads those signals against the working band.
The air/water balance is critical to maintaining high temperatures of 130-160 F (54-71 C) until the materials are broken down.
| Material | Green or brown | Carbon-to-nitrogen standing | Notes |
|---|---|---|---|
| Grass clippings | Green | Nitrogen-rich | Adds nitrogen quickly; mix with browns to avoid matting. |
| Fresh leaves | Green | Nitrogen-rich | Part of the green waste group alongside grass and food scraps. |
| Food scraps | Green | Nitrogen-rich | Compostable material; about 20% of landfill waste is of this kind. |
| Dry stalks | Brown | Carbon-rich | Woody material that keeps air gaps open in the stack. |
| Shredded paper | Brown | Carbon-rich | Carbon-rich brown; shred first to shorten the run to humus. |
| Wood chips | Brown | Carbon-rich | Slow to break down; use as a brown layer, not the whole pile. |
| Mixed pile target | Both | About 25:1 | Composting is most efficient near this ratio; ceiling for rapid runs is about 30. |
| Nitrogen-starved pile | Brown-heavy | Above 30 | Above 30 carbon units the substrate is nitrogen starved and the run slows. |
Turn when the core cools below the working band, when the material mats down, or on a regular four-to-seven day cycle during the hot phase.
Turning re-introduces oxygen, which aerobic bacteria need to keep producing heat. It also moves cooler outer material into the core so the whole volume gets the same treatment.
Active management of the pile, such as turning over the compost heap, is needed to maintain sufficient oxygen and the right moisture level. Skipping turns is the most common reason a pile sits cold for weeks.
After a turn the core typically reheats within a few days; if it does not, the mix is off — either short of nitrogen or short of water.
Cold, wet, sour or stalled piles each have a single dominant cause and a single first fix.
A cold pile is almost always short of nitrogen, short of moisture, or starved of air from a lack of turning. A wet pile that will not heat has usually been fed too many greens without enough browns to soak up the moisture.
Anaerobic conditions are the fallback when oxygen runs out: in landfills, where those conditions prevail, food and other compostable materials make up about 20 percent of waste and take longer to biodegrade. The same stall happens in a home heap that is never turned.
The fix order is consistent: restore air by turning, restore balance by adding the missing side of the mix, restore moisture, then wait for the core to re-enter the working band.
Wikipedia, Compost (fetched 2026-10-22) — the source for the ratio, temperature band, turning and decomposition facts used throughout.