Temperature, Moisture and Pile Symptoms

How to read pile temperature against the 54-71 C working band, and what a cold, sodden, sour or stalled pile is telling you.

The working band is 130-160 F (54-71 C). The air/water balance is critical to maintaining those high temperatures until the materials are broken down, so a core reading outside the band points at moisture or air first, not at the ingredients.

Too dry: the bacteria stall and the core cools even though the mix is correct. Fix by watering the stack and turning once so the moisture reaches the middle rather than sitting on the outer layers.

Too wet: water fills the air gaps and the core goes anaerobic. Fix by turning to re-open the structure and adding a brown layer of stalks, paper or wood chips to soak up the excess. In landfills, where anaerobic conditions prevail, food and other compostable materials make up about 20 percent of waste and take longer to biodegrade — the same stall, without a way out.

Nitrogen-starved: the pile sits brown-heavy and never reaches the band. Above 30 carbon units the substrate is nitrogen starved, so add greens — grass clippings, fresh leaves, food scraps — and turn to distribute them.

After any correction, watch the core for a few days. A turn that is followed by reheating means the fix landed; a core that stays flat means the mix is still off on one side. Fungi, earthworms and other detritivores will do the remaining work once the hot phase ends, and the materials break down into humus in a process taking months.

• Core below 54 C and dry to the touch → water, then turn.
• Core below 54 C and correct moisture → add greens, then turn.
• Core wet, sour smell, no heat → turn and add browns.
• Core in band but dropping after each turn → turn more often during the hot phase.

Further reading

• Greens and Browns: the Ratio Table
• Assembling a First Pile, Step by Step