Frequently asked questions about monitoring heat in backyard compost bins. These answers apply to enclosed plastic tumblers and open wire bins fed with kitchen scraps and dry browns.
Official answer: maintain the pile core between 131°F and 140°F (55°C to 60°C) for at least three consecutive days to kill most weed seeds and pathogens. Use a long-stem thermometer pushed into the center of the mass.
Turn the pile when the core drops below 110°F to reintroduce oxygen and restart heating. Add water in small amounts if the mix feels dusty rather than like a wrung-out sponge.
Turn every three to five days while temperatures are rising or holding in the target band. Less frequent turning slows decomposition but still works for casual gardeners who accept longer maturation times.
Record peak temperatures in a notebook so you can compare seasonal performance. Summer batches usually peak higher than winter batches unless the bin is insulated.