Compost Temperature Guide
A healthy hot compost pile heats itself. Temperature ranges for each composting stage and what they mean for your pile.
Compost temperature stages
| Stage | Temperature | What is happening |
|---|---|---|
| Mesophilic | 68–113 °F (20–45 °C) | Start-up: bacteria break down simple materials |
| Thermophilic | 113–160 °F (45–71 °C) | Hot phase: fast decomposition |
| Pathogen & weed seed kill | 131–145 °F (55–63 °C) | Hold for at least 3 days (15 days in windrows, turned 5 times) |
| Too hot | Above 160 °F (71 °C) | Beneficial microbes die — turn the pile |
| Curing | Near ambient | Compost stabilizes over weeks to months |
Notes
Insert a long-stemmed compost thermometer into the center of the pile. A pile needs about one cubic yard of material, a carbon-to-nitrogen ratio of roughly 30:1 (browns to greens) and the moisture of a wrung-out sponge to heat up. Turn it when the temperature drops below about 110 °F or rises above 160 °F. US EPA guidance requires 131 °F for 3 days in a closed system, or 15 days with turning in windrows, to reduce pathogens.
Frequently asked questions
What temperature should compost be?
A hot pile runs 130–160 °F (55–71 °C).
Why is my compost not heating up?
It is too small, too dry or lacks nitrogen (greens).
What temperature kills weed seeds in compost?
About 131–145 °F held for several days.
Can compost get too hot?
Yes — above about 160 °F, turn the pile to cool it.