Agriculture Reference
In-Depth Information
Temperature
Compost goes through three stages of temperature that coincide with different microbes.
The easiest way to kill weed seeds and pathogens is to ensure the pile gets up to a certain
temperature for a certain amount of time. If you want to get technical, you can buy a com-
post thermometer and measure the temperature to make sure you're okay, or you can learn
by experience.
Different studies have come up with different ideal temperatures, but it's generally
agreed that 130-150F (55-65C) for several days is adequate. If you're judging with your
hand, it should be too hot in the pile to keep your hand there for long. We don't want it to
go above 150F because that degrades humus and humic acid complexes, as well as scaring
off a lot of microbes. Ideally, it would be allowed to finish for six weeks at cooler temperat-
ures. Still, significant reductions in pathogens have happened when the compost pile never
went above 104F (40C). Even a cool compost, if well-made and left to mature, can control
pathogens to safe levels.
To get the higher temperature, the pile should be at least 3 by 3 by 3 feet as a bare min-
imum, and as much as 5 by 5 by 5 feet, although some people even build 10 feet wide. If
you're making a lot more compost, therefore, you can make a row that is 5 feet high by 10
feet wide by whatever length you have room for. At my parents' tree farm, we have a com-
post “windrow” that is probably 50 feet long.
The thermometer can also be used to tell you when to turn the compost, if you're looking
for fast decomposition. Turn it whenever it goes below 104F (40C) or if it gets too hot at
150F (65C).
Compost that gets too hot will lose even more carbon as carbon dioxide than usual, or as
methane if the pile is anaerobic. Nitrogen is lost as ammonia and other compounds, and
sulfur as hydrogen sulfide — one of the highly toxic “sewer gases” that makes a poorly
built compost smell bad. For the most part, the more frequently a pile is turned, the hotter it
tends to get and the hotter it stays, although the most important part of reaching high tem-
peratures is the right amount of moisture, proper pile size, and balanced carbon to nitrogen
ratio. That being said, if the pile stays hot for months and is rather wet, that probably means
it's anaerobic.
