Yesterday there was a local news story here about some nearby schoolsâ€™ playgrounds being closed due to concerns about spontaneous combustion from â€œmanufactured wood chipsâ€ that cover those areas. A security camera showed this stuff catching fire. (I assume this has to do with the fact that our temperatures this week are around the 104-degree mark.) Of course, the manufacturers say this is hogwash, but the firemen said theyâ€™ve been worried about this for some time. Have you heard anything about a problem with this product?
Anyway, during the story, they mentioned that compost piles can have the same problem if the compost isnâ€™t turned. Is this true? Iâ€™ve inherited a house that came with a nice compost pile, but I havenâ€™t turned it in the year since Iâ€™ve lived here.
I found this story, most likely the one Candance is talking about. So can a big pile of mulch and compost catch fire. You bet they can. And if they do, and the pile is big enough, it can be a big mess.
So how does of bunch of weeds, grass clippings, and table scraps suddenly catch fire? Before we get to that lets talk a bit about how composting works. Composting is the practice of speeding up the process of creating soil. In your average forest when leaves and branches and whatever fall to the forest floor a whole host of organisms big and small (worms, bacteria, insects, fungus, small mammals, birds etc) go to town, each one breaking down the plant matter until it becomes soil. Good soil is in essence good shit.
In a compost pile you are collecting large amounts of organic matter you want broken down into soil. One of the hardest workers in a compost pile is the lowly bacteria. They do most of the breaking down. To aid in this process you give the bacteria what they need most, oxygen and water. You give it water with a hose, and oxygen by turning it with a pitch fork every couple of days.
So how does this serene process result in a conflagration? Well as these little bacteria are going to town on the leaves and eggshells and whatever else you put in there they create heat (as most living things do when they move around). This heat can lead to the “smoking” you see over the compost pile early in the morning when the air is cool. This is not fire, it is just hot moist air condensing in the cool morning air.
If you have a large enough pile, and you fail to water it and turn it this is what happens. The outer layers of the pile begin to dry out, as more and more moisture escapes from these layers the bacteria stop working as hard, but deep in the core, where there is still plenty of water the bacteria are still going to town. The outer layer now acts as insulation, drying out but also keeping heat in the core. If you are unlucky, the outer layer can get so hot, and so dry that Blamo! compost fire. If you are wondering organic matter most often starts to be in danger of catching on fire when it reaches temperatures of around 300 degrees Fahrenheit. A simple candy thermometer or meat thermometer will let you know how high your compost is “cooking” at.
While the danger of fire is real, don’t get rid of that compost pile just yet. It is very easy to avoid a compost fire.
First, keep your pile small, if you have a lot to compost, make several small piles.
Second, turn and water your pile regularly, if your pile is moist (but not soggy) it will not catch on fire.
Third, during very hot parts of the year pay more attention to your compost pile.
These three simple steps will keep your compost pile producing rich soil, instead of ash.