I once put what I thought were mostly cold ashes on the leaf-compost pile on a very, very foggy evening. The type of fog where headlights at forty feet are just dots.

I walked out to the garage and noticed an orange glow in the garden, all the drys leaves on top were burned up and it was the glowing coals of what was left on top of the wet bottom.

It's so hot, my compost pile is whistling at the dogs. :-p

Yes, many various items can spontaneously combust, but a properly maintained, moist compost pile that is within the size recommendations for home composting (1-2 cubic yards) is not one of them.

The bigger the pile, the hotter they can get. If you have a commercial compost facility or a farm with a huge pile the size of a small building, then you would need to be more concerned about combustion. Otherwise it's nothing but an urban legend.

I think it is rare at the very least for a home compost pile to spontaneously combust. I personally called in a smoldering mountain of mulch once, though, while dropping off yard waste at a public mulch site. Given the conditions I suspect it was spontaneous. The firemen said it had happened before.

I've seen a round hay bale combust in the field across the street. It was not nearly as exciting as the word "combust" suggests, but getting to meet the local fire fighters was fun.

A round bale is probably bigger than most home compost systems, but is it smaller than a building and it's smaller than the piles I make!

Here's my interesting factoid of the night. (Well interesting is relative...) Some farmers with rows of round bales will stick a long piece of rebar through the center of each bale and all down the row of bales have these rebar lengths sticking out. Then is it some poor guys daily chore to simply walk down the row touching the end of each rebar. A hot piece of rebar gives him time to move the offending bale away from the others so as to not lose a whole crop of hay if one combusts. Cool trick.

So seriously, are there really people who don't "believe" in spontaneous combustion?

Hey wait a minute. Are you saying the sun doesn't move around the Earth? :-o

Of course with a high temp of 108F expected, I'm not going to measure the pile today. My 'hot' piles are either in the sprig or the fall, when leaves and fresh grass are available.

PS Of course the earth is flat...

Lloyd

Various items, organic and not, can certainly combust on their own. Very large compost piles can combust. But no one here has presented an example of a home-sized, maintained compost pile spontaneously igniting, and I have never seen that documented anywhere else, either. The maximum temperature of such a pile is approximately 165F, which is several hundred degrees below the temp needed to ignite damp yard waste materials, so it is physically impossible. Hay stacks, oily rags, bags of fertilizer, piles of debris, gasoline and other random things that are not compost piles are not relevant to a discussion of home compost piles.

A properly maintained compost pile is damp and damp materials just don't ignite that easily. And if a compost pile isn't damp, it won't heat up. A dry compost pile could burn, but it would have to be lit by an outside source because it won't be generating much, if any, heat. That is not what is meant by a properly maintained compost pile.

Just because X and Y are similar doesn't mean X will do everything that Y does.

I tend base my beliefs on relevant proof; it's the scientist in me. Like any good scientist, I am open to changing my mind, but only with a sound reason to do so. I'll gladly believe a home compost pile can spontaneously combust when I read a report of it documented, preferably in a controlled setting and replicable. Sorry, anecdotes or approximations will not do. I prefer to live in a world of science, facts, and reality but plenty of people do not. So don't let me spoil your fun. If you want to change the topic or stubbornly believe in folk tales or your own imagination over facts, feel free.

If you think because there is steam in your compost bin it might catch on fire I don't even know where to begin to address that. Are you also afraid that your cup of coffee might start a fire? Just get a soil thermometer and let me know if your compost ever gets above 165F.

This topic has been discussed repeatedly on this forum. Frankly, in the absence of any new evidence, I don't see any point in going over it all again.

That is from the link that kimmsr provided, above.

For what it is worth, hay that has been put up without properly drying out is hay that is more likely to combust. Dampness IS the culprit and a trigger in spontaneous combusting hay. So you might want to think twice becore you comfort yourself that something won't blow simply because it is damp.

Just because some people come here and might only have weenie sized compost piles doesn't mean there aren't some here with bigger piles at home that could use the reminder. *cough* *cough*

Arrant nonsense. Bull manure. You don't know what you are talking about.

I can chip the green branches from an apple tree, completely dry, pile the chips into a pile, and make compost hotter than anybody here has ever seen.

Stay tuned. I might just do this on Sunday just to prove the point.

Karchita, you don't know what you're talking about.

Arrant nonsense. Bull manure. You don't know what you are talking about.

I can chip the green branches from an apple tree, completely dry, pile the chips into a pile, and make compost hotter than anybody here has ever seen.

Stay tuned. I might just do this on Sunday just to prove the point.

Karchita, you don't know what you're talking about.

Moisture is absolutely necessary for the heat generating bacteria. As well as an appropriate C:N ratio and some oxygen. Take any of those parameters away and you will not get sustainable organically generated thermophilic heat.

Karchita's post was very accurate. The only thing she might have also mentioned is that it is dry pockets of material within a larger pile that actually begin the actual combustion. The wet stuff won't catch fire, it is the dry materials nearby that actually begin the ignition.

Lloyd

It seems like we're talking semantics here. Karchita said "damp". The dictionary defines 'damp' as slightly wet.

I can take un-wetted green branches and make a pile of decomposing organic material that will likely be over 170 degrees in less than 36 hours. Just ramial chipped wood.

Paul

Lloyd

:-)

Larger wood chips and not more than fifteen percent pine as more kill the green slime that digests the chips.

Good for up to two years. (Also used for hot water heating.)

As a side note if/when it gets to 180 outside - my compost will provide the cooling effect.

I agree - indoor composting should be banned. Or there goes another for the gene pool.

Anyway, I just don't want you to get in trouble for attempting to make Compost of Mass Destruction.

Sounds like a doozy there, kimmsr.