The guest under "Hot Composting", https://www.helpfulgardener.com/forum/viewtopic.php?t=919, had some good points but, I can't agree that temperatures over 125, 130 F are a bad thing. 150 F to 160 F temperatures (USDA recommendations for hamburger and chicken respectively) are what you need to kill pathogens unless you can sustain the 130 F for days. I can't imagine a hot pile becoming sterile as critters move around and back in as the temperatures first rise and then cool down.
I haven't done any really large composting and I've never seen any reason to concern myself with combustible piles.
For me the hotter the better.
Does anybody else have concerns about getting things too hot?
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Well, there was a fire at the City of Palo Alto compost yard last summer (don't recall exactly when).
It was "spontaneous combustion," according to the City of Palo Alto Fire Dept.
So I'll just continue to be happy with my "medium warm" compost in the BioStack Bin.
This is the first season I've had leaves to add, so I'm hoping for some slightly warmer temps than I've had previously. Previously 110 to 115 deg. F was the max.; maybe I can get *all the way up to* 125 or 130?
Cynthia H.
Sunset Zone 17, USDA Zone 9
It was "spontaneous combustion," according to the City of Palo Alto Fire Dept.
So I'll just continue to be happy with my "medium warm" compost in the BioStack Bin.
This is the first season I've had leaves to add, so I'm hoping for some slightly warmer temps than I've had previously. Previously 110 to 115 deg. F was the max.; maybe I can get *all the way up to* 125 or 130?
Cynthia H.
Sunset Zone 17, USDA Zone 9
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I've heard of spontaneous combustion in compost piles before. I'm sure it does happen in large operations even though there are people who will tell you that it doesn't happen.
I suppose if one's compost catches fire it would become largely sterile but I can't see temperatures higher than 130 F sterilizing compost because the high temperatures are going to be localized to the center and cooling as you move outward. Then once things cool off after peak temperatures, microbes will move back in. Further, there is a whole class of bacteria, thermo something or other, that thrive in those higher temperatures and help produce those temperatures.
I'm not sure what could be the problem with high temperatures above 130 F but far less than combustion.
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I've heard of spontaneous combustion in compost piles before. I'm sure it does happen in large operations even though there are people who will tell you that it doesn't happen.
I suppose if one's compost catches fire it would become largely sterile but I can't see temperatures higher than 130 F sterilizing compost because the high temperatures are going to be localized to the center and cooling as you move outward. Then once things cool off after peak temperatures, microbes will move back in. Further, there is a whole class of bacteria, thermo something or other, that thrive in those higher temperatures and help produce those temperatures.
I'm not sure what could be the problem with high temperatures above 130 F but far less than combustion.
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There are always people trying to make gardening more complex than it is. When I use HM in my compost the center will reach 170 DEG f in about 36 hours. I only wish the entire pile including the outside surfaces would reach 170 Deg. to kill all the weed seeds. As soon as that material touches the soil, it is repopulated with the good and the bad micros. If you are concerned, nothing beats good hygiene.
John
John
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Yeah I gotta remember to keep it simple.
I just remember people bragging about how hot their piles get and then I saw that guest post warning that it shouldn't get too hot. Kind of bugged me I guess.
Well at my scale, 17 cu ft per bin, I don't think I have anything to worry about. I don't think my piles will go sterile or burst into flames. I have yet to see ash.
The best temperature I ever got was 160 F for a short period of time.
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Yeah I gotta remember to keep it simple.
I just remember people bragging about how hot their piles get and then I saw that guest post warning that it shouldn't get too hot. Kind of bugged me I guess.
Well at my scale, 17 cu ft per bin, I don't think I have anything to worry about. I don't think my piles will go sterile or burst into flames. I have yet to see ash.
The best temperature I ever got was 160 F for a short period of time.
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I'm just repeating here what I posted under "Ash in Compost" elsewhere in the Compost Forum.
The City of Palo Alto (California) compost operation experienced a spontaneous-combustion fire on July 23, 2008. The fire erupted approx. 5:15 in the afternoon, full daylight at that time of year (local sunset is approx. 8:30 to 8:45 p.m.).
The San Francisco Chronicle's on-line story about the fire is at:
https://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/07/23/BA1311UPN6.DTL&tsp=1
Cynthia
The City of Palo Alto (California) compost operation experienced a spontaneous-combustion fire on July 23, 2008. The fire erupted approx. 5:15 in the afternoon, full daylight at that time of year (local sunset is approx. 8:30 to 8:45 p.m.).
The San Francisco Chronicle's on-line story about the fire is at:
https://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/07/23/BA1311UPN6.DTL&tsp=1
Cynthia
Personally, I think it was the gnomes they smoke pipes you know. 
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Well I know the mushroom farm by the freeway was smoldering for a couple of weeks and that was the highlight of my morning commute then.
70 C (158 F) kills anything living in your hamburger and whatever your dog left in the yard. 75 C (167 F) kills anything in your chicken and whatever the cat left in the box.
Water boils at 100 C (212 F) so yeah if you're getting that your compost is sterile for a little while. Once things cool down some the microbes will return and the rotting will continue.
The fires occur in huge piles in industrial facilities. I don't see it as a problem in the backyard bin.
I always worry what those gnomes are smoking in their pipes though.
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Well I know the mushroom farm by the freeway was smoldering for a couple of weeks and that was the highlight of my morning commute then.
70 C (158 F) kills anything living in your hamburger and whatever your dog left in the yard. 75 C (167 F) kills anything in your chicken and whatever the cat left in the box.
Water boils at 100 C (212 F) so yeah if you're getting that your compost is sterile for a little while. Once things cool down some the microbes will return and the rotting will continue.
The fires occur in huge piles in industrial facilities. I don't see it as a problem in the backyard bin.
I always worry what those gnomes are smoking in their pipes though.
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Not all microbes are created equal. Those adapted to hotsprings live nicely at near boiling, and those in deep sea vents can live at above 100C (the pressure raises the boiling point). Hot compost is full of thermophylic species that do well at temps that inactivate the species found in cool compost piles. For home composting it doesn't really matter because we are usually not on a time schedule to get the fastest production possible. I need my compost by spring, and because of cold weather I couldn't get it to over heat before then short of setting it on fire. In summer it doesn't matter because I turn it a couple of times times so if the center does sterilize itself itself that material will be remixed anyways.
Somebody posted data on one of the forums that indicated you needed a huge pile of compost/wet hay bales etc to get close to spontaneous combustion, something like a 20 ft pile in an enclosed area,... usually found only at large composting facilities.
Warm to hot compost piles will spew out copious amounts of water vapor, which condenses into steam, especially in the morning when temps are relatively low. The morning light angle highlights them so people think their piles are smoking, and the spores from fungal break down look like ash. The lignin break down reaction deposits black-brown humic products on the fungal cell walls so you have what may look like charred material in with the ashy gray spores.
Somebody posted data on one of the forums that indicated you needed a huge pile of compost/wet hay bales etc to get close to spontaneous combustion, something like a 20 ft pile in an enclosed area,... usually found only at large composting facilities.
Warm to hot compost piles will spew out copious amounts of water vapor, which condenses into steam, especially in the morning when temps are relatively low. The morning light angle highlights them so people think their piles are smoking, and the spores from fungal break down look like ash. The lignin break down reaction deposits black-brown humic products on the fungal cell walls so you have what may look like charred material in with the ashy gray spores.
Some leaf piles of 2 plus yards have netted me large clumps of white/gray mold? I figure this is the real stuff/leaf mold?
More than a few years ago my dad got an idea to go to the local feed mill and compost corn cobs, lots of corn leaves and dry stalks in this.
We must have brought back more than 20 yards of this stuff(many truck loads in a few weekends)(the mill was glad to see it go, it was on the third floor and we shoveled out a doorway and it fell 30 feet to the truck and dad scooped what fell on the ground)(we were big gardeners and this was a hot sticky messy project)(he had 4 willing? strong helpers)(teen boys). It was a big pile. I was the youngest and still liked playing in the pile.
This was placed on top of the old compost pile of 5 plus yards of stuff, well rotted.
That pile burned that year, we put it out several times.
It would smoke and smolder and yes it did catch fire.................. most of the time it was just hot, dad would have us put our hands in it and dig in it just to check out what was going on.
Dad figured out that we had to stop putting it out with water. Somehow the water was part of the problem. So we would spead the smoking charred parts thin over that part of the lawn. It killed the grass.
We would keep the shovels right beside the pile.
But, we didn't turn our piles and dad told us not to, and not to play or dig in it. We had to stay away from it just so it could rest. Somehow digging and playing in the stuff was also part of the problem I was bummed, becaus et was a blast before the law made me stop.
Of course the fire brigade, still had to be on the ready.
He started to use it in the garden, but it killed everything in that part of the garden that year.
The fire portion eventually stopped, but we watched it steam for a long time.
He didn't use it for 3-4 years after that.
YES compost can catch fire...mostly it steams...and it can smoke...and yes flames...believe me.
Do not compost just corn refuse in huge piles.
More than a few years ago my dad got an idea to go to the local feed mill and compost corn cobs, lots of corn leaves and dry stalks in this.
We must have brought back more than 20 yards of this stuff(many truck loads in a few weekends)(the mill was glad to see it go, it was on the third floor and we shoveled out a doorway and it fell 30 feet to the truck and dad scooped what fell on the ground)(we were big gardeners and this was a hot sticky messy project)(he had 4 willing? strong helpers)(teen boys). It was a big pile. I was the youngest and still liked playing in the pile.
This was placed on top of the old compost pile of 5 plus yards of stuff, well rotted.
That pile burned that year, we put it out several times.
It would smoke and smolder and yes it did catch fire.................. most of the time it was just hot, dad would have us put our hands in it and dig in it just to check out what was going on.
Dad figured out that we had to stop putting it out with water. Somehow the water was part of the problem. So we would spead the smoking charred parts thin over that part of the lawn. It killed the grass.
We would keep the shovels right beside the pile.
But, we didn't turn our piles and dad told us not to, and not to play or dig in it. We had to stay away from it just so it could rest. Somehow digging and playing in the stuff was also part of the problem I was bummed, becaus et was a blast before the law made me stop.
Of course the fire brigade, still had to be on the ready.
He started to use it in the garden, but it killed everything in that part of the garden that year.
The fire portion eventually stopped, but we watched it steam for a long time.
He didn't use it for 3-4 years after that.
YES compost can catch fire...mostly it steams...and it can smoke...and yes flames...believe me.
Do not compost just corn refuse in huge piles.