Mulch Sets House on Fire
What? How can mulch set a house on fire?
When I first read this story in the news paper http://avon-oh.patch.com/articles/mulch-spontaneously-combusts-sets-house-on-fire, I thought to myself, “No way. Mulch, spread out in a flower bed, is not deep enough for it to spontaneously ignite. I realize that any organic material that is moist, piled high and compacted will heat up inside the pile and possibly catch fire due to spontaneous combustion.
Ya know, there are people who live near you that want
to buy plants from you. They really do.
It has long been known that green hay stacked in a barn can heat up and burn down the barn. It’s not unusual for large piles of mulch at saw mills and mulch yards to heat up inside the pile and catch fire. If you’ve worked with mulch you know that the mulch inside of the pile can be so hot that you can’t touch it. But in all of these scenarios the piles are large, damp, and have no air circulation inside the pile.
It’s also not at all unusual for mulch along roadways, driveways, and outside of the entrances to public buildings such as restaurants etc. to catch fire from a flicked cigarette butt. It happens all the time.
But when the fire officials investigating this house fire stated that the mulch in the flower bed of this home caught fire via spontaneous combustion I thought to myself; “That’s impossible! Mulch in a bed is only a few inches thick and there is no way in the world that it could possibly heat up enough to catch fire.” I just knew they were wrong about this.
But I could be wrong about that.
I did some research on spontaneous combustion and it is reported that even though nobody can really explain how or why it can happen, brush fires have been started via spontaneous combustion when things as simple as a grassy field catch fire for no apparent reason and it’s considered spontaneous combustion because there is no other apparent source of ignition. Hmmmmm??????
So . . . even though I still have my doubts about these house fires, I do have a theory or two if in fact these fires that started in the mulch are the result of spontaneous combustion. It was really, really dry for several weeks before these fires started and it was extremely hot that day. The mulch was as dry as dry can be, especially at the surface. Mulch is made up of larger and small pieces, with some strands being almost as thin as human hair. I suppose, just guessing now, that if the sun were to shine intensely, as it does when you hold a magnifying glass in the sun, those really fine strands of mulch could ignite under the intense rays of the sun and that would be enough to ignite the rest of the mulch in the bed.
I honestly don’t know.
But if you are concerned, just don’t let your mulch get that dry in areas where the sun beats down. In this situation it had been really, really dry before those fires started.
This is really scary if true. Usually if you have mulch around your flower beds, don’t you water your flowers, hence the mulch gets wet as well? I’m trying to make sense of this.
I’m from Fl. we have a huge supply of spanish moss. Has anyone used that for mulch around plants, etc? Would that also catch on fire? I have it all around my house, to control weeds, etc.
After reading your article about fires and mulch around the house, I had to think that if the weather was indeed that hot, then you should have been watering your plants often, and the mulch wouldn’t have gotten that dry !! Just saying…
When I was a child and we mowed our large
lawn we always used a catcher for the cuttings. They were then dumped in the back yard near the incinerator. It would get to be a good sized pile. When I would dig in it for lack of some thing better to do , sometimes I would find burnt places. I asked my dad and he said it was caused by spontaneous combustion.
I have seen this once with my own eyes. As I was taking a walk past a business that had mulch in front. It was an extremely hot day and the sun was beating on the mulch. As I walked by I noticed that mulch was smoking and smoldering ready to ignite at any moment and as luck would have it a police officer drove by and I alerted him to call the fire dept. This was just a case of being there at the right time to prevent a possible structure fire. thanks for reading and it can happen because I’ve seen it first hand.
Thanks Bob.
My entire condo is surrounded by mulch beds, mostly in the shade, around a brick building.
Flowers & plants do well there are well tended by staff hires and I keep an eye on them now to the extent of dryness.Thank you.
Thank you so much for the article! I use piles of mulch every year and never thought about it catching fire. I’ll make sure not to let them dry out!
Reflections of the Sun from an adjacent house have been know to melt/distort vinyl siding. I happened to see this in Fine Homebuiding magazine/web. Possible ignition source.
I’ve wondered about gazing balls acting like a magnifying glass to start fires. I love ‘em but just wondered.
I believe that it is quite possible Sometimes people leave a pile of mulch in odd places. When I was a child, we had a hay shed burn down, not because the hay was green, but that Dad stacked it neatly in the shed while it was moist. it was abnout 3 feet high.
Also we have a scrub Turkey, a native bird, in Australia which will happily build its nest wherever it likes. It drags and scratches, leaves and good combustible material for quite a distance. Recently it chose the entrance of the church, in a fairly populated area, to build its nest. Where did it get its material? It scratched all the compost from the gardens, around the Car Park, “sweeping” the material across the concrete park with its feet to the place where it built its home, and did not ask council permission. It also raided some of the shrubs for some green material for its nest, especiallf at the base of the nest.The mound is eventually about 3 feet high. If half builds its nest, lays its egs and then puts the other half over the eggs. It controls the heat on the eggs for hatching by moving some of the mulch aside so the nest can cool down, and when necessary, scratches the mulch back to maintain an even temperature.I wriggled and pushed a galvanised pipe right under the bottom of the pile, left it there and pulled it out quickly. and I could barely touch the pipe because of the heat. That bird is smarter than humans. It harvests “Green Energy” and has done for years before we humans even thought of it!
What an interesting story……I love it. MAybe the bird needs to be an honorary member of council? Thank you for sharing! Blessings,
Seems unlikely with constant rain our mulch should set ground on fire.
I think I’ll go water my mulch.
How do I propagate an Oak Leaf Hydrangea? I have 2 pieces and want to get a start. Thanks
To BJ that asked how to propagate the Oakleaf Hydrangea – just stick it in the ground and water it. I have always done it that way and it has worked just fine!
Here’s a follow up to my post with the actual article.
http://www.finehomebuilding.com/design/qa/melted-vinyl-siding.aspx
Years ago it was thought that as glass bottles were thrown out along the road side the sun shining through them worked as magnifying glass and caused a fire.
Mike– I find your arguments to be sound. Properly mulched, and area should never be more than 2.5 inches deep in mulch. I do belive, though, that the landscapers, for profit sake, constantly add new mulch and could, in some cases, get it pretty darn thick. The cigarette butt is more likely the cause.
In our case, a cigarette butt was not the case. After our incident, I was compelled to do research. Yes, there can be spontaneous combustion when conditions are right – dry mulch, dry spell, sunny conditions, and wind. We had a very windy day, and the worst case scenario happened. We were in no way responsible, and it was confirmed by the fire dept and insurance investigation. Bottom line – keep your mulch from getting too dry.
I like your theory about the magnifying glass. I wonder if a drop of dew could act as a lens despite being water?
When I was doing firefighting work one of the runs I went on was a nice warm sunday afternoon where a brand new deck had caught fire. In that case they had just built the deck the day before and oiled it with linsead oil. When they were done they wadded up the rags and put things in a pile under the deck to finish cleaning up later. By sunday afternoon the sun had warmed things up and lit the pile of rags and wood scraps on fire burning down the whole deck.
Organic based fires are certainly possible as nearly every year we have haystack fires where the hay is put up wet enought to break down organically yet dry enough on the outside to compust.
Now something else interesting is that Cold Hardy Palm growes in areas like Z6 and 7 will actually use the heat generated by mulch to help heat their palm tree “cold-frames”, greenhouses and roots of palms like Needle Palms and Chinese Windmills.
thanks, this is great info, i will be sure to water all esp against the house
All I can say is: Thanks for the warning! There are a few smokers in my life, who sometimes arrive in “distracted” mode, whom I can imagine throwing their lit cigarette into the mulch… So, again, I say: Thanks for the warning! I think I will start mulching those areas that have the least “visitor” traffic!
Could be many things, sunlight through glass, if it is shaped right, acts as a magnifying glass, combined with the tiny pieces you mentioned could start a fire. This would not be something I would worry about
However, hay that has been baled before being completely dry – it has to have SOME moisture – can and will smolder upon being baled and eventually start a fire. Those condiions have burnt down many a barn! Ours almost included – we found the bale as it was creating smoke and ashes!
That said, I believe a completely dry layer of mulch wouldn’t be able to combust. A very thick layer, having been rained on a lot, then having a dry spell, it might happen.. just sayin’.
… hay is generally baled in the heat of the day, and that is where the initial heat comes from.
while this is a California publication, with little summer rain… you might find this recent publication of interest
http://firecenter.berkeley.edu/node/65
on “Combustibility of Landscape Mulches”
CHEERS
well dry multch proably will not self ignight. but it is wet mulch that then as every thing starts to dry the sun can heat the wet mulch and there can be a spot between the wet area and the really dry area that gets hot as the decompeing goes on that would be where the spontanious combustion talkes place. In hay barns it is the wet hay that starts the fire and the dry hay supports the fire and the barn burns down. I beleive it is the combination of the two. I agree that 2 to three inches should be enought to keep it moist and not think enought to start fires. fred
i wouild think that bugs spitting up on side of the house and termites would be more of a consern for homeowners. in new your my son runs a landscape business and there was a bug that was ejecting or spitting on the side of the houses. removed multch and problem went away.
I Fred, I run a lawn care company and would blaim this one on shotgun fungus. It grows very well in bark and can be easily destroyed by turning the mulch. It is a great revenue generator for your son. Some pictures on a flyer sent to existing customers works great.
I wonder if there was something shinny that may have reflecked the suns light like a magnifier in the flowerbed? Glass or a shinny can could do that. Even a jar tree.
Here’s another theory. PERHAPS in a really hot dry season, a rain shower could roll through an area, followed by direct sunlight. The raindrops sitting on top of that mulch could act as thousands of tiny magnifying glasses, causing ignition of the already hot dry mulch, much the same as watering your plants in direct sunlight can burn the leaves. Just a thought.
When I was six and my brother was ten we were smoking the straws of oats in the backyard next to an unmowed hay field when we set our fort on fire. Ny father put out the fire with a hose, so there was not much damage. My brother claimed “spontaneous combultion!” Well, my mother had a way of getting to the bottom of things.
Last Fourth of July, some sixty years later, I set a fire with my yard tractor which took three different fire departments to put out, again with little damage. I was suprised to see how quickly even mowed grass burns when it is dry.
I like mulch too, but remember to set up fire breaks using a non-flammable mulch like pavers on bare dirt occasionally. Think defensible perimeters to your garden plots.
It does happen, several holiday weekends ago, a new, very upscale, 2 story house of friends was destroyed in a fire. That fire was determined to have been caused by one who had attended a party there the day before, had gone out back to smoke, and had tossed a cigarette away that fell onto mulch. There the mulch smouldered for more than 24 hours before breaking into flames which destroyed the home.
Cigarettes do a good job of non-spontaneous combustion of mulch too.
Mike I doubt the sun alone shining on thin wood fibers would ignite. Paper and wood require 451 degrees F for ignition. The sun alone could never cause wood to reach this temperature here on earth. I performed some experaments and even with mulch at 6″ deep I could only reach 180 degrees on a 95 degree day. I think a cigarette may very well be the smoking gun, No pun intended! Thank you for your great forum.
I would like to first comment on what Scott Warren said: “No, Scott. Mike said that there was an investigation. Maybe I’m making an assumption here, but presume the investigation was done by professional fire-fighters. It would not be likely to have been started by a discarded, still-lit cigarette because that would have been one of the (if not THE) first explanations that the investigators would have looked for.” So, Mike, I find your explanation extremely plausible (and impressive deductive work, by the way!) and the most plausible cause for the fires. I also want to thank you, Mike. I enjoy and learn so much from your informative emails. Keep up the good work!
At proper depth, I have never heard of mulch spontaneously igniting, but as Scott Warren said, sometimes it is installed much more deeply. “Volcano mulching” around trees is still a common practice, and I once visited a new client who had mulch 4′ deep around a group of oak trees – he had had a tractor trailor dump it out and workers spread it around so that I could not dig deeply enoughto find the original ground surface. It was of course a great expense to remove all that mulch, much more costly than it was to install it to begin with because it was time consuming.
When I was a new gardener, I used cedar mulch on all my flower beds, including the foundation beds. After a few years of adding mulch on top of mulch to get that pretty new mulch look, I learned that my mulch was way too deep, because the cedar mulch does not break down very readily. I had to shovel off 6-8″ or more of cedar mulch. Perhaps at that thickness it could spontaneously combust? I now prefer dark, hardwood mulch, which composts and amends the soil, thus not retaining its original 2″ thickness. I have also personally experienced a small smoldering fire from a ciagrette when the hot end was knocked off the ciagrette, unbeknown to the smoker, which stayed hot long enough to catch the dry mulch surface on fire.
A couple of years ago there was a huge issue of this locally. Small town, landscaping around a public building mulched with straw.
Fire dept cited it as a fire hazard and ordered the mulch to be removed or they would remove it and send a bill. I could agree with both sides in this instance.
1) Straw, public building, cigarette hazard.
2) It wasn’t that deep and it was kept moist from watering.
As far as I understand it, wood or paper needs to be heated to over 400 degrees before combustion can take place, I dont know about Methane though. Also mulch can smolder for weeks and travel 2-3 foot per day before it actualy flames up. So I would blame it on a cigarette coal or butt.
Living in the Old Cross Black Oak Forrest the annual fall leaf fallout is a major problem, and has caused two fires immediately adjacent to my home. With several species of trees coupled with the heavy pollen fronds the buildup becomes quite thick and very compact. On top of that, the entire area is sand and in many places is over 6 feet deep. Heavy rains constantly bring up sand to the surface covering the leaf buildup making a sub-surface layer of dry and decaying material that becomes combustible and will burn underground and unseen until it reaches an area of open surface where it will then easily flame up and spread. That’s what happened one night after a neighbor burned his leaf piles, then left the embers thinking that they would burn out like they had in prior years. I awoke at 4:00 AM that night, and something told me to look outside, and in doing so I saw the entire forest floor on fire covering about ten acres around my home. Fortunately no trees had caught by that time and between myself and the volunteer fire crew we were able to contain and eventually extinguish it.
This is true. I saw it happen outside of my bank. There were no cigarette butts to start the fire, the mulch just burst into flames. If I hadn’t seen it, I wouldn’t believe it myself.
Mulch is a word covering very many organic compounds, fermentation of some of them could fire up quite easy.
Many dumps sell “mulch” which may contain all sorts of things, even broken glass, which can act to magnify sunlight.
It would be interesting to determine the source and composition of the mulkch in question.
In Montana when the days were hot. Clear glass jugs of water would start fires. We were careful to wrap them in burlap or keep them in the shade. Could there have been some such object near the mulch?
Total hogwash & poppycock!
More to ban, license, control and regulate.
Enough of this junk science!
Wait till it happens to you! You’ll be a believer then!
I was in volunteer fire department. I’ve seen a few barns burned down and several hay meadows burned from people bailing hay before it was dry. Even though the mulch was extremely dry at the surface, there could of been some green stuff below that still had moisture and was building up heat and ignited the rest. I’m not saying thats what happened. It is a possibility.
Like MAP said “It would be interesting to determine the source and composition of the mulch in question.”
mike i dont have a comment about the mulch but would like to ask , “i have an oak tree just outside my window, I need to trim it down its about 20 ft tall. will it kill it in this weather. also what about peach trees that is overgrown
I think it can happen if it dry enough and hot enough,just like whiskey and driving very hot and very dry jut don’t mix. mike can I cut the bark off of a red maple branch and use a plastic bag full of dirt around it it make it root,i was going to try it.thank you for your wonderful emails Herb Granger Of Hatfield Pa.
Not sure of mulch, but having taken care of horses and seen of barn fires.
The spontneous cumbustion of bails of damp hay have been studied and found to be caused by the mold growing inside the hay. Wet hay means mold, mold is a living organism that gives off body heat and gaseous waist. Flamable gas + heat = small flame – becomes big flame.
15 years ago I herd about mulch cumbusting, including 1 homeowner who caught it before the fire left the confines of the garden.
The mulch being up aganst the house i would think the color would effect things.
With all the negative problems (mushrooms fugus rotting hide the termites causes crown rot steals nitrogen from the plants, and add fire) I wonder why people still use it. It has been proven that 2 inches of well composted yard waist controls weeds as well as wood mulch, but has a lot af benafits.
But do to regulation in the USA wood trimmings are now impossable to dispose of, and a market for it had to be developed. So we now pay someone to let us have their trash.
Now if you really want to look at some bad stuff look at the ground up rubber tires, The rubber in tires are so hazardous they now recomend you put gloves on before changing a flat! You really want your kids playing in that?
Greetings from Australia. If you can’t get a credible explanation Mike, stick with your gut feeling. Thin layers of mulch don’t spontaneously combust. If you used the same arguments as instantaneous combustion, you could quite easily “prove” aliens.
I agree with MAP. Make sure you know what you are purchasing. I saw a mulch made out of rubber at the same garden shop where I purchased the wood chip mulch.
Funny we just had a small fire that may have been caused by sun and bark mulch with chicken
manure! Yes even the fire fighters were surprised when they searched high and low for clues, we really don’t know for sure.
I’ve never had a problem with “hot mulch” and I also do not thicken it over 1-2 inches. Course, I put mine basically in the shaded areas to keep the neighbors ground covers out of out yard with weed barrier underneath on top of newspapers!
Last year there were two mulch fires in our area. One at Arby’s fast food, another at a friends house. Friend’s mulch fire melted the vinyl siding. Happened just a few days after the mulch was installed.
Hey Mike: I’ve been a subscriber for a couple of years because I like your style, and especially the circa 1995-style email. Was quite surprised to see the upgrade to a WordPress site. Great job, as now people can interact with you and others. No, I don’t grow plants, but I guess I probobaly should — after all this time reading your newsletter.
Frances, it took me a long time to learn to appreciate word press. You can thank my son Duston for the word press sites. He builds themn I try and use them. Thanks for hangin with me for so long!
I work at a Garden Center. We have had customers and people we know put mulch on top of their leaves and catch on fire. This could be what happened here.
I have heard that spontaneous combustion
happens often in the mountain forests of
Montana. They have frequent fires out there
in areas where no one is present to throw
away cigarettes. It must be something for
consideration. Close and constant monitoring of the mulch pile is a must if it is close to
the house.
Funny you should mention this. Last week I was visiting a UStore It facility and as I punched in the code to leave I noticed there was smoke coming from the mulch. There didn’t appear to be anything there, but the smoke got stonger and I could then hear crackles as small flames emerged. I reported it to the office and they took care of it. Spontaneous Combustion???
Near a gate I’d almost bet there is a burnt cigarette butt that started it.
People throw bottles around & other glass things ,it only takes a very small piece of glass & hot sun to set fire to mulch.I’ve seen it in Miami ,over & over.Most people don’t even notice the glass.So it looks spontaneous.Also some mulches have chemicals added that are known to ignite with little provacation.You should only use real wood as mulch .STOP using all the chemicals & poisons, Please!!Wake up America!
The main purpose of mulching is to preserve moisture…if this is your (being a gardener/farmer) objective why you put mulch on your plants near your house or any establishment I think you should not allow these mulch material be dried-up that could invite combustion…Accidental burning? Yes, on big plantation because of impossibility regular irrigation/watering.
I had a fire next to the South side of the house. I had been gone most of the day of the fire. I carelessly left a glass garden globe on a stand close to the ground on top of the mulched bed. It was a scorcher of a day and when I arrived home, I wanted to show my son the new fencing I had placed around the flower bed on that side of the house. I couldn’t believe that the fencing was gone; it had melted and also melted the vinyl siding on the house around 3 feet up the wall. I was one lucky gal to not have the house catch fire. Never again.
http://www.dof.virginia.gov/fire/mulch-fires.htm
I guess anything is possible and so much is unexplainable–but I’ve had mulch around my house for years and even in hottest summer and extremely dry, I’ve never thought it an issue. Other than the cigarette toss, it doesn’t seem like much of a threat. Another threat though that I am hearing alot about is that putting mulch next to your home increases the possibility of termites. This is something I’d like more info about, particularly if the mulch is “treated.” I thought this was the safeguard against termites, but maybe when it is wet repeatedly by watering and rain, the treatment washes away and it does become a termite “treat.”
Thanks, thanks, thanks…for the “Mulch Burning Down a Home….”article. I forgot about this being able to happen and had piled up grass clippings, branches, etc. against my wood fence…I got it out of there post haste… thanks…saved me from disaster!
Brenda
Another cautionary story regarding mulch. I have some in-ground landscape lighting. I covered one of my fixtures with mulch and forgot to rake the area out. That night, the heat of the light caught the mulch on fire. Luckily I discovered it before it damaged the house. Of course the light fixture was a total loss.
In our area, SMOKERS start fires. Recently a young man threw his butt into the mulch, it smoldered for hours and then the house went up in the middle of the night…
Killed 4 family members (except the smoker) and totaled house. SAD!
Mike Here’s a trick I use to propagate woodies and such as mallows. I use bigger cuttings and put them in a 4 inch pot with sterile mix. For the cover, I use the clear, plastic, deli containers that you get slaw, potato salad in. They fit quite snugly over a 4 inch pot. You need to use the ones that hold 2 pounds of deli salad so you have enough room “overhead”. Works great, all parts reusable, the tops last for years.
Adding to my post. The reason for the bigger cuttings is that they will make a saleable 1 gallon next spring if potted in the 1 gallon this fall. Saves an entire year of growing on. My customers are high end Nurseries and demand BIG 1 gallon plants. Also, if the 1 gallons in the spring are transplanted to 2 gallons, by fall you have a plant that can retail for 12-15 dollars, or wholesale for $7.
This happened to my brother-in-law. We figured it was the sun beating on the window, reflecting onto the mulch. Luckily he was home at the time!
Beth, if you can not click the links in my newsletter that’s because you have your Email set to not allow html newsletters. You have to change your Email settings because the html newsletters work the best for most people. I also send in plain text when I can, but I don’t always have that kind of time.
photo of a house fire caused by mulch. detected at 3 am. no sun or reflective surfaces.
http://www.cbc.ca/news/canada/new-brunswick/story/2012/09/09/nb-quispamsis-house-fire.html
If my farmer dad ever had to put hay in the barn that got wet we layered salt between the bales. The salt kept the bales from heating up enough to catch fire.
Most mulch fires are started by someone throwing a cigarette butt in it.
Hi I have tried a product called Fire Chief Coatings it is fire resistant mulch. It really wont light on fire
Check it out at http://www.firechiefcoatings.com