What? How can mulch set a house on fire?
When I first read this story in the newspaper, 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 sawmills 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??????
(Click here to see which types of mulch are the best to use.)
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.
My mulch caught fire (yesterday)memorial day..and no one was home. I live in a cul de sac, You would definitely need a reason to be on my property and the yards are adequately spaced apart. My neighbor happened to be pulling up, saw the smoke, grabbed my garden hose and put it out. Bottom line, there was no cigarette butts present and my video from my house does not show a person on my property. I think it was the angle of the sun., dry grass and mulch over 5 days no rain and intense sun rays. Thank god my neighbor pulled up or my 5 year old home would have caught fire. The mulch is not laid thick.. 2 inches or so, however the only difference is my landscaper laid a tarp/fabric on the dirt before he laid the mulch. Now I know to be mindful to wet the mulch down but honestly, I’m going to get rid of it all together.. this was scary!
It is scary and I think you are right. Maybe the intense sun bouncing off a window or something.
I have worked with mulch my entire life. if you put 2 to 3″ down like everyone recommends mulch will not catch on fire. it has to have a catalyst of some kind to start the fire.. I had an 2 acre field where the city brought in there cutting and shredded it in to mulch. They dumped the mulch about 10 feet deep. now that caught on fire. For 5 days. if you get mulch to deep it will start on fire. mulch get very hot inside it.
Mulch is intended to keep the ground around plants/flowers more moist than without mulch. However, any gardner also know you must water mulch just as you water soil around plants/flowers. As soil will dry out, so too will mulch. Mulch is not magic and thus keeps plants/flowers moist with magic but must also be watered just as does the soil. The benefit of mulch is that it will keep soil moist longer than bare soil. We find that too often folks will read some articles regarding gardening but not read it all and thus read “mulch will keep the soil around your plants moist . . . but you must keep reading the entire article where it also states that after watering the mulch, it will keep the soil moist for a longer period that bare soil not covered with mulch. Use thy head folks.
I had an antiques store with huge display windows, and I hung Stained glass pieces in it. Many of them had beveled glass pieces in them and when the sun would hit them just right, they would focus a pin point light on my walls or wood shelves. I must have called the fire department three times because I could smell burning but they never could find anything but a heat signiture in a certain spot. Ten minutes later, that heat signiture would go down significantly. Thank God it never got to the point of ingnitioin, but when you smell that burn’t wood smell, you know it must have been awfully close. Thank goodness, the sun moves, because had that focused light stayed in one place for just a few monents longer I would have been having to use my fire extinguisher!!!! Some people hang glass wind chimes out in the yard and sometimes they have beveled glass in them. The sun at the right angle could focus through that glass and set leaves or mulch, anything dry, on fire.
Vicki,
This makes perfect sense and is the most logical explanation I’ve heard yet.
Better late to the party than never, right?
A true story for ya…
Was over at a friend’s and he uses soiled barn hay as mulch/fertilizer in his garden patch. Puts it down all year long as he takes it out. Even during the winter, laying it on the snow . I was over there one day just after the first day of spring one year and his garden patch was smoking. He said “steam” and nothing to worry about, happens every year about this time. I told him no, that’s smoke. It was indeed smoke. He has a habit of throwing his old woodstove ashes/chunks right out there with the mulch. He swears they’re always cool when he does it…but apparently not. He’s been lucky so far that the snow mixed in with layers of his mulch have always kept the stuff from fully igniting…but I told him he’d better stop or else one these days he’d be a house fire statistic.
This additional comment to my question about the Pampas grass:. I forgot to add that there is a ground-floor sliding glass door on that side, which is often in shade, being somewhat overgrown on that side. Also, the sun shines on the pool water quite a bit. (Sorry for all the typos!, typing this on my phone!)
Mike, I find this subject all rather interesting. I see that this story went out already months ago, but I do have a side question. Hopefully this one hasn’t been answered in the comments already, I haven’t had time to read a little t of them yet.
My question is this:. How much of a fire hazard are Pampas grasses? I’d love to grow them around my pool, but I’m concerned about the risk, since the pool is close to the house. We live in St. Louis,band summers can get really dry and hot. The pool deck does get a decent amount of shade, and there is only one small second-story window on that side. I called our botanical garden, who told me they weren’t sure, but that there could be some risk. Would hosing them down in hot, dry weather help? Thanks for any input you can give.
Kay,
During the growing season grasses are green and not really flammable. Come fall I’d cut them way back. In my mind it’s not that much of a concern but only you can decide. How many others have them in your area? Really, dead leaves are probably far more flammable.
Thanks, Mike! (I’m not aware of any others growing them around here.)
Has anyone considered The Global Warming we have been facing ? Maybe years back it was safe but like he said if. it receivesGail direct heat and dries it will ignite
After reading all these comments, it seems clear that mulch can easily ignite, whether spontaneously of from an external source like a discarded cigarette butt. My take-away is: mulch may ignite. and often does. That being the case I’m re-thinking how I dispose of my chipped wood. Till now I have been spreading wood chips under the pine trees lining my driveway. to keep the weeds down. No weeds and looks pretty good too. But if one of my 100 or so pines caught fire? Yikes! Look out!
I saw a hospital having mulch beside the side walk on fire by a cigarette, I removed the cigarette and used my foot to stop the fire, this is why I do not use mulch near my home having wood, good wisdom.
A similar thing happened to us a few years ago. We were outside when it happened. A small pile of fall leaves about 10 feet from our barn just burst into flames. The pile was maybe a foot deep. It was the beginning of May in Buffalo, not exactly a dry season. My daughter was on the trampoline when she hollered out to me and pointed to it. No one else was around at the time. The fire department came and didn’t seem surprised in the least.
Lisa,
I find this really interesting. I can’t really get my head around it, I’m perplexed by it.
I noticed something on my lawn next to my house house. A spot of light.I went out and found that it was a reflection of the sun off a dual pane thermal window. Let me explain. Alight vacuum is drawn between the two panes and filled with argon or some other less heat conducting gas, this low pressure allows the ambient air to bend the panes in ward (on mine until they touch in the center) creating a convex lens effect, thus focusing the sun light just as a magetfrying glass. Did I say the lawn was hot. The lawn was HOT.
Christian,
Great info that helps us better understand what is happening in these situations.
Lordy don’t believe everything you read .. I have mulched all my gardens. I live next door to a fireman.. Mulch will surpress flames and holds moisture well.
Read this same news article some years ago. Remember that an additional factor was possible reflection/concentration of sun rays by reflecting from sizeable window(s). Checking, centers of reflected sun light was significantly hotter than expected.
Jim,
This makes sense to me. As you know, I’ve got these two donkeys who on a cold sunny day will stand in the direct sunlight. Cold as can be outside but it’s amazing at how much that sun warms their bodies on a cold winter day. Magnify that with some reflect glass and a much warmer day. I have no idea, but it’s all interesting.
Well you are entitled to believe what you want, but I did have a fire in the mulch I spread along south side of my house. It was hot enough to melt the vinyl siding and burn up the mulch. I was away from my home when it happened and I’m thankful that it did not do more damage. So be careful.
Hi Rosemary,
My son has a home in Maryland and his siding on his 3 year old townhouse melted! How could that be? After much research and discussion with vinyl siding people AND window people – it was determined that the townhouse
next door – separated by about 30 feet of lawn – and the type of windows that were installed were the culprit. The angle and reflection of the sun on the windows were directed towards my son’s townhouse.
He had to replace his siding with now $$ input from insurance or community.
He was told to ask his neighbor to change out their windows!!! And this would mediate his problem of melting siding. GO FIGURE!!!!
Why Landscaping Mulch Can Spontaneously Combust—and How to Prevent It
By ANYSSA ROBERTS Updated on 06/05/21
Fact checked by SARAH SCOTT
This article pretty much confirms what I’ve been saying about mulch fires. Most likely caused by another source of ignition like a cigarette butt. I will forever have a difficult time believing that mulch that is even 6″ deep would spontaneously combust. I say that based on over 50 years of crawling around on my hand and knees working in and with mulch. Does mulch in pile get hot? Absolutely it does and I’ve had mulch in piles that were so warm that I could not place my hand in the mulch. But never, ever, have I experienced mulch on the ground even being noticeably warm. I know experts can contradict me, but who is an expert? 50 years of working with mulch, I kinda consider myself an expert. https://www.thespruce.com/why-landscaping-mulch-can-spontaneously-combust-and-how-to-prevent-it-5184551
My house and barn should have been burned down 10x by now. I ve been mulching for decades. Ill risk burning my house down versus pulling all those weeds.
How about lightning strikes causing fire next.
Amen!
I remember stirring up piles of grain to cool them off. They heated up to the point of smoking a bit and too hot to hold in your hand.. This was late fall in N/W Ohio and the grain was not wet and piled on a bone dry wood 2nd story barn floor. No sunshine, no cigarette butts, no reflective material, and yet, that grain got pretty near lighting up. The farmer, my Brother in law, assured me it would light up if we did not cool it down. Some of these posts flatly deny spontaneous combustion. “THERE IS NO SPONTANEOUS COMBUSTION”. Only on the internet do you see stuff like that. OK if there is no such thing as spontaneous combustion then I should be President. Really!
George,
I’ll agree with that, I’ve had my hand in some mulch piles that were just flat out too hot to touch. But mulch laying on the ground only a few inches deep I’m not buying spontaneous combustion for that. I’m not sure what to buy regarding that. Not really convinced these fires did not have an external source.
Yes, we should be critically thinking all the News…
You are right about stirring the grain. I used to work at a bark dust company and the piles of bark dust got so hot that we had to call the fire department a couple of times a year (especially in the summer) to put out fires from spontaneous combustion. It’s definitely a real thing.
Can you send me your recipe for your weed killer? I know it is vinegar, salt and a couple drops of dish soap but I forget the measurements.
Thanks, Anne
Anne,
I need to do an article on that as soon as I can.
Yes indeed you do…salt is fantastic for a driveway or an area without planting but it’s not very good at all for a landscaping bed area. Your vinegar is good as it strips the wax like outer coating of the plant… I use a cup of cheap vegetable oil and a 1/4 cup of dish soap…shake it together first to make the emulsification then and the cup of vinegar in a gallon or two of water in the sprayer… one gallon for the vine type plant and two gallons for your common ground weeds and grass. I’m quite a big fan of the diaquat-diabromide salt… or Reward as it’s a 24 hour burn down and smokes the foliage off… pond safe… I bought the handcart at harbor to pull my 20lb. Propane tank and use my weed dragon…wet the mulch first!!! 😂😂👍. I bet it’s the black dye that actually reacts and causes the fire… like a chemical reaction or something…dyed mulch is not good leaching into the soil year after year in my thinking….mulch better off with an organic product only. Every time we tamper with or try to change nature…. we have problems…, God Bless Everyone!
Mike,
I recently took part of my Bermuda lawn to make a bed for some Japanese maple, crepe myrtles and camellia bushes. I used a generic round-up then waited until it started taking effect, then replaced the clay/rocky soil in the plant holes I dug out with MG garden soil, plus some black kow & potting soil I had on hand.
In addition I did a brick & stone pattern in the middle as I am an artsy type.
Even tho we finally stopped buying 100+ bags of colored mulch every spring and switched to pine bark mulch, I bought some of the colored mulch for the new bed as it was on sale for the holiday @ $2 bag and figured it was cheap way to keep the Bermuda covered and then spray (kill) any grass that peeks thru, esp as it will the 1st summer.
In addition, have several “window boxes” that are designed for deck rails on my deck that I had planted seeds so it mostly is a seed starter mixture. Try to water these at least every other day, realize I should do every day, just frankly forget to do it.
Anyway on the news weather guy said to water down your mulch beds as we have had weeks of 90+ heat w/out any rain and it was fairly windy. So went out and in addition to watering the plants twice a wk wet the mulch around them too.
Fortunately have a sidewalk plus some scalloped pavers in between the hse, but the deck boxes are of course on the deck. We also leave some leaves from previous fall around the hse to help feed the plants (we have planted lots of perennial bushes and Jap Maples but should I blow them out too?)
We live on a wooded lot with lots of mature hardwoods but an arborist told me that we don’t have many tree fires in GA (even during a 6 yr drought we had yrs ago) because we have such high humidity. Yet reading these comments has me wondering if humidity is a friend or foe.
VERY CONFUSED on what precautions we need to take???
So is colored (dyed) mulch the one mostly catching fire? How about nat’l pine bark mulch nuggets? Pine straw? Many folks use pine straw here as a cheaper alternative as it is plenty available, think it may feed plants as it breaks down (only last 1 season tho).
Also wondering, should I be wetting the newer mulch every day, or just when I water the plants, OR should I NOT be watering it at all??? Any advice for the deck rail boxes?
Jan,
Only wet your plants when the plants need water. Too much water can kill your plants. Mulch? I don’t know, it’s not something I worry about because these fires are so random and truly rare. It’s just that they make news when it happens. Part of me still wonders if an external source has ignited this mulch but others say no way.
We live in Eugene OR and our mulch was smoking and on fire in some spots. We happened to notice it before it got out of control. While it was smoldering I dug up the mulch and found the mulch moist two inches down from the surface. The mulch is only a couple inches thick.
Thanks Brandon, interesting facts, might help make this all make sense.
Fter reading many of the stories and comments I am left with 2 questions. 1) is it possible that any moisture in the form of a water droplet would refract the sun long enough to ignite thin plant material? 2) are there any chemicals used in the bags of mulch from Lowes or Home Depot that may reduce the temperature threshold for spontaneous combustion?
Clint,
The droplets of water? I think it could be possible.
Bagged mulch? I don’t really think it’s treated.
About a month or so ago I was at Hobby Lobby and saw flames where there was about an inch or so of black mulch. I ran to my car and got 3 bottles of water to put it out. I told the store manager and he said it wasn’t his problem but he would contact the caretaker of the property. When I went back out to my car.there were 3 more spots on fire flames about 6 inches tall. It had been dry for only a couple days. Its scary to think that my car could go up in flames from parking in a parking lot where there could be a fire.
Shirley,
That’s crazy, thanks for sharing.
We were at a playground a few years back and the kids were swi ging. We noticed smoke and the mulch under their feet was smoking. We moved all around the playground and started turning it over and the entire playground was smoldering. Fire Department has to be called and closed the park. Crazy!
I put a couple of bags of the mulch that was on sale at Lowes, the brown colored stuff, in the fall to fill in a place where I had some erosion. When I looked at my fence in the spring it looked like it was leaning downhill. I went to push on it and it was completely burned through and the mulch was gone. I checked the next three posts and they were all burned through. I have pictures of the burned 2 X 12 and the 4 inch fence posts. So yes mulch only 6 or 8 inched deep will burn.
Peter,
That’s amazing.
Hi Mike,
I enjoyed this mulch fire article as well as your other informative articles and videos. I am a retired Fire MARSHAL and investigated many, many structure fires.. TWO of the fires that I investigated were found to have been caused by the spontaneous combustion of sawdust….and it didn’t take a lot either. No more than a household bucket full.
I mention this because I for one throw the sawdust into my mulch pile, outside and quite some distance from my house. I collect the sawdust from a catch bucket underneath my table saw in my shop ( just like one of the fires I investigated). Ever since then, I empty it regularly nearly after every use. I hope this helps some of your readers and helps to validate it’s dangers,, as well.
Bob B…from NJ
Thanks Bob!
I put some black mulch down about a week ago. Saturday it got very hot and sunny where I had put it down. Mid day I smelled something burning and looked all around the neighbors to see what was burning but saw nothing. That evening my husband asked me what I was burning. I said nothing. He said look out front in the ground cover along our wall where I had put mulch down. It had burned the roots of some of the grass cover and would have burned the house had we not been here. Scared the death out of us. Are the red and brown mulch as bad as the black? There is old black mulch around the house that was put down well over a year ago. Do we need to dig it all out or should it be safe after all this time.?
Sandy,
I’d say the old mulch is fine.
I found this article when doing a search on “combustible” mulch to try and explain what happened to me today. My daughter and were leaving a chain restaurant in Frederick, MD this afternoon. It was over 90 degrees, sunny, and hadn’t rained in 4 days. As I pulled out of our parking space, I noticed smoke coming from the landscaping. I jumped out of our van, expecting to see a cigarette butt in the mulch. There was nothing but dark, smoking mulch. I grabbed a water bottle, doused the area and ran inside to alert the staff. Weirdest thing I ever saw.
Deborah,
I am hearing more and more of reports like these.
Our hay stack caught fire one year due to spontaneous combustion and we were told to make sure the hay was completely dry before baling and to salt down the stack. So be sure to check those mulch piles when it gets hot.
It happened to me about 20 years ago. I cleaned out the bedding hay form sheep & goats in a barn and filled up a manure spreader. As I started to spread the compost, it began to rain hard so I backed the spreader and tractor back into the barn. About a week (maybe it was 2?) later I was back in the barn and the spreader was smoking right in the middle. I stuck a hay fork in it and it burst into flame. I had given it enough oxygen to light it up. I still had the tractor hooked up and pulled it out of the barn and started to spread it, but the agitation of the spreader made the fire worse. I doused the flames with a hose until it was cool and got it out of the spreader, but not before it had burned out the boards on one side and part of the bottom.
If you do, in fact, have scientific evidence that mulch spread out on the ground a few inches can catch fire spontaneously, please post your sources. If you have done your research, that research should be from the experts in the field, including scientific periodicals, professional journals, and so on. I have been investigating fires for almost 30 years, and the process of spontaneous combustion in mulch is a complex reaction that cannot occur in a couple inches of mulch. Those fires are usually ignited by material dropped by people outside, a cigarette, a lit match, a magnifying glasses, sparks or embers, etc. Good luck getting anyone to admit it though.
There has to be another reason. Here are a couple of sources.
#1
http://www.soilandmulchproducernews.com/index.php/frontpage-articles-hidden/160-a-perfect-storm-mulch-fire-dynamics-and-prevention
#2
http://www.fireengineering.com/articles/print/volume-161/issue-3/features/combating-and-preventing-mulch-fires.html
#3
http://www.nfpa.org/news-and-research/publications/nfpa-journal/2011/september-2011/news-and-analysis/fire-analysis-and-research
The reason I am on this site is because I was looking for answers on why the mulch in my flower bed spontaneously ignited on Sunday. We spread new mulch from Lowe’s in the flower beds on Saturday evening. Sunday around 3:30pm, one of the flower beds caught on fire for no apparent reason. It was about 75-80 degrees with full sun beating down. There was no one outside to cause a spark and no one was smoking. Luckily my daughter walked out of the house at just the right time to see the fire. We put it out with the hose but if she had walked out any later who knows what would have happened.
Just talk to firemen in Dallas ,Tx. It happened to us a couple of years ago. The weather was extremely dry and so was the mulch.. We smelled and caught it before it spread to the house, The firefighters said it happens often in this area.
I’m reading this article because my mulch has caught on fire twice this week (just happened 20 minutes ago). We were planning on replacing the mulch–not anymore!
I worked ar BJ’s wholesale for 2 yrs and the stor had to have a portable fire extinguisher. By the front of the store so one of the employees could run out and put out the mulch fire everyday during the warm months CIGARETTES! From shoppers. This is still happening 20 yrs later. Yes we did have ash tray receptacles outside!
Here’s a great summation for us mulch-loving nerds.
http://www.soilandmulchproducernews.com/index.php/frontpage-articles-hidden/160-a-perfect-storm-mulch-fire-dynamics-and-prevention
There are many comments here and i have not read all, so might have been mentioned. Alot of time people do have some type of decorative items in there flower beds, glass chips inside concrete for steps(piece of glass could of came loose and was setting on mulch to give it that magnifying glass effect). Othere wind chimes with glass or crystal, if no wind blowing light could shine threw in 1 spot. You can even start a fire with a water bottle. so might not of been “Spontaneous ” combustion per say but combustion caused by a foreign object reflecting light. I am sure the fire department didnt look for anything like that. Well Mike hope my rambling makes some sense, and ill see you on the boards
Just J’s Lawnscape
With today’s windows all having reflective tints that block uv rays I would suspect a reflection directing rays from these windows, into the mulch, might be the culprit. Google vinyl siding melting from reflections. There is a building in Vegas that is reflecting sunrays to the pool below and it is too hot to sit there!
Years ago when I was visiting friends in London, they had an extremely hot, dry summer and Hampstead Heath — a large grassy area where people could wander the meadows and hardly ever see the city — kept catching fire. They said that pieces of broken glass were acting as lenses for bright sunlight. The drought left a lot of dry grass standing. So, lots of grass fires. And a lot of people volunteering to pick up glass wherever they went to help prevent fires.
I don’t believe in unexplained spontaneous combustion — you just need to look harder to find the cause. Cigarette butts, or a little bit of hot ash carried by the wind, are still the most common cause of fires.
Smelled smoke last night before going to be and thought it must be a neighbor having a fire pit. When we woke up this morning and went out front to sit and enjoy a cup of coffee we were greeted by smoke coming from the mulch bed. The area was approximately 10′ x 3′ and it was clearly smoldering. No cigarette were present nor were any smoked in the area. No electrical plugs in the area. Thanks for your post as it may have solved a little mystery for us. Thank God it didn’t catch the house while we slept.
I am reading about mulch and spontaneous combustion because earlier this afternoon I was lying on the couch dozing off when I was awakened by the smell of smoke; in fact the house was starting to fill with smoke from outside. There was so much smoke I couldn’t even see the back fence. I called the fire department and ran outside to find a flowerbed in flames 2 doors down. My neighbor put out the fire with a garden hose so luckily his house was fine. The fireman said last year 4 houses in our area burned down due to mulch fires (I remember seeing two of them after the fact).
I asked the fireman about the spontaneous combustion but he said probably not; each of the house fires started when someone had thrown a cigarette into a planter or flowerbed. Upon closer examination we found a few cigarette butts close to my neighbor`s charred flowerbed.
Either way I don`t think I want something this highly combustible next to my house. I`ve found enough cigarette butts on my lawn lately (we are non-smokers) but I don`t know who the moron throwing them is. I am going to ask the landscapers to remove this crap.
I work in the paint & coatings industry. We’ve had dozens of spontaneous combustion fires over the years. Alkyd resins (from linseed, soybeans) and limonene from citrus used in stains and varnishes produce more fires than you would imagine.
I had loaded a spreader with cow manure when it started to rain. I pulled the spreader into the barn to try to keep it dry. About a week later I noticed smoke coming out of the barn. I went to the manure spreader and couldn’t keep my hand over the top because it was so hot. When I pulled it out of the barn with the tractor, the jostling was enough to start it into flame. It burned through about 1/2 the wood in the spreader before I could extinguish it with the hose.
Cliff,
That’s amazing but not surprising. Thank you for sharing your experiences with spontaneous combustion fires.
The fireman told our kids that the window box outside the kitchen was the cause of their kitchen fire. This was in the winter and the box was just full of dirt and whatever small amount of potting soil had been used to plant herbs in the summer. Hard to believe but the only explanation for the way it started!
The fires are usually caused by hot sun on broken bits of glass. A broken piece of bottle can act like a lens and concentrate the heat, causing smoldering and fire. That’s how grass fires get started.
There is really no such thing as “spontaneous combustion” — although I agree that sometimes raw compost can get pretty hot. This is why compost should be well rotted or aged before you put it on garden beds.
Has anyone ever heard of sacks of leaves catching fire when the bags are clear plastic? My husband believes they will, as opposed to white or black opaque bags because the clear plastic would act as a magnifying glass, heating the leaves to the point of combustion. I have at least 100 bags of leaves piled around the metal skirting of this old trailer we live in, stacked for insulation through this last bitterly cold winter. Thanks to them, our pipes never froze, but now I need to dump out the leaves and compost them and was wondering if combustion could be a problem as the weather warms if I don’t get them dumped out right away. There is some moisture in all of the bags, but most are still as fluffy as they were when bagged last fall.
Becky,
I’m certainly no expert on this, but I would think that damp leaves would heat up in the bag faster than dry leaves. But your husband’s point might be valid about the sun hitting the bags. I would think the conditions would have to be just right.
if its plastic and its sealed, i would think there wouldnt be enough oxygen in them to support a fire, but i could be wrong
I would be curious to know more details on these fires. Temp of the day, last rain, humidity. . I have seen wet hay in barns get very hot, and have been told it can catch fire. I personally have never seen it happer or anyone who has. If the compost has manure in it its a long known fact it not only ca lawyer catch fire, in closed areas it can explode from methain build up . That is why on sailing ships boxes of manure were labeled S(hip) H(igh) I(n) T(ransit) … i know cats and no doubt other critters will rake mulch over their droppings to cover it. Personally if i had to guess that is the culpret if the fires
Hey Mike,
I was working at one of our local gas stations several years ago and a large mulch truck pulled in with screened sides and back and was hauling several cubic yards of woodchips mulch, nearly fully loaded… As he stopped off of the freeway to fuel up the truck… Several of us around the station saw wisps of white smoke coming from deep in the middle of the loaded truck and becoming thicker and heavier……
The manager of the station came running out and told the driver to not fuel up and to pull away from the pumps and up the road right away, about 75 or 100 yards away and he would call the fire department…By the time the fire crew arrived the fire was more heavily involved…They finally had to call in a back hoe to rake out and remove most all of the load out of the truck on to the ground.to totally get it watered down and put out..Their investigation found it was spontaneous combustion caused, as no other flame sources were found within the mulch…
I quote someone I read some where & I believe the same way if you need mulch you don’t have enough plants, After reading Ossie’s post I really need to get into the attic eves and get rid of that 3 foot bird nest. Dang woodpeckers won’t quit eating my house and out buildings. I was banging on the tub the other day to scare them away from the house and that crazy bird just bent over upside down to look at me in the little window in the shower..
MULCH yes it happened to me I had purchased Mulch from Home Depot and put it in flowerbed along with landscape lights and sure enough the mulch started to smoke and caught fire Luck had it that my Garden Hose was nearby ,,BEWARE they treat their Mulch with some chemical Compound..Now I use crushed Stone as Decorative mulch ….I had Local Fire Dept test it and they agreed it was acompound that is chemically colored Thanks for emails
You said landscape lights, might of been a reflection of light pin pointed on a spot that caused it to heat up and catch fire
Searching for an answer to this question, I found your article. I thought it might be worth noting that I just put out a fire in a flower basket hanging on my porch rail. No power source around and at night, my son witnessed the sparks begin to fly and then the flames followed. He quicKly called me and it took a fire extinguisher to put out the flames and my porch rails will have to be replaced.
The depth of the mulch is only about 6 inches, so that would not be the reason. It is also in a rather shady area, that is why the basket doesn’t have flowers, not enough sun.
We have used mulch for over 17 years and never heard of a problem. I will continue to use it, but I will keep a closer eye out for trouble. This has to be a freak incident, but had we been asleep like normal, it could have been deadly.Very grateful for quick eye and a working extinguisher!!
Kathryn,
Thanks for sharing this. I can’t imagine how a fire could start like that in the shade, at night. But there has to be something that I am missing.
I don’t know off any studies on wood mulch fix but know that it has to be laid thick for it to ignite. There has been studied in hay fires and I know of An empty building that caught on fire from a box of wet rubber gloves in the corner. Ok what has been found to cause the bales of hey and the box of gloves to ignite.
Microbes..The material inside gets wet, the microbes start eating it, they produce heat and methane. Eventually the heat the microbes give of get hot enough to ignite the trapped methane, yea the bus like us fart.
My feeling is that the mulch ignites in the same way.
I have never understood way people use wood mulch with so many negatives. Artillery Fungus blotching the house and cars, robs nitrogen from the ground, requires hours of watering to get through the mulch to get the ground under it wet.
It has been proven that 2 inches of good leaf compost applied once a season will keep the leaves down, and catalyze the garden!
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
Most mulch fires are started by someone throwing a cigarette butt in it.
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.
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
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.
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!
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.
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.
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!
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.
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
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.”
http://www.dof.virginia.gov/fire/mulch-fires.htm
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.
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.
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!
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.
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.
Sounds to me like what i said esrlier. Animal pooh in the mulch. Not to mention it can get really hot there
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.
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!
Mulch comes in many grades, and from many distributers. It would be interesting to see if both mulch fires purchased their mulch from the same resources. I work with mulch every day, spread it in many gardens, in many locations and never had a fire. FYI the colored mulch is nothing but ground up pallets and adds nothing to the soil but will drain it instead. If using it keep it away from homes it will attract termites.
Good tip! People should also be aware that they are adding yet more synthetic (and toxic) chemicals around their homes when using colored mulch. Also, many pallets are chemically treated with poisons.
For termite control – look into beneficial nematodes. These microscopic soil creatures feed on many soil dwelling pests, or the soil dwelling stages of numerous pests – including termites!
Also carpenter ants, fleas, ticks, Japanese beetles… Arbico Organics has loads of info on their website. I am not affiliated with them in any way – but I have used their products and similar ones from other companies to successfully control many pests, especially fleas, in warm humid areas of the US.
It’s a great alternative to putting out yet more poisons, which insects and other pests quickly become resistant to anyway.
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.
Hmm…installed….. So, commercial mulch? I know they sometimes color it. I wonder if it’s treated with something flammable?
In our area, glare from energy-efficient windows has started fires.
Yes, it’s a “thing” – take care:
https://www.probuilder.com/low-e-windows-blamed-fires-north-carolina
and
https://www.wral.com/glare-from-energy-efficient-windows-can-melt-siding-vehicles/13614716/
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!
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 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.
Jode – and that ‘rubber’ mulch isn’t even really rubber. It’s old tires ground up- and they are made of synthetic rubber, which is actually a type of plastic. Like most plastics, this old ground tires (and similar stuff) outgas and/or transfer harmful chemicals through direct contact for decades, maybe longer.
Modern tires are marvels of engineering, and we all appreciate that. Yet these days we are surrounding ourselves in plastic.
For info on why that is not a good thing, put ‘plastic’ into the search window at the Mercola web site. This physician has links to the research to back up the information in every article.
I am not involved with Mercola or the site in any way, but have found it to be as useful for health issues as Mike’s site is for growing plants!
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.
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?
Free public service:
That should read: hay bale; and yard waste.
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.
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 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.”
Hay must be properly cured before it is *baled*. Not only to prevent fires, but also to preserve the nutrients, and prevent the growth of molds and other organisms which can be toxic to the animals that eat it.
Damp hay is very different from shredded or chipped wood, though.
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!
My sisters house burned down the other day due to mulch. We have not had rain for weeks and the temp was 90 and sunny. Mulch fire caught corner of house and crawled straight up to 2nd floor
You can get off your soap box, there was an 3 story apartment building in our town that housed 26 apartments that was totally destroyed. It was recently built and was fully sprinklered and had a state of art smoke alarm system.
The cause was the mulch placed along the south side lwall of the complex that combusted in direct sunlight. It travelled on the ouside of the building ( it was in the back of the building where it was not seen) , and caught the entire roof and attic on fire. Sprinklers and smokes were totally useless until the ceilings started caving in. Thankfully no residents were home on the 3rd floor at the time.
The state fire marshall came in because of the magnitude and it was concluded that the mulch company had used an insecticide treatment chemical on the bark (this has been banned in MA for quite a while now).
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?
This is the most plausable answer and yes, if the mulch caught fire near the house that means the sun could have been reflecting off a window. Mirrors can be use to start fires just like a magnifying glass can. Window with the right material placed behind them can act just like a mirror with reflective capabilities..
My first (carefully layered) compost pile caught fire——I was in Yellowstone Park and returned to fire trucks monitoring for another spark. The pile was in a semi-shaded area. Beginner’s luck 🙂
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.
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.
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.
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.
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.
Personally, I don’ t understand the ‘pretty new mulch’ thing a all. I want to see plants in my garden, foundation plantings, etc – not bare mulch.
Planting beds with lots of bare mulch showing look like they have not yet become established.
Also, I prefer to mulch with ‘finished’ aka well-rotted compost. This is not ver combustable, though it does – like all organic matter – contain carbon, which as we all know – is something that can burn under the right conditions.
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.
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!
If a coal was flicked off a cigarette, how could investigators locate that?
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.
Cigarettes do a good job of non-spontaneous combustion of mulch too.
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.
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.
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.
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.
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. 🙂
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
Actually, it is the biological activity – fermentation – that causes damp (not wet) hay to heat to the point of combustion; not the moisture itself.
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
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. 😉
Hay is not bailed in the heat of the day. Early morning while the dew is on. This helps the leaves to stay intact. I am in a very dry climate though.
Hmmmm. Actually, the moisture levels in damp hay – usually not fully cured (not usually from external moisture like dew or rain) – allows fermentation to take place, which creates heat. The hay bales provide insulation which allows the heat to build up to the combustion point.
The same process can occur in compos piles, and often does in large piles of bedding and manure from horse stables.
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
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!
thanks, this is great info, i will be sure to water all esp against the house 🙂
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.
It sounds like the palm trees were being warmed by an active ‘hot compost’ type pile – fermentation being the heat source, with the right mix of organic matter fueling the process. This is VERY different from a thin layer of mulch on the surface of the soil.
The linseed oil used to treat the deck was no doubt the kind sold for the purpose in hardware and home improvement stores – which contain volatile petroleum distillates. These vapors coming off these products are highly combustible – like gasoline fumes. Instead, I would use 100% Tung Oil – the real stuff, with zero petroleum added. Hard to find, and not cheap, but it does a great job and is safe for use on food surfaces!
I like your theory about the magnifying glass. I wonder if a drop of dew could act as a lens despite being water?
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.
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.
Don’t forget about sunlight reflecting off windows of the neighbor’s or your own windows to focus sun light into burning beams .I had the west side of my house have burned spots in my zoysia grass. where the sun cast hot rays onto my neighbor’s upper windows with reflective tint that zoomed back into my yard. A bit further it could have hit my mulched rose bed, but luckily the trees tookpover for shade..
Here’s a follow up to my post with the actual article.
http://www.finehomebuilding.com/design/qa/melted-vinyl-siding.aspx
Don’t have time to read it now, but did the article mention just how horrifically toxic the fumes from burning vinyl are? Apparently the toxic compounds that result from burning vinyl (and many other plastics) persist in the atmosphere.
Sigh.
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!
I think I’ll go water my mulch.
Seems unlikely with constant rain our mulch should set ground on fire.
😉 sounds like one for mythbusters Mike!
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,
I’ve wondered about gazing balls acting like a magnifying glass to start fires. I love ’em but just wondered.
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.
John,
I had the same thought. I recall a few cases when I lived in Illinois where newly installed windows were enough to melt vinyl siding. They would probably heat the mulch to combustion too. Windows flex a bit and the new coatings make them somewhat reflective. So you end up essentially having a parabolic solar cooker with the focal point some distance from the window. If you put sunlight on the window and have vinyl siding at the focal point it can melt. I believe the same effect might be enough to ignite mulch.
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!
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.
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.
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.
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…
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.