Digger and Gina McLean
The Urban Myth of Mulch Landscape Fires.
We've all seen the posts on Facebook. Someone's mulch just caught on fire and burned their home! Horrific pictures of melted siding abound!
Really? In almost 40 years in the mulch business, we have never heard a report of it happening to any of our products, so I was really skeptical when I began to see these posts appearing on Facebook.
This month's blog will be focused on the science of mulch fires. I hope at the end of it, you will have a much better understanding and can be more informed when you see those scary Facebook mulch fire posts.
What we know is that mulch in large piles can heat inside to the point that fire can start. This is because as mulch decomposes it generates some heat and in big piles, that heat is trapped inside the pile and can ignite under the right conditions. As a mulch producer, we always have large piles of mulch on our yard and know it can happen at any given time, but the reality is that even though it can happen, it hardly ever does. It is really rare. Based on that fact then, in the landscape where you have just 3-4 inches in depth it would be really difficult to have enough heating for it to just start on fire.
This year, the Mulch and Soil Council, an industry association for mulch producers, hired the Southwest Research Institute to conduct a study to see if mulch in the landscape could catch fire. They did a months long in depth study of mulch combustion. The study found that mulch has to reach and sustain a temperature of almost 400 degrees F in order to ignite. In their landscape tests, even at it's highest temperatures in the summer months, mulch only reached a temperature of 113 degrees F. Not nearly hot enough to combust. Also, their testing found that it is much more difficult to get mulch to ignite than other materials like pine straw. In fact, the study results found that it is "very unlikely" for mulch to spontaneously combust in a landscape setting. Very unlikely.
So how do these stories about mulch spontaneously combusting get started? Well, someone might have a landscape fire, it gets reported and the cause is unknown, so people assume spontaneous combustion. Pictures are taken and put on Facebook. Then when the fire department does an investigation, they come up with the real cause but the facts are never reported. And, frankly, a spontaneous combustion story gets so much more traction on Facebook. Like a blurry picture of Bigfoot or Nessie, people want to like and share. But based on the science, landscape fires are started by some outside heat source, like cigarettes, overheating landscape lighting, etc. and not spontaneous combustion.
So, hopefully, you come away from this article more informed about mulch and fire. We hope you'll keep using the mulch you love to prevent weeds and retain soil moisture. And next time you see that scary Facebook post about somebody's mulch that spontaneously combusted, you can know it's not true and just keep scrolling.