While mulching is not an unusual or unfamiliar gardening practice, many people are still unaware that it can spontaneously catch fire while sitting in the garden. On Vashti’s video only, dozens of viewers flocked to say that they were ignorant of the mysterious nature of mulch. “I have been around mulching my whole life. I'm from Australia and I have never heard of this,” said @jemmabeth. @habsfan2567 wrote, “I’ve never heard of mulch spontaneously combusting. We’ve had mulch in our gardens for over 25 years.” While you’re yanking invasive weeds, you might not notice that heap of dead grass and parched leaves may be slowly accumulating heat energy that will soon explode.
“Wood shavings that are normally dyed dark brown or black, we put on our flower beds,” explained @markiplacehq. @hibadeehoopla described it as “a thin layer u put on top of soil, helps growth and prevent weeds.” USDA defines mulch as “a protective layer of a material that is spread on top of the soil.” Mulch can be either organic, like grass clippings, straw, and bark chips, or inorganic materials like stones, gravel, brick chips, and plastic.
Tons of viewers who work in firefighting jumped into the comments section. “Hubby is a firefighter, sees it a lot. Please water it twice a day,” shared @dozzers_momma. A firefighter, @guyfieri, said, “We get hiked out for mulch on fire frequently in the summer.” @tashapulatiehead shared that she witnessed her cousin’s house set aflame from smoking mulch.
@huntress_horsemanship shared that it can happen when the heat in manure piles gets crazy. In the video, Vashti detailed the science behind why and how this curious phenomenon unfolds all by itself. In cases when mulch is primarily composed of organic matter, the fire erupts due to a chemical reaction called “oxidation.”
Explaining this, Vashti said, “As these organic materials break down and decompose, oxidation occurs, and this process is what generates the heat. Now, when you have a pile of these materials that is too thick, oxygen can become trapped in that pile. You can also have certain weather conditions. So this can happen even when it’s freezing outside. It’s due to oxygen. So if there’s a slight breeze, if you have had no rain, you have excessive dryness in your area, that heat that is generated is combined with that oxygen, and this is what creates a fire.”
Vashti revealed that the fire doesn’t happen only with mulch. “It can happen with uncoloured mulch or coloured mulch, but it can also happen to piles of wood chips, bales of hay, your compost piles,” she told the viewers. However, there are some alternatives. According to experts at Lawn Love, some of the mulches that carry the lowest risk include composted wood chips, shredded rubber mulch, stones, or gravel. The ones with the highest risk are pine needles, shredded bark, dry leaves, or straw.
You can follow Kayla Vashti (@kaylavashti) on TikTok for DIY project videos.
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