An Ontario gardener's morning commute took a bizarre turn when a glance at a potted plant made them think it was on fire after a cold, rainy night.
A short video posted to Reddit's r/gardening set off a wave of theories about what could make damp soil appear to smolder.
(Click here if the embedded video does not appear.)
The poster said they woke up to a startling sight in Ontario, Canada: a container plant that seemed to be burning despite chilly, wet weather overnight. "I woke up this morning and as I'm on my way to work I noticed my potted outdoor plant is on fire," they wrote.
The post drew more than 3,000 comments and quickly turned into a crowdsourced gardening mystery. Some Redditors guessed that someone may have tossed a cigarette butt into the planter, while others pointed to a less obvious explanation involving compost-rich soil heating up and reacting with fertilizer.
The OP explained that it didn't appear to be from a cigarette, at least with no evidence of one in or near the plant, so the most likely cause may be composting.
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One commenter shared a detailed theory, suggesting that fermenting compost may have generated enough heat to trigger a smoldering reaction.
"Although it may sound wild, it could be possible that the fermenting compost in the soil released enough heat to make the ammonium nitrate (fertilizer) pyrolyze (decomposing due to heat, into flammable gases). This caused a smoldering combustion, often seen in underground wildfires, where the roots slowly pyrolyze, barely consuming any oxygen, and not emitting any light, thus called "invisible fires."
Whatever the exact cause, the gardener later said the danger seemed to be coming from beneath the surface, not from the plant itself. Even small backyard or balcony setups can pose fire risks. A container pot placed near a home, fence, or deck can become a much bigger problem than it first appears, especially if the heat is coming from the soil rather than visible flames.
If you garden in pots or raised beds, it's worth checking containers regularly, especially after adding fresh compost, fertilizer, or other organic material. If a pot seems unusually warm, smoky, or smells like something is burning, it's best to move carefully and treat it as a potential fire hazard.
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It also helps to keep planters away from walls, railings, or dry materials when possible, and to avoid tossing cigarette butts anywhere near soil, mulch, or containers. If you're using homemade compost, make sure it is fully finished before mixing it into pots.
Knowing what's in your soil blend can also make a difference. Fertilizers, especially strong synthetic ones, can behave differently when exposed to heat and moisture. Reading labels, using products sparingly, and storing them properly can help reduce the risk of dangerous reactions in tight residential spaces.
"We put it out," the poster later wrote. "The soil was more on fire than the root ball of the plant."
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