Can Grass Clippings Cause A Fire?

Mowing your lawn comes with a caveat. That caveat is grass clippings, and although some people just leave them in their neat little rows, others try to figure out things to do with them. No one thinks of lawn clippings as inherently dangerous. However, there is one danger that everyone would do well to consider. 

Grass clippings are notorious for becoming fire hazards, and they have done damage that is newsworthy in the past. Grass clippings can catch fire and cause thousands of dollars in damage. The threat is real enough that warnings are issued on the news throughout any dry spells. 

It doesn’t exactly take a match or a flicked cigarette to start a fire, even though that is the cause of roadside fires after state workers mow the medians and shoulders. Fresh grass clippings also generate their own heat as they undergo the process of fermentation.

Why are Grass Clippings Fire Hazards?

In May of 2014, a fire raged through a home of four in California. It did $150,000 worth of damage to the house and the surrounding property before being extinguished. 

When firefighters arrived on the scene, they discovered the fire started because of a garbage can full of grass clippings adjacent to the home. 

There was no match, lighter, lit cigarette, or any other fuel involved. The grass clippings and surrounding trash generated enough heat to reach the flashing point. 

If you’ve ever processed your own compost, you know the power of heat generation from decaying, organic matter. 

Grass clippings do the same thing, and they are actually an excellent addition to a composter when you need to generate some additional heat. 

However, when disposed of irresponsibly, the heat they generate is not good. 

While grass clippings alone will not heat up enough to reach the flash point of dry grass, they can certainly do so when combined with garbage. Also, once the grass clippings are dried out, which only takes a few days, they are highly combustible, and all it takes is a spark to ignite them. 

Why do Grass Clippings Get so Dry?

Grass clippings, like any other dead organic matter, go through a decomposition process. Throughout this process, they can get exceptionally hot. In fact, under the right circumstances, they can get hot enough to make you drop them in a hurry if you get your hands on some. 

Once cut, grass clippings go through a process of fermentation, which is essentially useless for most gardening techniques because grass clippings have very little in the way of vitamins and nutrition. Furthermore, the fermentation process quickly passes within a few days.

As they continue to lay there, only a few more days are sufficient to make the grass clippings extremely dry. They are no longer hot at this point, but they’re still dangerous because the flash point threshold to light them on fire is much lower. 

If it has been warm and dries out for a long time, it’s never a good idea to mow your lawn when the previous cut’s grass clippings are still there. This is because the lawn mower may not get hot enough to ignite the grass clippings.

However, all it takes is a single spark from the spinning blades striking something—like a hidden rock in the grass—to light those clippings on fire. 

Once lit, it’s like a trail of black powder. Fire, like electricity, always takes the most straightforward path unless it is forced by wind or other elements to do otherwise. 

The fire will rapidly move up the trail of grass clippings burning the clippings along with the green, fresh grass of your lawn. If any clippings are close to your house or, worse yet, close to a treated deck, things can get ugly in a hurry. 

Grass clippings are not a slow-burning fuel for a fire. On the contrary, the fire burns quickly, feeding on the fuel very fast, and it burns hotly. It’s kind of like throwing lighter knots in your fire. It burns ferociously and hot but leaves very little in the way of hot coals behind it. 

Properly Dispose of Your Grass Clippings

First and foremost, never toss your grass clippings in the garbage with the rest of your trash, even if you own a larger dumpster. The combination of superheated grass clippings and the heat generated from decomposing trash can be ferocious. 

If you have any residue of household chemicals in the trash, it can get nasty in a hurry. You should also avoid piling clippings or storing your bag of clippings near your home, and never let grass clippings sit out in the sun if you can help it. 

There are much better ways to dispose of grass clippings or actively use them instead of leaving them lying around or storing them improperly. 

  • Use your excess grass clippings in your compost drums.
  • Feed them to your livestock (only when the clippings are fresh and untreated by herbicides)
  • Burn them in a controlled burn
  • Separate them and use them as a combination mulch
  • Mix them in fresh soil for garden use
  • Bag your grass clippings separate from your trash and lay them out in accordance with your local county/city rules or guidelines

Grass clippings, as extensively noted above, are excellent at generating heat, which makes them very useful in a compost drum. This is especially true if you have difficulties generating the right heat temperature for your composting projects. 

If you ever have a backyard burn, to get rid of old tree branches and twigs (especially after a storm), you can burn them. One of the best ways to conduct a controlled burn is to purchase 50-gallon drums that are completely empty.

Cut yourself a 6″ x 6″ square just above the bottom rim of the drum to create adequate oxygen intake, and you have one of the cheapest and easiest backyard burning mechanisms you can find on the market. These drums are excellent for burning backyard debris, and you can safely burn off your grass clippings. 

Some people like to use grass clippings as a form of cheap mulch. They retain water well and provide a protective barrier for freshly planted vegetables or flowers. Just make sure that the grass clippings are in small quantities and well-separated. 

They’re also useful if you want to mix them in with fresh garden soil, as they will help hold water for the new roots to take hold. 

Lastly, if you have no use for your grass clippings, bag them up in a lawn bag, completely separate from any other garbage, and set them out for the garbage crew to pick up. Just be sure to follow your local county or city guidelines, especially during dry weeks/months. 


Grass clippings are a fire hazard; you should always treat them as such, disposing of them in one of the above-listed methods. It’s always best to use or dispose of them correctly, rather than leave them lying around or storing them away. 

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