Is Mulch A Fire Hazard? How To Stay Safe


I have had my fair share of mulch in the last few years. And while it has had significant effects on my gardening and landscaping activities, it has its downside. Due to this, I decided to research just how much of a fire hazard they can be.

Well, your fears are founded. Mulch is flammable and might be very challenging to extinguish as soon as it ignites. As such, it’s essential to maintain safety precautions to prevent a fire outbreak. For example, you might need to reduce the proximity of your mulches to physical structures and then wet them during the dry season.

However, while mulch is flammable, the degree of fire risk depends on the type of mulch. For example, mulches that generally have increased oil content ignite easily and faster than others. Also, some mulches have a higher propensity to ignite when exposed to certain materials.

As such, it’s necessary to have a good idea of your mulch type and its risk propensity.

Does Mulch Pose A Risk of Fire Hazard?

The fact is that mulch poses a risk of fire hazard. And it catches fire when it’s hot to a certain degree.

Mulch releases embers that fly around and lands on various surfaces, and when the new location is naturally combustible – for example, dry leaves or dry grass – a new fire starts.

Also, the fire risks vary based on the type of mulch and how you have it arranged. However, generally, critical findings of the fire risk of mulches suggest the following.

  • Mulches are generally combustible during dry seasons.
  • Pine needles and shredded rubber has the highest risk of a fire hazard.
  • Tahoe chips and compost wood chips, when applied in a single layer has the least risk of a fire hazard.
  • Shredded rubber mulch burns at an average highest temperature of over 380o F. It produces the highest flame heights at an average of more than 3 feet when placed four inches over the mulch floor. It also ignited faster and burned for a more extended period.

Also, evaluating the potential of mulches to catch fire, the University of Nevada Cooperative Extension carried research. Here’s the result.

Mulch TypeDescriptionFire Potential (Average maximum flame height)Fire Potential (Average maximum rate of spread)Fire Potential (Average maximum temperature 4 inches over the bed)
Composted Wood ChipsWood chips were placed at a depth of 2- to 3-inches. And it was composted for eight weeks utilizing a proprietary process.403735
Medium Pine Bark NuggetsIt was placed at a depth of 2- to 3-inches. And it consisted – 75% – of pine bark parts with a diameter of almost 1 inch.1206052
Pine NeedlesPine needles were placed at a depth of 2- to 3-inches. And it consisted, between 80 and 90% of pine trees. The remaining 10 to 20% then consisted of leaves, wood chips, cone scales, and twigs.20515560
Shredded RubberShredded Rubber was placed at a depth of 2- to 3-inches. And it consisted of 100% rubber that was recycled, dyed, and refined to imitate redwood mulch.225125100
Shredded Western Red CedarIt was placed at a depth of 2- to 3-inches. And it was manufactured from red cedar – western – and 5% wood chips.19016560
Tahoe ChipsIt was placed at a depth of 2- to 3-inches. It is comprised of wood chips, pine needles, plant biomass, and bark. However, their texture and shape weren’t uniform.1157560
Tahoe Chips with fire retardantIt was placed at a depth of 2- to 3-inches. It is comprised of wood chips, pine needles, plant biomass, and bark. However, it was sprayed with a fire retardant/wood colorant solution. And it was sprayed at the rate of 1.25 gallons per 50 square feet.905252
Tahoe Chips (single layer)Tahoe Chips were placed using a one-layer depth. And this layer provided between 80 and 100% floor cover. Generally, it consists of wood chips, pine needles, plant biomass, and bark.523830

Without a doubt, it’s clear that mulches pose a fire hazard regardless of your choice of mulch. And the only difference is that while some pose a higher risk, others pose a lower risk.

How to Stay Safe and Prevent Fire Outbreaks from Mulch?

Although mulches create a risk of fire hazard, you can reduce this risk to the barest minimum. And this is particularly necessary since mulches are an essential part of our gardening and landscaping activities.

So, to stay safe and reduce the risk or prevent fire outbreaks from mulches, the following safety precautions are useful.

1. Use Mulches That Are Less Prone to Ignition to avoid fire

One of the best ways is to stay safe is to use less flammable mulches. And this is because since they are less likely to ignite themselves, you can avoid fire outbreaks.

As such, it’s best to use composted wood chips in residential areas, for they have reduced combustibility.

Woodchips are known to be bigger in size and bulkier than mulch. And has many benefits in both gardening and landscaping practices. A comparison of both advantages and disadvantages is detailed in this article that I wrote on mulch vs.. wood, which you can check through this link.

Also, you don’t need to worry about a corresponding price increase. So, composted wood chips are pretty much readily accessible. Still, they are combustible, so ensure you apply ignition-resistant items in between them.

2. Arrange Your Mulch Strategically to avoid fire

Another thing to note is arranging your mulch strategically and thus reducing its risk of fire hazards. For instance, spreading your mulch as a thin layer minimizes the likelihood of heat. As such, apply your mulch with a thickness between 2 and 10 centimeters.

Also, as stated above, some mulches are more flammable than others. It can be quite dangerous to arrange them continuously.

In this instance, the best bet is to separate highly combustible mulches by placing ignition-resistant items. This way, in the case of ignition, the possibility of fire spread can be reduced.

3. Maintain Effective Distance with Combustible Materials to prevent fire

As already stated, mulches, when hot or after igniting, may fly around as embers. And in turn, when it lands on combustible materials, it creates a new fire. As such, to reduce the risk of a fire outbreak, it’s better to ensure that no combustible material is around. This way, your mulch’s embers will not result in more fire.

To ensure that the mulches will not catch a new fire and further damage your property, there must be a distance of 18 to 30 feet between your landscape mulch area and the nearest combustible materials.

Pay special attention to electrical devices like decorative lights.

4. Avoid Using Mulches Near Your House to avoid fire

Another critical way to stay safe is to ensure your property is far from your mulches. This is important because it’s quite risky to want your garden close to your house.

Keeping your mulch too close to your property increases the risk of a full-fledged fire outbreak. And this is thanks to the destructive capacity of mulch embers. As such, ensure your property is also at least 30 feet away from your mulch.

However, in case you have mulches close by, ensure they are ignition-resistant and non-combustible mulches. For instance, well-irrigated plant materials and nicely maintained flowers and lawns might do the trick.

5. One way to prevent fire is to keep Your Mulch beds moist

To ensure your safety from a fire outbreak, it’s vital to keep your mulch beds wet. And this is particularly relevant during the dry season. This is because this period increases the likelihood of your mulch igniting.

As such, regularly water your mulches to prevent fire outbreaks.

The use of an irrigation system is generally a great idea. This way, you can effectively keep the area wet.

6. Maintain Surveillance on your mulch to avoid fire

Another consistent routine to stay safe is to maintain proper surveillance of your mulches. And this is particularly relevant in the period when the rainfall is below average, or the temperature is warm. This is because your mulches are more likely to ignite during this period.

Through regular surveillance, you can tell when they get hot. Make sure to get them moist during those instances. Also, in cases where they ignite, you can promptly put them off before they spread to other parts of the house and cause real destruction.

7. Avoid Discarding Smoking Materials on Mulches to avoid fire

The negligent dropping of smoking materials on mulches has contributed its fair share to recent fire outbreaks. And this is primarily due to various smoking policies that prohibit smoking within facilities.

To reduce the risk of fire outbreaks, avoid dropping your smoking materials on mulches and instead utilize receptacles to discard your cigars or cigarettes.

Also, where necessary, ensure that there are proper trash cans available close to your mulch area. This way, you can reduce the risk of outsiders dropping smoking materials on your mulch.

8. Store Mulch Properly to lessen fire hazards

It can be quite dangerous to store or pile mulch around, especially for a long time. Ensure that they are always appropriately stores and avoid having high piles of them.

Constantly reduce the height of the mulch collection and break the pile into smaller piles.

Also, avoid placing the piles under the sun directly. This increases the heat buildup within the pile, one which increases the possibility of ignition.

What Are Mulch Fires?

Each year, the United States of America records over a thousand mulch fires. And this is more prominent during the warm or dry season.

Generally, it involves a situation where mulches ignite or catch fire due to different reasons. These fires can either be small or big. In cases where it’s small, you can easily put it out. However, in instances where it’s big, it can be quite daunting.

In big mulch fire cases, it becomes a public concern as it may extend to structures and houses and result in a threat to human life.

Big mulch fires also result in the loss of thousands of dollars. For instance, there is existing legislation in some states that require mulches to be a minimum of 18 inches far from buildings.

What Are the Risk Factors That Causes Spontaneous Combustion?

As stated throughout this post, mulch is generally flammable and may ignite. However, certain factors increase the risk or cause spontaneous combustion. They include:

Factors that increase the risk of spontaneous combustionExternal factors that may result in your mulch catching fire
Mulch piles of more than 20 feetCareless use of cigarettes or cigars
Dry mulch piles – between 20 and 40% moistureLIghtening
Static piles which remain unmoved for monthsArson
Dry weather conditionsWildfires
Feedstock materials with oil and resinsImproper procedures, for example, welding sparks from equipment repair close to a mulch pile.

It is best to always be on the look for this factor to prevent accidental fires.

How an Ignition of mulch Occurs?

You might be wondering why mulches pose a fire risk. And although it appears complicated, it’s quite simple and occurs in a somewhat step-by-step process.

This process begins with the mulch pile getting heated up as a result of microbial activities. As microbes decompose organic materials, heat is produced and lost.

Extreme cases that cause mulch fire

However, in cases of extreme external heat, either due to the weather or the pile’s size, it becomes hard for the pile to lose heat fast. And as such, it retains more heat, which increases its temperature. When this process continues unhindered, the temperature continues to rise until it reaches a dangerous stage.

Now when the temperature reaches about 1800 F, there’s a stop to microbial activities. And in its place, abiotic processes take over.

Precisely, decomposition is done without oxygen and through heat. And then, since the compounds involved in this process are highly flammable, the introduction of oxygen causes an ignition.

How to Fight Mulch Fire to Prevent Spread?

Although it’s best to avoid ignition in your mulches, it is impossible to rule it out. It becomes crucial to put it out as soon as possible to avoid further spread in such cases. And to do this, specific points are vital.

First, it’s crucial to have planned ahead of time. And this is because fires, although unwanted, are a common occurrence. As such, ensure you have an understanding of your fire department before its event.

In any case, water application to the pile’s surface while also opening the mulch pile collection is an effective strategy for putting out the fire.

When utilizing this technique, ensure you have applied water to the surface of the pile before opening it up. This is because opening the pile introduces fresh oxygen. Its introduction can result in an increased spread of the fire across the mulch.

Also, vast amounts of water might be ineffective in most instances. As such, apply the water selectively and in hotter locations. You can also use chemicals that suppress a fire, for example, foams.

FAQs

Conclusion on mulch being a fire hazard

We would never want to have our properties and gardens ruined by a mulch fire. Not only is it a traumatic experience to us, our neighbors, and also most possibly our lawns and gardens, it also causes so much destruction of our garden’s original state and loss of money that we put into fostering our spaces.

That is why it is always best to keep a watchful eye on our mulch piles. Take care to constantly wet it, especially if you live in hotter climates, and keep it away from your flammable properties. Also, make sure to keep it away from your barns and our poultry spaces so that it won’t cause possible harm to your animals and livestock.

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Tony O'Neill

I am Tony O'Neill, A full-time firefighter, and professional gardener. I have spent most of my life gardening. From the age of 7 until the present day at 46. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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