What to Consider Before Laying Rubber Mulch

Katy Willis
Written by Katy Willis
Updated July 20, 2021
Woman smiling in garden
Jacob Lund/Shutterstock.com

Recycled rubber mulch has a lot of benefits—but it’s also controversial

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While mulch typically consists of organic matter (think wood chips, shredded leaves, or straw), repurposed rubber mulches are increasingly common. But recycled tire mulch is controversial, too—some people love it because the bugs just bounce right off the rubber (OK, they don't actually bounce, but they do find it less hospitable than organic mulch). 

The anti-rubber-mulch faction points to concerns over chemicals leaching from the rubber and contaminating the soil. This guide explores the pros and cons of rubber mulch so you can make up your own mind and choose the right mulch for your garden.

The Benefits of Rubber Mulch

Rubber mulch usually looks just like wood mulch, but it’s also available in a variety of colors and textures for those who want a different look for their landscaping. Along with its unique aesthetic, it's also gaining in popularity for its benefits.

Rubber Mulch Has a Long Life Span

Rubber mulch isn't organic, so it lasts much longer than wood, straw, and leaf alternatives. Some manufacturers claim their rubber mulches can last up to 10 years before you need to replace them. Wood mulch, on the other hand, breaks down completely in four to seven years.

Rubber Mulch Doesn't Absorb Water

Organic mulches tend to absorb and hold onto a lot of water, which can result in a hub of fungi, mold, and pathogens. Rubber mulch, on the other hand, isn't absorbent at all. Water simply passes around the mulch and straight into the soil, keeping plants thoroughly hydrated.

Rubber Mulch Doesn’t Attract Most Bugs

One big advantage of rubber mulch is that it doesn't attract many bugs—with one exception (we’ll get to that later). But, in general, if you have serious pest problems and you're trying to avoid ant or termite infestations, rubber mulch can help by not providing them a suitable home.

Rubber Mulch Doesn't Blow or Wash Away Easily

Rubber mulch is made from ground-up tires and tends to be heavier than its organic counterparts. Therefore, it's not typically blown away by strong winds or swept out of your garden bed in heavy rain. With wood and straw mulches, you can accidentally blow them all over the place just by being a little too enthusiastic with your leaf blower. You won't have this trouble with rubber mulch.

Rubber Mulch Helps Inhibit Weed Growth

Mulch is primarily used to inhibit weed growth, and rubber is the all-star. The material is heavy and dense, so it blocks light and compresses the soil surface, discouraging weeds from germinating or pushing up new growth. And it'll help you in your fight against your neighbor's weed seeds, too—because it doesn't hold water, rubber mulch is inhospitable, holding and dehydrating the weed seeds before they can germinate and take root in your soil.

Rubber Mulch Is a Good Insulator

Well-known for its insulating properties, rubber can hold warmth in your soil for longer. This can extend plant growth and warm the earth earlier in the year for a significantly increased growing season. Plus, you'll get earlier flowers that will keep flowering later into the fall as the soil retains its heat thanks to the rubber mulch blanket.

The Disadvantages of Rubber Mulch

As with anything, rubber mulch isn't without flaws. Delving into the disadvantages of rubber mulch can help you decide if it belongs in your garden.

Rubber Mulch Is Pricey

Rubber mulch is fairly expensive compared to other inorganic and organic mulches, at approximately $120 per cubic yard. For comparison, typical pine bark mulch costs $30 per cubic yard.

Rubber Mulch Can Be a Fire Hazard

In spite of some manufacturer's claims, rubber mulch is flammable. In multiple tests, it's proved to burn hotter and faster than wood mulch. It spread faster and was more challenging to extinguish because of its comparatively high carbon to nitrogen ratio. Therefore, if you live in an area of elevated fire risk, avoid rubber mulch and opt for an organic mulch that's more difficult to ignite and slower to spread.

Rubber Mulch Is Difficult to Remove

Because it's inorganic and takes many, many years to properly break down, rubber mulch has to be kept separate from the soil. You’ll need to add a layer of hard wearing landscaping fabric between the two layers. 

If the landscaping fabric splits or you make the mistake of foregoing the barrier layer, letting the rubber mulch and soil mix, you may need to hire a local professional landscaper to remove the entire top layer of soil. This way, you can be sure you get rid of all the rubber. 

Also note that this means you cannot till anywhere you've laid rubber mulch, as you cannot work it into the soil. This makes cultivation and weeding much more challenging.

Rubber Mulch Contaminates Soil

Rubber from tires contains many chemicals and heavy metals, even if it’s undergone extensive cleaning and preparation processes. Aluminium, zinc, cadmium, chromium, and more can all leach into the earth as the rubber breaks down, contaminating your soil. 

Heavy metals are linked to serious health conditions in humans and animals, including cancers and neurological conditions. And the contamination isn't localized, either. Yes, your soil can suffer, but the heavy metals eventually also leech into the groundwater, too, causing widespread contamination. 

Because of the risk of chemical and heavy metal contamination, you should not grow anything you plan to eat in soil that has—or had—rubber mulch applied, as the contaminants can end up in your produce, and you really don't want to eat it.

Rubber Mulch Has Potential Health Risks

In mulch form, recycled rubber releases volatile organic compounds, or VOCs. These gaseous compounds are dangerous if inhaled and can lead to long-term health complications, ranging from nausea and dizziness to kidney, liver, and neurological damage. VOC increases as the rubber warms up, making the mulch undesirable for hot climates.

Rubber Mulch Can Harm Plants

Zinc is a particularly problematic heavy metal for flora and can accumulate in the plants you grow, slowly killing them. Similarly, chemicals added to the rubber can leach into the soil, harming your plants, damaging soil health, and unbalancing the micro ecosystem of your garden.

Rubber Mulch Harbors Some Insects

While rubber mulch is not attractive to most pests, a study published in the National Library of Medicine found that it's the favorite mulch of Asian cockroach mommies and their babies—yikes! So if your area is prone to these pests, it's not advisable to offer them a five star hotel in your backyard.

Rubber Mulch Is Susceptible to Specific Fungi

For the most part, because it's inorganic and doesn't absorb water, rubber isn't susceptible to molds and fungi ... that is, except for species of brown rot and white rot fungus that attack the mulch’s chemical additives.

Rubber Mulch Doesn't Replenish Soil With Organic Matter

Even though rubber eventually breaks down into smaller particles, it doesn't add useful organic matter to your soil. In fact, as you've already seen, if rubber mulch does get into your soil it's a costly issue to fix. 

Organic mulches break down quickly and add fibrous matter and valuable nutrients to the soil, replenishing the quantity and quality of your topsoil. Organic mulch is also easy to till into the soil, improving drainage and soil structure quickly and easily. 

Rubber mulch is a controversial product that can be useful in some situations, but you have to consider whether the cost, health, and environmental implications outweigh the benefits. If in doubt, contact a local mulching company to find out which type of mulch would be best for your garden, and how much mulch you need.

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