Homesteading, Gardening, and Off-Grid Living

How to Use Cedar Mulch to Repel Bugs and Other Pests?

By: Zac Friedman

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Cedar is a beautiful and long-lasting type of mulch that is commonly used in landscaping. Some gardeners choose cedar mulch for its insect-repelling properties. Cedar mulch can be used to repel unwanted pests such as mosquitoes, ants, termites, aphids, cockroaches, and ticks. There are natural oils in the cedar that create an odor that certain pests don’t like. It acts as a natural pesticide. 

One common concern is that cedar mulch will repel beneficial bugs. Specifically pollinators like bees. Some also worry that it will reduce earthworm populations. Some are simply skeptical about whether or not it actually repels pests at all.

Does cedar mulch repel bugs? Will it also repel bees? In this guide, we’ll look at the science to answer these questions more in-depth. 

How to Use Cedar Mulch to Repel Bugs and Other Pests

Does Cedar Mulch Repel Bugs?

The short answer is yes. Cedar mulch will repel some pests but not all. It can help keep ants and termites out of your garden. It does not repel bees but it can repel other pollinators. Cedar does not affect earthworms. Generally, cedar mulch does a better job of repelling crawling insects than flying insects. 

Some pests dislike the smell of cedar so they stay away. Some are sensitive to chemical compounds within the cedar oil. Cedar trees do still suffer from pests. This means that not all insects dislike the smell of cedar. 

Some gardeners claim that cedar is toxic to certain pests and that it can prevent some species of plants from germinating. This is not true. Cedar will not kill any garden pests or plants. It can just slow them down. At high concentrations, cedarwood oil can kill certain insects. 

Cedar mulch isn’t all that effective at repelling bugs from flower beds because the smell dissipates quickly in the open air. As cedar mulch ages and starts to decay, the smell goes away. It doesn’t last forever. If you want to use cedar mulch to repel insects, you’ll have to replace it frequently to keep it fresh. 

Red cedar mulch
Red Cedar mulch

How Does Cedar Mulch Repel Pests?

Cedar mulch contains essential oils that naturally repel insects. Basically, certain insects don’t like the smell of cedar so they stay away.

The main insect-repelling chemical found in cedar is called Thujone. This chemical is found in many different types of plants and trees including cedar. Thujone has been tested in scientific studies. It has been proven to repel certain bugs. 

For example, this study tested the effects of Thujone on aphids. The study found that “β-Thujone lactam can be considered a deterrent of medium potency with activity expressed at preingestive phase of aphid probing.” 

It’s important to note that this study used a concentrated extract of Thujone. It did not use cedar mulch. Cedar can act as a pesticide. Just not a very strong one.

What is Cedar Mulch?

Cedar mulch is made from chipped or shredded cedar trees. Both the bark and wood of cedar trees can be used to make mulch. The mulch is spread across the surface of the soil in a layer 2-4” deep. 

Cedar trees are evergreen conifers. A few types of cedar trees used to make mulch include the western red cedar (Thuja plicata), eastern red cedar (Juniperus virginiana), and northern white cedar (Thuja occidentalis). Red cedars are the most common. 

Cypress trees can also be used for mulch. They are similar to cedar but not the same. Cypress mulch may also have pest-repellent properties. 

Cedar Mulch and Bees

A beekeeper

One of the most common concerns for gardeners is that cedar mulch will repel pollinators, like bees. Some argue that bees stay away because they don’t like the smell of cedar. I have even read claims that cedar kills bees. 

This isn’t the case. Cedar mulch does not repel bees. In fact, cedar wood is one of the best types of wood to build bee boxes. Beekeepers use it all the time. This is because it is resistant to rot and it can also help keep pests away. Western Red Cedar is commonly used. Some beekeepers even lay cedar mulch around their bee boxes to keep pests away. 

Cedar Mulch and Ants

Cedar mulch can help to repel ants. According to this study from The National Library of Medicine, “Our results suggest that aromatic cedar mulch may serve as an effective component of a comprehensive urban ant management program.” 

This study tested the effect of cedar mulch on the Argentine ant and the Odorous House ant. It found that the house ant avoided the cedar mulch for nesting. Both species of ants were also killed when they were confined in containers filled with aged cedar mulch. 

This study proves that cedar mulch can help to control an ant problem. This is probably because ants are not flying insects. They have to walk through the mulch. Different types of ants may respond to cedar differently. 

Cedar Mulch and Mosquitoes

One common reason people use cedar mulch is because they believe it will help repel mosquitoes from their yards. The idea is that the mosquitoes don’t like the smell so they stay away from the mulched areas. If it worked, this would be great for an outdoor space like an outdoor kitchen. 

Unfortunately, it may or may not work. The information I have found is conflicting. According to this study from the National Library of Medicine, cedar oil did not repel mosquitoes. In their test, only peppermint oil repelled mosquitoes when used in high concentrations. 

This article from the USDA had different results. It claims that cedar can repel houseflies, ticks, and mosquitoes. It even claims that it kills them. Cedar may reduce the number. It may do nothing.

Cedar Mulch and Termites

Termites in garden

Cedar mulch can help keep termites away. In this study, termites were given different types of mulch as food. They chose cedar less than other types of mulch. Cedar doesn’t kill termites. Termites simply prefer other types of wood over cedar. If given the choice, they will not eat cedar.

If you have a termite problem, cedar mulch may help. At the very least, it won’t attract them. Termites can still use cedar as a food source. There is nothing stopping them from eating it if nothing else is available.

To reduce the likelihood of a termite infestation, you should never mulch right up to your house. You should leave a gap of 12-18 inches so termites and other bugs can’t make their way into your home as easily. 

Cedar Mulch and Rodents

Cedar mulch may help if you have a rodent problem in your yard. According to this article from the Seattle Times, “When mice and other rodents are exposed to cedar mulch, chips, or shavings, the toxic phenols are absorbed through the respiratory tract and enter the blood system, fatally damaging the liver. The acids released are damaging to the animals’ lungs and trachea.”

Rats and mice usually won’t nest in cedar mulch for this reason. If you have had problems with rodents nesting in your garden, switching to cedar might help.

Cedar Mulch and Snakes

Cedar mulch may help repel snakes. Snakes find the smell of cedar unpleasant. The chemicals in the cedar oil can irritate the snake’s lungs. Cedar won’t prevent snakes from coming onto your property but it may help to keep them away. It also won’t harm snakes. 

Cedar Mulch and Invertebrates

Invertebrates include creatures such as earthworms, snails, slugs, spiders, centipedes, millipedes, and beetles. Insects are also invertebrates. Cedar mulch can repel some invertebrates but most are not affected. 

If you’re worried about cedar mulch repelling earthworms, don’t. Mulch helps to protect the soil and keep it moist. This is beneficial for worms. The worm population in your soil may actually increase if you cover the soil with mulch. It doesn’t matter which type of mulch you use.

Cedar Mulch and Pollinators

Some gardeners worry that cedar mulch will repel pollinators from their yard. This is a rational concern. If pollinators don’t come, your yields will decrease. This would be a serious issue if you’re growing food.  

I have not been able to find any evidence that cedar mulch repels pollinators. Personally, I don’t think it would have an effect because flowers are elevated away from the mulch. Most pollinators are flying creatures. They don’t have to walk across the mulch. As mentioned earlier, cedar mulch won’t repel bees.

Chilis growing in a raised garden bed
If pollinators don’t come into your yard, your vegetable plants won’t be as productive

Do Cedar Closets and Chests Repel Insects?

In some homes, the closets are lined with cedar boards. Some old chests of drawers are made from cedar or lined with cedar. The idea is that the cedar would repel cloth-eating moths and other insects that can damage clothing because insects don’t like the smell of the cedar.

There are a few studies that have tested the efficacy of cedar closets but they are outdated and inconclusive. 

According to this article from the University of Kentucky,  “​​Contrary to popular belief, cedar closets or chests are seldom effective in deterring clothes moths because the seal is insufficient to maintain lethal or repellent concentrations of the volatile oil of cedar.”

This article contradicts the other. According to this article, “cedar chests are effective, but primarily because of their airtight seals. It’s unlikely that the cedar linings on their own would be effective against moths or their larvae. In any case, cedar oils lose volatility as the wood ages.”

It seems to be a bit of a myth that cedar closets and chests will protect your clothing. The cedar may have some effect when it’s new. The problem is that cedar loses its insect-repelling oils over time. It doesn’t smell as strong after it ages. You can sand the cedar down to restore some of the scent but you probably wouldn’t want to do this regularly.

To be effective, the cedar closet or chest would need to seal up airtight to keep the insect repelling chemicals inside at high enough concentrations. Most closets and chests also don’t seal up to keep airtight. 

If a cedar box isn’t effective at repelling insects then the cedar chips in your garden beds probably isn’t either. The insect repelling compounds just blow away in the wind. Cedar mulch also ages quicker because it’s outside. The chemicals quickly dissipate as the cedar starts to decay. 

There still is one benefit of cedar closets. They smell nice. My last home had cedar lined closets. I loved walking in every morning and getting a breath of the woodsy aroma of cedar. 

Cedar Mulch Degrades Over Time

If you choose to use cedar wood chips for their pest repellant properties, keep in mind that it won’t last forever. Over time, the odor dissipates as the mulch degrades. It is organic matter, after all. It will decay. The weather washes the oils away. Particularly if you live in an area with heavy rainfall.

Cedar mulch may only offer pest repellent properties for a year or so. After that, the odor will be much milder. You can refresh it by adding a new layer of mulch on top of the old mulch. 

A pile of mulch next to a wheelbarrow

Should You Use Cedar Mulch?

Cedar mulch can be a natural way to repel some types of insects such as termites and ants. It may also help keep rodents and snakes away. It isn’t really effective against flying insects. Cedar doesn’t seem to repel pollinators. It won’t affect earthworms. 

Overall, cedar mulch is a good choice for your yard. It has some natural insect repellent properties. It won’t keep all pests out of your yard. If you have a serious pest problem, cedar mulch won’t solve it. It’s just not strong enough. You’re better off using pesticides. 

There are plenty of other reasons to use cedar mulch. It’s a beautiful groundcover. Cedar has a nice reddish-orange color that contrasts nicely with green plants. It also has a nice woodsy smell that most people love. Of course, it also has the same benefits as other organic mulches. It helps retain soil moisture, it inhibits weed growth, and it helps to insulate the soil and regulate the soil temperature. Cedar is also a long lasting mulch because the oils act as a natural wood preservative. It can last for 3-4 years. In addition, cedar is an organic material. This makes it more environmentally friendly than inorganic mulch like rubber. Cedar is one of the best types of mulch for these reasons. 

For more in-depth info, check out my guide to the pros and cons of cedar mulch.

Do you use cedar mulch to repel pests in your yard? Share your experience in the comments below!

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How to Use Cedar Mulch To Repel Bugs and Other Pests

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