In its chipped and shredded form, cedar mulch is widely used as a top dressing in gardens and parks. Whilst this wood mulch is known for its fragrance and ability to repel pests, there are some downsides to using cedar mulch.
In this article, we discuss the pros and cons of cedar mulch and explain when it’s best used.
Table of Contents
What Is Cedar Mulch?
Cedar mulch is made from the wood of cedar trees, including Eastern, Northern and Western Red cedar. Mulch can be found in the form of reddish-brown clippings or shavings with a distinct sweet-spicy smell.
When layered over topsoil, cedar much is used to increase moisture levels in the soil, prevent frost heaving, and regulate soil temperature. Organic mulches also impart nutrients to the soil as it decomposes.
As cedar trees are evergreens that are grown abundantly across the US, using this wood mulch is environmentally friendly.
Pros of Cedar Mulch
1. Cedar Mulch Deters Pests
One of the main benefits of cedar mulch is that it deters, or kills pests. This is because cedar mulch emits aromatic hydrocarbons and other natural chemicals (the main one being thujone) that act as natural pesticides.
Mice, for example, absorb these chemicals through their respiratory tract, which is irritating for their lungs, causing them to scurry away.
These chemicals also ward off termites, cockroaches, beetles, cloth-eating moths, and certain ants.
A sidenote: if you search the internet for thujone, you may find articles that suggest that cedar mulch kills plants due to the presence of thujone. This is a myth. There is no scientific evidence to back this, according to Washington State University and Master Gardeners.
2. Lasts Longer than Other Mulches
A benefit of cedar mulch over other organic mulches is that it takes much longer to break down. Cedar mulch needs replacing only every 2-3 years, compared with 1-3 months for grass clipping mulch and about 6 months-1 year for pine mulch.
This is owing to certain bacteria and mold-resistant substances it contains, which slow decay.
Additionally, cedar mulch does not require maintenance. Once added, you can largely forget it’s there!
3. Adds Nutrients to the Soil
Cedar mulch is organic, so when it eventually decomposes, it enriches the soil with nutrients. Nutrients include phosphorous, potassium, sulfur, and magnesium — the same nutrients found in fertilizers that encourage healthy and robust plant growth.
In addition to enriching the soil, decomposing cedar mulch also makes the soil soft and fluffy, which increases aeration. This allows plant roots to breathe and supports the uptake of water and nutrients in the soil.
4. Improves Moisture Retention
Using cedar mulch is an effective way to retain moisture in the soil. When you add a top layer of cedar mulch, it acts as a physical barrier between the air above and the soil underneath. This drastically lowers the rate at which water evaporates from the soil, resulting in higher moisture levels.
Additionally, the mulch also retains moisture by preventing soil from direct contact with the wind. It is no wonder that cedar mulch is popular for use in hot and dry climates, where moisture retention is a challenge.
Related: Check out this DIY raised garden bed tutorial.
5. Helps Regulate Soil Temperature
Another benefit of cedar mulch acting as a barrier between the soil and air is that it acts as insulation and ensures plants experience stable year-round soil temperatures.
In summer, the top layer of cedar mulch provides shade to the soil from the scorching sun. Additionally, it reduces evaporation rates, which also helps the soil remain cool.
In contrast, the layer of mulch keeps the soil warm in winter. It traps the heat produced by micro-organisms beneath the soil and prevents snow or cold air from getting in contact with the soil. This also prevents frost heaving.
The benefit of temperature regulation is especially useful in regions that experience extreme weather changes. It is also helpful for plants that are more sensitive to the cold, such as avocados, begonias, citrus trees, and alocaisias.
6. Cedar Mulch Inhibits Weed Growth
Finally, cedar mulch hinders weed growth by acting as a blanket over the soil. Deprived of sunlight, most weed seeds will not be capable of germinating.
Even so, some stubborn weeds may still push their way through. Luckily these can be easily spotted against the reddish-brown color of cedar mulch, ready for you to pull out.
Cons of Cedar Mulch
1. Cedar Mulch is Expensive
Cedar mulch is expensive; almost twice as expensive as other hardwood mulches. This can add up really quickly if you intend on covering a large area.
Our favorite cedar mulch goes for ~$0.09 / ounce; while other hardwood mulches are typically ~US$0.05 / ounce.
However, take into consideration that cedar mulch lasts 2-3 years whilst other organic mulches may need replacing more frequently. Also, remember that other hardwood mulches do not repel insects. The choice is yours!
2. You Might Need to Supplement Your Soil with Nitrogen
When cedar mulch begins to decompose, it draws nitrogen from the soil. As nitrogen is an essential component of chlorophyll (the substance plants use to manufacture food), this nutrient deficiency can be detrimental to plant growth.
Note, however that nitrogen depletion is confined to the topmost layer that is in contact with the mulch. If this nitrogen-deficient soil isn’t mixed with lower layers, deep-rooted plants will not be impacted.
However, if you intend on tilling your soil (like with vegetable patches), then it’s best to supplement your soil with a nitrogen-rich fertilizer, or reconsider using cedar mulch altogether.
3. Cedar Mulch Repels Good Insects
While cedar mulch helps keep troublesome pests away, it also deters good insects such as bees and ladybirds. These beneficial bugs play a variety of roles in the garden. For example, bees help pollinate, and ladybirds help control the pest population by eating aphids.
TLDR: When its Best to Use Cedar Mulch
The various pros and cons of cedar mulch mean you need to be careful when choosing where to use it. Here are several applications of cedar mulch and scenarios in which it is appropriate to use:
- In hot and dry climates — the evaporation rates are high, making the soil dry. Using cedar mulch helps retain moisture in the soil for longer periods.
- In extreme weather conditions — Cedar mulch is an insulator and helps regulate soil temperatures. Also great to use for plants that are sensitive to cold.
- To improve aesthetics — Cedar mulch suppresses the growth of ugly weeds. Additionally, the shredded wood chips add to the landscape’s visual appeal.
On the other hand, here are a handful of instances where cedar mulch may not be the best choice:
- Wet regions — Cedar mulch retains moisture, so using it in wet regions can cause the soil to become soggy. This may result in root rot and other plant problems.
- Annual flowerbeds and vegetable gardens — Both of these require tilling, which may result in the nutrient-deficient surface layer and lower layers mixing. You can still use cedar mulch but will need to supplement your soil with a nitrogen-rich fertilizer.
- In acidic soil — Wood mulches, including cedar mulch, marginally reduce soil pH when fresh. If the soil is already acidic, cedar mulch will drop its pH further.
Frequently Asked Questions
Is Cedar Mulch Harmful or Toxic to Plants?
No, cedar mulch is not harmful or toxic to plants. This is a myth — cedar trees and their mulches are not allelopathic.
When should you not use Cedar Mulch?
You should not use cedar mulch in areas where tilling is required and in wet or acidic soils. Additionally, cedar mulch is expensive, so beware if you are on a budget.
Is Cedar Mulch Better than Regular Hardwood Mulch?
In some ways, yes.
Cedar mulch decays much slower than hardwood mulch. This makes it much more long-lasting and requires less frequent replacements. Cedar mulch also repels insects, a property that hardwood lacks. Additionally, cedar mulch has a stronger ability to suppress weeds. Some people also enjoy the aesthetic look of cedar mulches over regular hardwood.
On balance, hardwood mulch is much cheaper than cedar mulch!
Is Cedar Mulch Toxic to Dogs?
Cedar mulch is not toxic to dogs — it is one of the most popular dog-friendly mulches. It won’t be harmful if your dog decides to play and take a walk on it or even nibble some of it! However, it can cause an upset tummy if ingested in large amounts.
Is Cedar Mulch Acidic?
Yes, cedar mulch is acidic in nature. Over time, it may leach minute amounts of acid into the soil as well, though the change in pH will be minor. This will not pose a problem in neutral soils but can worsen the problem in soils already acidic. You can check your soil’s pH by using this kit.
Is Cedar Mulch Good for Roses?
Yes, cedar mulch is an excellent choice for roses. It pairs wonderfully with these red flowers to give a beautiful, fluffy look while providing the benefits mentioned above. Additionally, it prevents soil erosion from the surface of the flowerbed by acting as a physical barrier.
Deborah is a plant enthusiast and founder of Gardening Collective.