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Gardeners hear over and over again that they need to cover their soil. But with the abundance of soil mulches to choose from, how do you know what is best for your specific soils and crops? Between cedar mulch, pine mulch, and other wood based mulch mixes, it can be confusing to know what to pick.
Cedar mulch is a popular option that is widely available and fairly affordable. It can help regulate the soil temperature, improve moisture retention, suppress weeds, repel pests, and improve the aesthetic of your garden. However, it has some notable specifications and drawbacks that you should be aware of.
Let’s dig into everything you need to know about using cedar mulch in your garden, and if you should be looking at alternatives instead.
The Short Answer
Cedar mulch is an incredible asset to most gardeners because it takes years to break down. However, it’s best to keep it out of your annual vegetable beds. This carbon-rich material isn’t dangerous to vegetables, but it could “rob” them of nitrogen and make it harder to maintain adequate fertility levels. It also isn’t good for boggy soil or plants that resent too much moisture.
Instead, use cedar mulch to suppress weeds, conserve moisture, and repel pests in your perennial beds and pathways. This aromatic wood mulch has a slightly acidic effect that can be great for many perennial ornamentals and trees. It even repels ants and other pests with its pleasant scent. Finely shredded cedar mulch can be great for compost or for an aesthetically-pleasing border.
The Long Answer
Cedar mulch is a fragrant wood bark from trees in the cedar family, such as White Cedar (Thuja occidentalis), Western Red Cedar (Thuja plicata), and Eastern Red Cedar (Juniperus virginiana). These evergreen trees are commonly found in USDA zones 7 through 9.
When cedars are pruned or cut down, the wood is chipped or shredded and sold in bags or in bulk. It is most commonly used as an ornamental mulch around perennial plants.
This type of mulch is known for its longevity in the garden—it takes much longer to break down than other types of mulch. This could be due to a bacteria and fungi-resistant compound in the wood called thujaplicin.
This keeps the mulch from breaking down as quickly as leaves or deciduous wood chips. Some gardeners keep it at the base of their plants for 5 years or more without having to replace it.
However, no mulch is perfect for all applications. Cedar mulch only should be used for certain plants and has a few drawbacks that you should be aware of before you dump it on your soil.
Will it Inhibit Plant Growth?
Cedar mulch does not inhibit plant growth, but it can suppress seeds from germinating. In most cases, it will improve the growth of most plants, especially trees, woody perennials, and irrigation-thirsty crops. There is plenty of confusion about mulches killing plants.
Some myths and misinformation even claim that certain types of wood mulch are dangerous for the garden! Despite what you may hear about cedar wood chips negatively impacting your garden, there is little scientific evidence to back up this claim.
The main proven “danger” of using cedar mulch—and wood mulches in general—is the risk of reducing nitrogen availability due to their high carbon content. You can combat this by using shredded cedar bark (rather than larger wood chips) or adding additional nitrogen-rich organic matter like aged manure.
Due to its carbon-rich composition, this makes it more ideal for woody perennial plants than for nitrogen-hungry annuals. If you are concerned about this, simply avoid using it in your vegetable garden. Instead, use it in pathways and perennial beds. Use a high quality organic mulch for vegetable gardens.
Fresh cedar can have a slight acidic effect on the pH (just like any woody material), but it is usually so small that you won’t see a noticeable difference. Some gardeners have also been concerned that it releases allelopathic chemicals that make other plants not want to grow there.
Studies show that cedar does have some suppressive effects on certain weeds, which can play to your advantage. Red cedar (Juniperus silicola) can inhibit the germination of tender seeds like lettuce, so don’t sow seeds directly into mulch of any kind or you may be disappointed.
However, the allelopathic (plant-inhibiting) compounds in cedar are not much to worry about compared to plants like Black Walnut (Juglans nigra) which should never be used as mulch anyhow.
Benefits
Like all mulches, the main function of cedar mulch is to cover the soil. This benefits your garden in a plethora of ways, including:
Moisture Retention
Cedar mulch prevents the soil from drying out by protecting it from evaporating in the sun. The chipped or shredded bark acts like a moisture-retaining blanket and is especially absorbent after rain.
Moreover, the mulch prevents wind from blowing over the soil and drying it out. You can typically install drip irrigation lines or soaker hoses beneath a layer of mulch to improve the moisture-retaining effects.
Weed Suppression
Bark mulches excel at smothering weeds because they are thicker and heavier than leaf mulches. The mulch creates a physical barrier between the soil and the sun, which prevents sunlight from helping existing weed seeds to germinate.
Without light, the weeds usually die young or don’t germinate at all. Although some aggressive perennial weeds can make it through a dense layer of mulch, the cedar chips make it harder to do so.
Soil Insulation
Cedar chips or shreds act as insulation above the soil layers. It buffers the soil from heating up too much in the sun or getting too cold at night. This buffer prevents soil temperature extremes. Deep layers of mulch can even make perennials more winter-hardy in extra-cold zones.
Pest Repellant
One of the most unique qualities of cedar mulch is its aromatic fragrance. The wood of cedar trees has a distinctive smell that repels roaches, ants, mosquitoes, and other pests.
Studies show that ants avoid nesting nearby and it can even kill some species of ants thanks to the aromatic phenols and acids in the wood. It is also naturally resistant to termites and moth infestations.
Improve Soil Carbon & Nutrients
Like most organic mulches, cedar will add a carbon-rich component to your compost or soil. It has a range of plant nutrients including nitrogen, phosphorus, potassium, sulfur, carbon, and magnesium.
Fungal Food
Microorganisms (especially fungi) are proven to break down cedar mulch slowly over time, which leads to a sustainable gradual release of nutrients for your landscape plants. The result is richer soil that has a more diverse microbiome.
Although the disease-causing fungi get most of the attention, beneficial fungi are vital parts of the underground soil food web. Bark mulches act as a food for these symbiotic fungi and help them form more mycorrhizal networks to help support your plants from the roots-up.
Needless to say, cedar mulch is like a secret ingredient to happy perennial plants, weed-free pathways, and rich soil. Here is everything you know about how to use this mulch and a few precautions to take.
Uses
Cedar mulch can be both functional and aesthetic in your landscape or edible garden. You can technically use it all around your property, but the most popular uses are:
Perennial Beds
The best use for woody mulches of any type is in your perennial beds. Trees, large bushes, and small bushes benefit from the slow decay of mulch that keeps weed competition at bay. They also enjoy the added nutrients and slight insulation through weather extremes.
Thirsty Ornamentals
Cedar bark is great for ornamental plants like Lily of the Valley, iris, cattails, daylilies, ferns, and rhododendrons that prefer moist soil. The mulch holds in water and keeps these plants protected from drought.
However, the water-holding capacity of this mulch makes it a bad option for poorly drained or boggy soils because it could lead to more root rot issues. Definitely don’t use it on plants that need dry soil like lavender or rosemary.
Tree Mulch
Cedar mulch comes from a tree, so it makes sense that it is beneficial to other trees. Native forests naturally have a thick layer of decaying woody material (called the “O” horizon of the soil) sitting on the forest floor.
You can mimic this natural soil function by mulching cedar around the trunks of trees. Just be sure to leave a 3-6” gap around the base to ensure that the mulch doesn’t actually touch the tree. This prevents wet mulch from pressing up against the trunk and causing rot or disease.
Decorative Borders
Cedar mulch is a popular aesthetic option for decorative borders of the landscape. The pleasant aroma and reddish color is a beautiful accent to many homes and ornamental gardens.
Compost Ingredient
Finely shredded mulch or sawdust is an excellent carbon-rich “brown” ingredient for your compost. It can add lots of bulky material to the pile while improving aeration and retaining moisture. It is the perfect compliment to stinky nitrogen-rich ingredients like manure or rotten grass clippings.
The slow-breakdown on cedar ensures plenty of fungal food, nutrient balancing, and odor control in your compost pile. Just be sure that you’re turning it regularly once it gets hot!
Walkways Between Raised Beds
My favorite use for cedar bark mulch is as a walkway covering. This prevents muddy boots in the winter and ensures weed-free pathways during the summer. The layers of bark between your raised garden beds make your garden look tidy and welcoming.
Cedar mulch comes in several different sizes that are ideal for different uses:
- Rough-cut cedar clippings are best for mulching around trees and pathways
- Medium cedar bark mulch is ideal for perennial and ornamental beds
- Finely shredded cedar mulch and sawdust are ideal for compost and fine layers of mulch
Regardless of how you plan to use cedar mulch, spread it an even layer 1-3” thick over the top layer of your soil. I like to use a wheelbarrow or store bought bags to dump piles of mulch every few feet, then use a rake to smooth it over the surface of each bed.
Where Should You Avoid Using it?
Cedar mulch is not a one-size-fits-all garden amendment. While it won’t harm your garden, it is recommended to keep it out of certain areas for best results. Avoid mulching with cedar in:
Annual Vegetable Beds
Most veggies require a fluffy, loamy soil with plenty of available nitrogen. They are also flipped fairly quickly, which means you are digging around in these beds and replanting them throughout the year.
Because it takes so long to break down, it can be too “heavy” for use in annual crop beds. It also is known to “lock up” nitrogen due to its high-carbon composition. If you must use it in annual beds, be sure there is ample organic matter such as nitrogen-rich compost, rotted manure, or grass clippings.
Poorly Drained Soil
Mulch is great for conserving water, but it can actually make boggy soils worse. Don’t mulch over poorly drained soil or you could cause the area to become even more anaerobic, compacted, and waterlogged.
Plants Prone to Root Rot
Cedar mulch’s excellent water retention qualities make it a liability for plants that can easily rot. The wood holds rain and irrigation for a long period of time, making it difficult for the soil to dry out. Don’t put it near Mediterranean plants, drought-loving shrubs, or desert perennials. You should particularly keep it away from rock-garden species like succulents, cacti, and aloe.
Low-lying Areas
If rainwater pools up in a certain area of the garden, cedar mulch can worsen the issue. The mulch will probably never dry out, which could attract pathogens and diseases. This is often linked to the same poor drainage and waterlogging issues described above.
When in doubt, keep it confined to pathways. It will serve its best purpose as a dry walking surface that suppresses weeds.
Pros of Cedar Mulch
- Reduces evaporation from the soil
- Suppresses weed growth
- Reduces erosion
- Buffers soil temperature
- Repels insects with aroma
- Smells nice
- Attractive reddish-brown color
- Clean, tidy aesthetic
- Lasts for years
- Wide range of uses
- Keeps pathways clean and mud-free
- Protects tree roots
- Enriches soil over time
Cons of Cedar Mulch
- More expensive
- Strong smell
- May “lock up” nitrogen availability
- Can slightly acidify soil
- Prevents seeds from germinating
- May repel some beneficial insects
- Bad for boggy or waterlogged soil
- Bad for plants prone to root rot
- Can cause disease or moisture issues
Final Thoughts
Both science and anecdotal evidence show that cedar mulch is an amazing organic amendment for your garden soil. The soil moisture and temperature regulation properties help prevent water stress and buffer against extreme weather. It is especially beneficial for trees, perennial shrubs, and pathways. It excels at smothering weeds and keeping pests at bay!
However, we advise against using cedar mulch in your annual vegetable beds because it takes years to break down and may reduce nitrogen availability to your crops.
