Can You Compost Cedar Chips? Breaking Down the Garden Controversy (Ultimate Guide)

Introduction: The Cedar Composting Dilemma

You've just finished a garden project using cedar chips, and now you're staring at a pile of leftovers. The responsible gardener in you wants to compost them, but you've heard conflicting advice. Some gardening friends swear cedar kills compost microbes, while others claim they've successfully composted cedar for years.

This confusion is understandable. Cedar contains natural oils and compounds like thujone that give it those desirable rot-resistant properties we love for outdoor furniture and garden beds. However, these same properties make cedar a challenging material to compost effectively.

In this comprehensive guide, you'll discover exactly how to determine if your cedar chips can be safely composted, what alternatives exist if they can't, and how to make the best decision for your specific garden situation. No more guesswork or wasted resources.

By the time you finish reading, you'll have a practical 3-step decision framework for handling cedar waste sustainably—whether you're working with a small urban compost bin or managing a larger homestead system. Let's transform this garden controversy into a clear path forward.

Quick Reference Guide: Cedar Chips Composting Basics

Material Properties:

Decomposition Rate: Very slow (4-6 times longer than other wood chips)
Carbon-to-Nitrogen Ratio: Approximately 350:1 (extremely carbon-heavy)
pH Impact: Mildly acidic (4.5-5.5)
Contains: Thujone, thujaplicins, and other natural preservative compounds

Benefits When Properly Composted:

Adds long-term structural elements to finished compost
Creates air pockets that improve compost aeration
Provides slow-release carbon source over multiple seasons
Imparts natural fungal resistance to finished compost

Maximum Recommended Amount: 10% of total compost volume

Why Cedar Chips Challenge Traditional Composting Methods

The resistance cedar shows to decomposition isn't random—it's chemistry at work. Cedar contains natural preservatives, primarily thujone and thujaplicins, which have evolved specifically to protect the tree from decay. These compounds effectively repel insects, resist fungal growth, and slow bacterial action—all processes essential to successful composting.

In simple terms, cedar has allelopathic properties—it releases biochemicals that influence (often inhibit) the growth and development of other organisms. Think of it as cedar's natural defense system. While this makes cedar excellent for outdoor furniture, it creates challenges in your compost pile where you're actively trying to encourage decomposition.

The decomposition timeline tells the story clearly: while standard hardwood chips might break down in 6-12 months under good conditions, cedar chips typically take 2-4 years to fully decompose. That's 4-6 times longer! This extended timeline can disrupt your composting rhythm, especially if you're counting on finished compost for seasonal garden applications.

The pH factor also matters, though perhaps less than many gardeners fear. Fresh cedar chips typically measure between 4.5-5.5 on the pH scale (with 7 being neutral). While this is indeed acidic, it's not dramatically different from pine needles (pH 3.5-4.5) that many gardeners successfully compost. The key difference is that cedar's oils slow the neutralizing processes that would normally balance this acidity over time.

Furthermore, the extremely high carbon-to-nitrogen ratio of cedar (approximately 350:1) creates an additional challenge. Effective composting typically requires a C:N ratio closer to 30:1, meaning cedar chips need significant nitrogen-rich materials to balance them out—far more than most gardeners anticipate.

Cedar Composting: 5 Myths vs. Science-Backed Facts

Myth #1: "Cedar chips completely kill beneficial compost microbes"
Fact: Research shows cedar compounds inhibit rather than eliminate microbial activity. Studies from Washington State University found that while fresh cedar can reduce microbial populations by 30-60%, it doesn't create a sterile environment. Additionally, certain fungi and bacteria actually adapt to cedar's compounds over time. The key is concentration—small amounts of cedar introduce manageable stress to the microbial ecosystem.

Myth #2: "Cedar chips make compost too acidic for plants"
Fact: While fresh cedar chips are indeed acidic (pH 4.5-5.5), their impact on overall compost pH is typically minimal when properly balanced. Laboratory measurements of finished compost containing 10% cedar showed final pH readings between 6.2-7.0—well within the ideal range for most plants. The composting process itself neutralizes much of cedar's initial acidity as microorganisms break down the material.

Myth #3: "All cedar species affect compost equally"
Fact: The concentration of inhibitory compounds varies significantly between cedar species. Western Red Cedar (Thuja plicata) contains the highest levels of thujone and is most challenging to compost. Eastern Red Cedar (Juniperus virginiana) and White Cedar (Thuja occidentalis) contain fewer oils and decompose more readily. Knowing which species you're working with helps set realistic expectations.

Concentration matters: Adding 10% cedar chips to your compost creates a manageable challenge for the decomposition process. However, when cedar exceeds 50% of your compost volume, the concentration of inhibitory compounds often overwhelms the system's ability to adapt. This is why many gardeners report both success and failure with cedar—the percentage makes all the difference.

The weathering effect: Time naturally neutralizes cedar's challenging compounds. Research from Oregon State University demonstrated that cedar chips weathered outdoors for 9-12 months lost approximately 60-70% of their thujone content. This explains why older cedar mulch eventually decomposes despite initial resistance. Nature has already begun breaking down the compounds that once protected the wood.

6 Proven Methods for Successfully Composting Cedar

1. The 10% Rule
Keep cedar chips below one-tenth of your total compost volume. This simple ratio ensures the concentration of inhibitory compounds remains low enough for microorganisms to adapt and thrive. In practical terms, for every 5-gallon bucket of cedar chips, add at least 45 gallons of other compostable materials. This dilution strategy is particularly important for smaller compost systems with less microbial diversity.

2. Pre-weathering Technique
Age your cedar chips for 3-6 months before adding them to your compost pile. Simply spread them in a thin layer (about 2 inches deep) in an out-of-the-way garden area exposed to rain and sun. Turn the pile once monthly. This pre-weathering process allows natural elements to begin breaking down the oils and resins that inhibit decomposition. The chips will fade from bright reddish tones to a silvery gray when they're ready for composting.

3. Hot Composting Strategy
Maintain your compost at temperatures between 130-150°F for extended periods to break down cedar's resistant compounds. This requires a compost pile at least 3 feet in all dimensions and regular turning to maintain aerobic conditions. The elevated temperatures accelerate the breakdown of thujone and other preservative compounds. A compost thermometer is essential for monitoring this process effectively.

4. The Microbial Boost
Add compost accelerators specifically designed to introduce microorganisms that can handle challenging materials. Products containing fungi from the Phanerochaete chrysosporium family are particularly effective with cedar, as these white-rot fungi have evolved to break down similar compounds in nature. Alternatively, add a shovelful of rich woodland soil, which naturally contains diverse decomposer organisms adapted to breaking down forest materials.

5. Proper Carbon/Nitrogen Balancing
Offset cedar's extremely high carbon content by maintaining a 3:1 ratio of nitrogen-rich materials to cedar chips. Practical nitrogen sources include fresh grass clippings, vegetable scraps, coffee grounds, or aged manure. This intentional balancing act provides the necessary nutrients for microorganisms to effectively tackle cedar's resistant structure.

6. Chopping Technique
Reduce cedar pieces to under ½ inch in size to dramatically increase decomposition rates. Smaller pieces expose more surface area to microbial activity, allowing decomposers to work more efficiently. Studies show that cedar chips reduced to this size decompose up to 70% faster than larger pieces. A chipper/shredder is ideal, but even manual chopping with pruners or running over chips with a lawn mower helps significantly.

When to Avoid Adding Cedar to Your Compost Pile

Despite the methods above, there are situations where composting cedar simply isn't the best option. Watch for these warning signs that your seedlings may not tolerate cedar-containing compost:

Stunted growth within 7-10 days of application
Yellowing leaves, particularly on new growth
Delayed germination compared to control groups
Wilting despite adequate moisture

The volume problem becomes critical when cedar exceeds 15% of your compost content. At this concentration, even with proper management, the inhibitory effects often overwhelm the beneficial aspects of composting. If you find yourself with excess cedar chips, consider these four alternative disposal methods:

Municipal green waste programs (many have specialized processing for woody materials)
Offering to landscape companies that combine various materials
Forest trail maintenance projects (many parks accept natural wood chips)
Gradual application as mulch in established ornamental beds (avoid vegetable gardens)

You can recognize if cedar is overwhelming your compost through these visual indicators:

Distinct layers remain visible after 3+ months (lack of integration)
Cedar chips show minimal change in color or texture over time
White fungal growth is absent from cedar pieces (indicates resistance to decomposition)

For a quick assessment, try this simple 5-minute jar test: Place a handful of your cedar chips in a jar with moist compost, seal it, and check for odor after 5 days. A sweet, earthy smell indicates decomposition is possible; a strong cedar smell suggests the chips are still too fresh to compost effectively.

7 Better Uses for Cedar Chips in Your Garden

Instead of struggling to compost cedar chips, consider these more appropriate applications that leverage cedar's natural properties:

1. Strategic Mulching
Cedar chips excel as a 2-3" protective layer around established perennials, shrubs, and trees (avoiding vegetable gardens). Their slow decomposition rate means you'll need to replenish much less frequently than with other mulches—typically every 2-3 years rather than annually. Apply in early spring after soil has warmed to avoid insulating cold winter soil temperatures.

2. Natural Pest Control
Utilize cedar's repellent properties by placing chips strategically to deter specific garden pests. A 2" band of cedar chips creates an effective barrier against slugs, snails, and many crawling insects. Cedar is particularly effective against moths that lay eggs at the base of cabbage family plants and certain ant species that farm aphids.

3. Durable Garden Pathways
Create long-lasting garden paths by laying down 3-4" of cedar chips over landscape fabric. These pathways typically last 3-5 years with minimal maintenance, compared to 1-2 years for hardwood mulch paths. The natural oils prevent compaction during wet periods and minimize weed germination. Add a fresh 1" layer annually to maintain appearance.

4. Decorative Applications
Leverage cedar's rich color and texture in purely decorative garden areas where decomposition isn't the goal. Cedar makes excellent top-dressing for container plants (especially those that prefer acidic conditions) and creates attractive borders between garden sections. The natural color lasts 1-2 years before weathering to silver-gray.

5. Cedar-Compatible Planting
Some plants actually thrive with cedar mulch, including:

Rhododendrons and azaleas
Blueberries and cranberries
Conifers and pine trees
Heathers and heaths
Camellias

These acid-loving plants benefit from cedar's slight pH reduction and appreciate the fungal resistance it provides.

6. Cedar Chip Tea
Create a gentle pest deterrent spray by steeping 2 cups of cedar chips in 1 gallon of water for 24-48 hours. Strain and use this "tea" as a foliar spray to deter soft-bodied insects like aphids and whiteflies. Test on a small area first, as some plants may be sensitive to cedar compounds.

7. Blended Mulch Mixes
Combine cedar with other materials to create balanced, long-lasting mulch mixes. A mixture of 30% cedar chips, 50% hardwood chips, and 20% compost creates an ideal balance of durability and soil-building properties. This approach dilutes cedar's inhibitory effects while benefiting from its longevity and pest-repellent qualities.

Your 3-Step Cedar Chip Action Plan

Use this decision framework to determine whether to compost, repurpose, or dispose of your cedar chips:

Step 1: Assess Your Cedar

Fresh, aromatic chips with strong color → Repurpose or pre-weather
Aged, gray chips with minimal scent → Potential for composting
Treated or stained cedar → Dispose responsibly (never compost)

Step 2: Evaluate Your Needs

Need for immediate compost → Choose alternative methods
Long-term soil building → Limited composting possible
Mulch or pathway needs → Direct application is ideal

Step 3: Match Method to Volume

Small amount (less than 5 gallons) → Incorporate into existing compost at 10%
Medium amount (5-20 gallons) → Weathering followed by gradual composting
Large amount (20+ gallons) → Repurpose for pathways and mulch

If composting: Prepare your cedar chips in just 15 minutes by:

Chop or shred to smaller pieces
Soak in water for 10 minutes to begin leaching oils
Mix with twice the volume of nitrogen-rich materials
Add a shovelful of finished compost as a microbial starter
Incorporate into your compost pile in thin layers

If repurposing: Quick-start with these immediate applications:

Apply as mulch around acid-loving ornamentals
Create a 2" protective barrier around tree bases
Establish a temporary garden path by laying directly over cardboard

If disposing: Choose environmentally responsible options that take less than 30 minutes:

List on community sharing platforms (Freecycle, Facebook groups)
Contact local landscapers who may combine with other materials
Check with municipal waste services about woody waste programs

Timeline expectations:

In 2 weeks: Cedar in compost will show minimal change
In 1 month: Weathering cedar will begin losing its reddish color
In 6 months: Properly managed cedar in compost will show signs of fungal colonization

Sustainable Cedar Management: Your Takeaway Plan

The key to successfully managing cedar in your garden comes down to matching the right approach to your specific situation. Cedar can be composted, but only when you respect its natural properties and work with them rather than against them.

From an environmental perspective, finding appropriate uses for cedar within your garden reduces your carbon footprint significantly compared to disposal. Each cubic yard of cedar chips repurposed rather than sent to landfill prevents approximately 242 pounds of CO2 equivalent emissions.

This approach connects to broader garden sustainability practices—working with natural materials according to their inherent properties rather than forcing them into unsuitable roles. Just as we select plants appropriate to our climate and soil conditions, we must match our management of garden materials to their unique characteristics.

Your next steps this weekend:

Sort any cedar chips you currently have by age and condition
Set aside the freshest 10% for composting (if desired)
Designate appropriate garden areas for direct application of the remainder
Begin a small test batch using the methods outlined above

Remember that sustainable gardening isn't about perfect solutions but about making informed choices that work within natural systems.

FAQ: Common Cedar Composting Questions Answered

How long does it take for cedar chips to fully decompose in compost?
Under ideal conditions with proper management, cedar chips smaller than ½ inch may decompose in 12-18 months. Larger pieces typically take 2-4 years. Without active management, cedar can persist for 5+ years in a compost pile.

Will cedar chips make my compost too acidic for vegetable gardens?
When limited to 10% of total volume, cedar chips have minimal impact on finished compost pH. The composting process itself neutralizes much of the initial acidity. If concerned, test your finished compost with an inexpensive pH meter before application.

Can I use cedar-containing compost around seedlings safely?
For sensitive seedlings, age cedar-containing compost an extra 2-3 months before use, or limit it to 25% of your seedling mix. Established plants typically show no negative effects from properly composted cedar.

What should I do if I've already added too much cedar to my compost?
Add high-nitrogen materials like fresh grass clippings, coffee grounds, or aged manure to balance the carbon load. Introduce finished compost as a microbial starter, and turn the pile more frequently to encourage aeration and heating.

Does cedar mulch attract or repel termites and other insects?
Fresh cedar chips actively repel many insects, including termites. However, as cedar ages and its oils break down (typically after 2-3 years), this repellent effect diminishes. Cedar is not a long-term termite solution, but it does provide temporary deterrence.

Can I compost cedar that's been treated or stained?
No. Treated cedar (pressure-treated or chemically preserved) should never be composted as it may contain toxic compounds that can contaminate your compost and garden. Similarly, stained or painted cedar should be disposed of according to local regulations for treated wood.