When it comes to landscaping and garden maintenance, choosing the right mulch can significantly impact your outdoor space's health, appearance, and maintenance requirements.
Two popular options dominate the market:
- traditional wood mulch
- the increasingly prevalent rubber mulch.
But is rubber mulch better than wood mulch?
The answer depends on your specific needs, priorities, and the application you have in mind.
What is Wood Mulch?
Wood mulch consists of organic materials derived from trees, including bark, branches, wood chips, and sometimes leaves.
These materials are ground, shredded, or chipped into various sizes and textures.
Wood mulch decomposes naturally over time, providing nutrients to the soil and supporting beneficial microorganisms.
What is Rubber Mulch?
Rubber mulch is manufactured from recycled rubber, most often sourced from waste tires.
The manufacturing process involves shredding or grinding old tires from cars, trucks, and bicycles; removing steel bands; and creating uniform pieces that resemble traditional wood mulch.
While this repurposes waste materials, concerns exist about the environmental and health impacts of using tire-derived products in landscapes.
Environmental Impact of Rubber Mulch and Wood Mulch
Soil Health and Nutrient Enrichment
The most significant difference between these two mulch types lies in their impact on soil health.
Research has consistently proved that wood mulch improves soil quality through multiple mechanisms.
A study by Scharenbroch and Watson (2014) found that wood chips significantly improved soil organic matter, loosened compacted soil, maintained moisture levels, and slowly added nutrients over time.
The research confirmed that wood chip mulch does not rob soil of nitrogen, contrary to popular belief, and actually increases nitrogen levels even above those achieved with synthetic fertilizer alone.
In contrast, rubber mulch provides no nutritional value to soil. Chalker-Scott (2007) concluded in her comprehensive review that rubber mulches have not proved to be particularly good choices for either horticultural production or landscape uses.
Additionally, other studies comparing various mulch types found rubber tire mulch less effective in controlling weeds in herbaceous perennial plots than wood chips.
Chemical Leaching Concerns
One of the primary concerns surrounding rubber mulch is its potential to release chemical constituents into the surrounding environment.
Laboratory analyses have shown that shredded rubber mulch can leach metals and other compounds when exposed to water, raising questions about its suitability in applications where runoff or soil contact is expected.
A controlled laboratory study by Kanematsu et al. (2009) evaluated leachates from shredded rubber mulch to determine whether its use in stormwater best management practices could pose water-quality risks.
Using batch leaching tests, the researchers compared rubber mulch with conventional wood mulch and analyzed the resulting aqueous extracts for metals, nutrients, total organic carbon, and biological activity across a range of pH levels and temperatures.
The study found that rubber mulch released markedly higher concentrations of zinc into water than wood mulch, presenting differences in leaching behavior between the two materials.
Measured zinc concentrations in rubber mulch extracts ranged from approximately 2,000 to 28,000 μg/L, which was 40 to 200 times higher than concentrations observed in leachates from wood mulch under comparable conditions (Kanematsu et al., 2009).
The authors further note that zinc accounts for roughly 1% of tire mass, providing a plausible explanation for these elevated levels.
Zinc release was greater at lower pH and higher temperatures, conditions that can occur in certain stormwater environments.
While the study itself did not directly evaluate ecological harm, it cited existing research indicating that elevated zinc concentrations are known to cause toxic effects in aquatic organisms.
Durability and Maintenance of Rubber Mulch and Wood Mulch
Longevity
Rubber mulch excels in durability, lasting many years without significant breakdown. Wood mulch, on the other hand, requires replacement for at least in every one to four years depending on the type (Greenly & Rakow, 1995).
However, this characteristic of wood mulch is actually beneficial for soil health, as each application adds fresh organic matter, continually feeding and improving the soil structure.
Maintenance Requirements
Rubber mulch is denser and stays in place longer due to its weight. Wood mulch, being lighter, may require periodic redistribution, especially in high-traffic areas.
Temperature and Climate Factors
Heat Retention
Rubber mulch absorbs and retains significantly more heat than wood mulch. Research measuring surface temperatures found that rubber mulch beds can produce problematic heat levels.
In testing conducted by the University of Nevada Cooperative Extension, shredded rubber burned at temperatures exceeding 630 degrees Fahrenheit at a height of four inches (Quarles & Smith, 2007).
Water Management
Research has demonstrated that wood mulch significantly improves water retention. A study on mulch effects found that moisture levels increased substantially with wood chip application (Greenly & Rakow, 1995).
Consequently, multiple studies have also confirmed these benefits. Research on agricultural mulching demonstrated that organic mulches conserve soil moisture and maintain optimal soil temperature, providing beautification while improving growth and yield of various crop plants (Kader et al., 2019, as cited in Mahmood et al., 2020).
Safety and Health Considerations
Fire Hazard
When comparing fire safety, rubber mulch presents serious concerns. Multiple independent studies have evaluated the combustibility of landscape mulches with consistent findings.
The University of Nevada Cooperative Extension study found that shredded rubber mulch was among the most hazardous mulches tested (Quarles & Smith, 2007).
Rubber burned at the hottest average temperature and produced the greatest flame length at over three feet.
According to findings reported in multiple fire safety assessments, rubber mulch fires cannot be extinguished with water—water actually spreads the flames faster—and the material produces toxic fumes when burning (Quarles & Smith, 2007).
The Marin Wildfire Prevention Authority funded study confirmed these findings, noting that shredded rubber burned at temperatures exceeding 630°F with flame heights over three feet.
In contrast, composted wood chips demonstrated the slowest fire spread rate of all mulches tested, usually producing only smoldering combustion with minimal flaming (Quarles & Smith, 2007). Wood mulch burns at lower temperatures and is easier to extinguish compared to rubber alternatives.
Playground Applications and Health Concerns
While rubber mulch has gained popularity in playground settings due to its impact absorption properties, health concerns persist.
A study published in Scientific Reports examined metal surface release from tire crumb rubber playground tiles through accelerated weathering (Zhu et al., 2023).
The research found that cumulative release of copper, arsenic, thallium, and antimony reached potentially harmful levels at various times within three years of simulated aging.
The EPA has launched research initiatives to study potential human health effects of recycled tire crumb, particularly regarding children's exposure on playgrounds. While some testing has found VOC levels to be generally low, long-term health implications remain under investigation.
Pest and Weed Control
Weed Suppression
Both mulch types suppress weeds when applied at adequate depths, though research shows wood mulch performs better. Studies comparing different mulch materials consistently find that wood chips provide superior weed control.
Greenly and Rakow (1995) documented that mulch depth had a dramatic effect on weed populations, with deeper wood chip applications providing the most effective suppression.
Chalker-Scott's (2007) comprehensive review noted that in comparison studies, rubber tire mulch was less effective in controlling weeds in herbaceous perennial plots than wood chips.
The review also found that sawdust made a better mulch for Christmas tree production in terms of weed control, microbial biomass, and soil chemistry compared to rubber alternatives.
Best Applications for Each Type
When to Choose Wood Mulch
Wood mulch is the superior choice for:
- Garden beds and landscaping: Where soil health and plant nutrition are priorities
- Around trees and shrubs: To provide long-term soil enrichment
- Vegetable gardens: Where organic soil building is essential
- Eco-conscious landscaping: When environmental impact is a primary concern
- Water conservation areas: Where moisture retention is critical
When Rubber Mulch Might Be Appropriate
Rubber mulch may be considered for:
- High-traffic pathways: Where durability and minimal displacement are needed
- Non-planting areas: Where soil health is not a factor
However, even for these limited applications, many experts recommend alternatives. Chalker-Scott (n.d.) states clearly in her research that "it is abundantly clear from the scientific literature that rubber should not be used as a landscape amendment or mulch." The consensus among horticultural experts emphasizes that environmental, health, and soil quality concerns outweigh the practical advantages.
Making the Right Choice
When deciding between rubber and wood mulch, consider these evidence-based factors:
- For soil improvement and plant health: Research unequivocally supports wood mulch. Studies demonstrate increased organic carbon, improved soil structure, enhanced moisture retention, and nutrient enrichment.
- For environmental sustainability: Wood mulch integrates naturally into ecosystems without chemical contamination risks. Rubber mulch leaches heavy metals and toxic compounds that harm aquatic life and potentially contaminate soil.
- For fire safety: Multiple independent studies confirm that rubber mulch presents severe fire hazards, burning at extreme temperatures and producing toxic fumes. Composted wood chips show the slowest spread rates and lowest flame heights.
- For around food plants: Never use rubber mulch near edible plants due to heavy metal contamination risks. Research has documented zinc levels 40-200 times higher in rubber mulch than in wood mulch.
The Verdict
Is rubber mulch better than wood mulch?
Based on various extensive peer-reviewed research, the answer is NO for the majority of gardening and landscaping applications.
While rubber mulch offers durability and low maintenance, these advantages cannot overcome the significant environmental concerns, lack of soil enrichment, chemical leaching risks, fire hazards, and potential negative impacts on plant and ecosystem health.
Wood mulch remains the gold standard for landscape applications, supported by decades of horticultural research.
It enriches soil, supports beneficial organisms, helps manage water, moderates temperature naturally, and integrates harmoniously with the ecosystem.
Though it requires more frequent replacement, this characteristic represents a feature, not a flaw, as each application feeds the soil and improves your landscape's long-term health.
For specialized applications where durability is critical, carefully weigh rubber mulch against organic alternatives and consider the latest research on health, safety, and environmental implications.
In most cases, natural organic mulches represent the responsible, scientifically supported choice for gardens, landscapes, and the environment.
Conclusion
The scientific evidence overwhelmingly supports wood mulch over rubber mulch for most landscape applications.
Research has documented that wood mulch improves soil quality, enhances plant growth, conserves water, and supports ecosystem health without the environmental and safety risks associated with rubber alternatives.
While rubber mulch offers certain practical advantages in durability, these benefits are substantially outweighed by concerns including heavy metal leaching, aquatic toxicity, extreme fire hazards, and the absence of soil-enriching properties.
The peer-reviewed literature provides clear guidance: organic wood mulches should be the first choice for gardens, landscapes, and areas where plant health matters.
For homeowners, landscapers, and institutions making mulch decisions, the research-based recommendation is to choose wood mulch for its proven benefits and environmental compatibility.
References
Chalker-Scott, L. (2007). Impact of mulches on landscape plants and the environment—A review. Journal of Environmental Horticulture, 25(4), 239-249. doi.org
Chalker-Scott, L. (n.d.). Rubber mulch. Washington State University Extension. s3.wp.wsu.edu
Greenly, K. M., & Rakow, D. A. (1995). The effect of wood mulch type and depth on weed and tree growth and certain soil parameters. Journal of Arboriculture, 21(5), 225-232. doi.org
Gugliuzza, G., Ingrassia, F., Gristina, L., Gullo, G., Martinelli, F., & Farina, V. (2024). Organic mulching: A sustainable technique to improve soil quality. Sustainability, 16(23), 10261. doi.org
Kanematsu, M., Hayashi, A., Denison, M. S., & Young, T. M. (2009). Characterization and potential environmental risks of leachate from shredded rubber mulches. Chemosphere, 76(7), 952–958. doi.org
Mahmood, F., Khan, I., Ashraf, U., Shahzad, T., Hussain, S., Shahid, M., Abid, M., & Ullah, S. (2020). Potential agricultural and environmental benefits of mulches—A review. Bulletin of the National Research Centre, 44, 75. doi.org
Quarles, S. L., & Smith, E. (2007). The combustibility of landscape mulches. University of Nevada Cooperative Extension. firesafesdcounty.org
Scharenbroch, B. C., & Watson, G. W. (2014). Wood chips and compost improve soil quality and increase growth of Acer rubrum and Betula nigra in compacted urban soil. Arboriculture & Urban Forestry, 40(6), 319-331. doi.org
Zhu, H., Xiang, X., Li, T., Li, D., Zheng, Y., & Yan, B. (2023). Assessing children's potential exposures to harmful metals in tire crumb rubber by accelerated photodegradation weathering. Scientific Reports, 13, 13758. doi.org