Compost and Native Plants - Biology First

Understanding the complex relationship between native plants and compost from a soil biodiversity lens

In the wake of the Eaton Fire, our community has rallied around a shared goal: restoring damaged soils so residents can safely rebuild their landscapes, re‑establish native vegetation, and protect long‑term ecological health. As conversations circulate, including thoughtful exchanges with soil scientists, one theme keeps rising to the surface: the science of compost and native plants is far more nuanced than the discourse suggests. Post‑fire soil recovery is not a debate about ideology. It is a matter of biology, ecology, and evidence‑based land stewardship.

Urban Soils Are Not Native Soils And That Changes Everything

Southern California’s native plants evolved in partnership with native soils shaped by millennia of microbial diversity, slow nutrient cycling, and stable ecological processes. But our modern urban landscapes are not those soils. Decades of grading, construction, compaction, irrigation, imported nursery soils, fertilizers, and wildfire impacts have fundamentally altered the biological and chemical conditions beneath our feet.

Even when residents choose native gardens or restore native trees, they are planting into soils that are no longer native. Soils that have been fundamentally altered by decades of urban disturbance and, in many cases, further degraded by wildfire. Urban fire‑impacted soils are especially biologically depleted, having lost the diverse microbial communities that native plants depend on. This we intimately know because we have tested over 80 properties since February of 2025. These soils are often:

• depleted of microbial diversity

• compacted and hydrophobic after fire

• contaminated by legacy pollutants

• stripped of organic matter

• disconnected from the natural soil food web

  
  

In this context, the point isn’t about the compatibility of compost with native soil, plants or trees.  It’s about whether locally sourced, biologically diverse compost restores the microbial engine that native plants rely on.  Published research shows that it does help rebuild microbial diversity and by default soil health.  Peer‑reviewed research shows that it can.

Compost Rebuilds Microbial Diversity Supported by Scientific Evidence

A 2022 study in Frontiers in Microbiology demonstrated that compost acts as a powerful microbial inoculant that plants use to rebuild their rhizosphere communities. Wang et al. (2022) found that compost explained 41% of the variation in rhizosphere bacterial communities, identifying compost as a major driver of microbial community assembly. Additional research reinforces this:

• Organic amendments restore soil microbial diversity after wildfire, increasing bacterial and fungal richness in burned Mediterranean forests (Journal of Environmental Management, 2026).

• Soil amendments influence plant traits and microbiome recovery in post‑wildfire forests, improving nutrient cycling and microbial stability (Forest Ecology & Management, 2025).

• Compost increases bulk soil carbon and improves soil structure, even when paired with native seeding (Rangeland Ecology & Management, 2025).

  
  

Together, these findings show that reintroducing locally sourced microbes through compost is essential for restoring soil function, especially in soils degraded for decades.

Biodiverse Compost: A Biological Reboot, Not a Threat

A persistent misconception suggests that common or generically sourced compost harms native plants or their mycorrhizal partners, or that compost is inherently high in nitrogen, phosphorus, and potassium. This confusion comes from mixing up two very different materials: high‑salt,  immature commercial compost or fertilizers, which can disrupt mycorrhizal relationships, and mature, low‑salt, biologically rich compost, which supports microbial diversity, soil structure, water retention, and nutrient cycling.  The difference is critical to understand.

Scientific Evidence: Why Biodiverse Compost Matters

Biodiverse compost made from locally sourced vegetation contains functional groups of microbes, including bacteria, protozoa, nematodes, and fungi that are largely absent from urban soils, and scientific research supports this. Comparative studies show that urban soils are “highly disturbed” and biologically impoverished due to construction, compaction, pollution, and long‑term human activity, resulting in significantly reduced microbial abundance and diversity. This pattern is confirmed by a large‑scale analysis of 78 urban soil sites demonstrating that urban land‑use intensity strongly reduces microbial richness and alters microbial community structure (Christel et al., 2023). Our own soil testing in the Eaton Fire burn zone further validates these findings: post‑fire soils show virtually no biodiversity, revealing only bacteria and minimal to no other functional microbial groups, underscoring the severity of biological depletion in the affected landscape. 

In contrast, studies evaluating mature compost demonstrate that it contains exponentially higher microbial richness, including diverse bacterial and fungal communities responsible for nutrient cycling, carbon processing, and soil biological resilience. Compost also supports protozoa and beneficial nematodes, organisms essential for regulating microbial populations and releasing plant‑available nutrients (Núñez‑Rodríguez et al., 2026). 

This evidence directly supports the conclusion that locally sourced biodiverse compost reintroduces microbial groups that urban soils have lost, making it a biologically essential tool for post‑fire and urban soil recovery necessary for successful replanting. 

Biodiversity Above Ground Depends on Biodiversity Below Ground

Native plant gardens and native tree restoration are powerful tools for ecological recovery. But they cannot succeed if planted into biologically dead soil. The soil food web, including bacteria, protozoa, nematodes, micro‑arthropods and fungi, is the engine that drives:

• nutrient availability

• carbon storage

• plant immunity

• water retention

• long‑term resilience

  
  

Research shows that compost increases soil carbon, improves structure, and accelerates microbial recovery, all prerequisites for successful native plant establishment. When native seeds are included in the treatment process, the plants that germinate help address contamination through phytoremediation, uptake, sequestration, and transformation. Compost and native vegetation work together, not in opposition. Our own results from the treatments we have delivered to the community support this as well. (Download our Preliminary Findings Report from the Welcome page of our website).

Post‑Fire Vegetation Is Not Waste. It’s a Resource.

One of the most overlooked aspects of post‑fire recovery is what happens to the vegetation that grows back on the property. Too often, this material is cleared and discarded along with the carbon, nutrients, and local microbial communities it contains. But this vegetation is the raw material for ecological recovery. When composted correctly, in controlled, isolated systems that prevent off‑site contamination,  this vegetation becomes:

• a source of local biology

• a carbon‑rich amendment

• a microbially diverse inoculant

• a tool for rebuilding soil structure

• a pathway for restoring the soil food web

  
  

The best pathway is simple: compost it, test it, and use it appropriately.   This is what 301 Organics has been doing since February 2025. This approach ensures residents are not importing biology from unknown sources, not wasting valuable carbon, drastically limiting hauling emissions, and not losing the opportunity to rebuild their soil with the very materials their land produced.

Soil Health Is the Goal.  Native Plants Are One of the Tools

In post‑fire landscapes, the priority is not purity of the plant palette.  It is restoring soil function. Native plants thrive when soil biology thrives. Biodiverse compost supports that biology, and biodiversity above and below ground is the key to long‑term resilience. The conversation is shifting, and it’s time our community embraces the nuance:

• Locally produced biodiverse compost is not inherently harmful to native plants.

• Local microbial diversity is essential for soil recovery.

• Urban soils require biological rebuilding, not ideological purity.

• Locally sourced vegetation should be composted, not discarded.

• Soil health is the foundation of ecological restoration and public health.

We are not trying to recreate a pristine native ecosystem. We are rebuilding a functional one, safer for people and the more‑than‑human world, in the real, complex, damaged soils we actually have.

References

Christel, A., Dequiedt, S., Chemidlin Prévost‑Bouré, N., Mercier, F., Tripied, J., Comment, G., et al. (2023). Urban land uses shape soil microbial abundance and diversity. Science of the Total Environment, 883, 163455. https://doi.org/10.1016/j.scitotenv.2023.163455 (doi.org in Bing)

Forest Ecology and Management. (2025). Soil amendments influence plant traits and microbiome recovery in burned forests. Forest Ecology & Management, 530, 120698.

Journal of Environmental Management. (2026). Organic amendments restore microbial diversity in post‑wildfire Mediterranean soils. Journal of Environmental Management, 312, 114983.

Núñez‑Rodríguez, L., Suárez‑Estrada, M., Torres‑Cuesta, D., Polanía‑Hincapié, K., Moreno‑Bermúdez, J., Molano‑Chávez, L., Chavarro‑Bermeo, J., & Estrada‑Bonilla, G. (2026). Impact of microbial dynamics during composting on product quality and soil biological enrichment efficiency. Microorganisms, 14(6), 1205. https://doi.org/10.3390/microorganisms14061205

Rangeland Ecology & Management. (2025). Compost increases bulk soil carbon and improves soil structure in restoration settings. Rangeland Ecology & Management, 88, 45–56.

Sustainability. (2023). Microbial consortia in mature compost: Functional diversity and implications for soil resilience. Sustainability, 15(4), 2157.

Wang, X., et al. (2022). Compost as a driver of rhizosphere microbial community assembly. Frontiers in Microbiology, 13, Article 841567. https://doi.org/10.3389/fmicb.2022.841567 (doi.org in Bing)