Cedar chips are a widely available and aromatic form of organic mulch, often derived from species like Western Red Cedar (Thuja plicata) or Eastern Red Cedar (Juniperus virginiana). This material is a byproduct of the timber industry, providing a reddish-brown, natural option for landscape beds. Cedar chips conserve moisture, moderate soil temperature, and suppress weeds. Understanding its unique properties is key to maximizing its benefits for plant and soil health.
Suitability and Primary Functions
A primary reason for choosing cedar chips is their exceptional longevity compared to other organic mulches. The wood contains natural compounds, such as thujaplicin, which resist decay from fungi and bacteria. This slow rate of decomposition means the mulch layer remains intact for a longer period, reducing the frequency of reapplication.
The distinctive, pleasant aroma of cedar is due to volatile organic compounds (VOCs) that serve as natural deterrents to certain pests. These oils can inhibit or repel common garden nuisances like moths, termites, and some species of ants. This provides a measure of pest control without the need for chemical treatments in the mulched area.
Cedar chips are effective at regulating soil conditions. The layer of chips acts as an insulator, keeping the soil cooler during hot summer months and warmer when temperatures drop. This helps maintain a stable soil temperature, which is beneficial for root development. Furthermore, the physical barrier reduces water evaporation from the soil surface, conserving moisture and decreasing the need for frequent watering.
Specific Impact on Soil and Plants
The woody nature of cedar chips introduces two primary considerations for soil health: nitrogen immobilization and allelopathy. Wood materials have a high Carbon-to-Nitrogen (C:N) ratio, meaning the microorganisms responsible for breaking them down require more nitrogen than the material provides. To complete the decomposition process, these microbes temporarily draw available nitrogen from the surrounding soil.
This process, known as nitrogen tie-up, primarily affects the uppermost layer of the soil. While this localized nitrogen deficiency often helps suppress the germination of weed seeds, it can temporarily starve the roots of shallow-rooted plants or delicate annuals. For plants with deeper, more established root systems, the effect is minimal, as their roots extend below this zone of nitrogen depletion.
Another element is allelopathy, where cedar wood contains compounds that can leach into the soil, potentially suppressing the germination of sensitive seeds or inhibiting the growth of young seedlings. This effect is often overstated for aged or weathered cedar mulch. The physical smothering by a thick mulch layer is often a greater inhibitor of plant growth than the chemical effect.
Proper Application and Usage Scenarios
To maximize the benefits of cedar chips while mitigating potential drawbacks, proper application is necessary. The mulch should be applied in an even layer with a maximum depth of two to three inches. Applying more than four inches can restrict the flow of water and air to the soil, potentially leading to excess moisture and root issues.
It is particularly important to avoid creating a “mulch volcano,” where the material is piled directly against the base of a plant or tree trunk. Mulch should be pulled back, leaving a gap of several inches around the stem or trunk. This allows for proper air circulation and prevents moisture from causing rot or attracting pests.
Placing cedar chips around established trees, shrubs, and perennial beds is the most suitable use, as these plants are less susceptible to surface-level nitrogen tie-up. Cedar chips are also an excellent choice for pathways and areas where plant growth is not desired, utilizing the material’s longevity and pest-deterrent properties. If the mulch is used near heavy-feeding plants, a nitrogen-rich fertilizer or compost can be applied beforehand to offset nitrogen immobilization.