Cedar trees are popular in landscapes due to their aesthetic appeal and natural resistance to decay. The term “cedar” often includes genera like Juniperus (Eastern Red Cedar) and Thuja (Western Red Cedar), which share problematic characteristics. Homeowners should understand the specific drawbacks of these species, as they can introduce challenges to personal health and property integrity. These issues range from triggering health responses and inhibiting other plant life to presenting risks of structural damage and fire.
Health Risks from Cedar Exposure
The primary health concerns related to cedar exposure stem from airborne particles, including fine pollen and wood dust, which trigger inflammatory responses. Cedar trees are prolific pollen producers, releasing fine grains that are easily inhaled during peak pollination seasons. This exposure frequently leads to allergic rhinitis, commonly known as “cedar fever,” causing symptoms such as nasal congestion, sneezing, and irritation of the eyes and throat.
Beyond seasonal allergies, the wood contains potent volatile organic compounds (VOCs) and natural chemicals that cause respiratory irritation. Western Red Cedar (Thuja plicata) is particularly associated with occupational asthma caused by inhaling its wood dust. The toxic effects are related to the wood’s chemical composition, which can also lead to contact dermatitis upon direct skin exposure. Even without woodworking, the presence of these compounds contributes to general respiratory discomfort, making the area less hospitable for those with pre-existing conditions.
Horticultural Drawbacks for Landscaping
Cedar trees introduce significant challenges to the surrounding landscape primarily through allelopathy. This process involves the release of biochemicals that inhibit the growth and germination of neighboring plants, reducing competition. Chemicals like Thujone, found in cedars, are exuded from the roots and leached from the foliage, negatively affecting other species.
This chemical inhibition suppresses the germination of seeds and the initial growth of seedlings, making it difficult to establish a diverse understory or garden bed beneath a cedar canopy. While the popular belief suggests that shed cedar needles acidify the soil, this effect is usually minimal due to decomposition. The more substantial issue is the dense accumulation of shed needles and cones, which smothers smaller plants and competes for available water and soil nutrients.
The dense growth habit and shallow, extensive root systems of many cedar species create intense competition for resources. These roots spread widely and close to the surface, monopolizing moisture and nutrients that nearby plants require. Consequently, the area surrounding a mature cedar often remains barren or supports only the hardiest plant life, resulting in a landscape monoculture. This makes successful gardening or lawn maintenance in the vicinity of a cedar a persistent effort.
Fire and Property Safety Concerns
Cedar trees pose a significant risk to property due to their high flammability and growth characteristics, making them dangerous in fire-prone regions. The fine, dense foliage and high concentration of volatile oils and resins allow the trees to ignite rapidly and burn intensely. This combination creates a substantial fuel source that can quickly escalate a ground fire.
The structure of many cedars, especially the low-branching habits of species like Eastern Red Cedar, causes them to act as “ladder fuels.” They provide a direct path for fire to climb from the ground level into the canopy or directly to the roofline of an adjacent structure. Dry, dead foliage accumulates on lower branches and within the crown, contributing to the rapid spread of flames and showering embers downwind, increasing the risk of spot fires.
Beyond fire danger, the root systems of certain cedars, particularly Juniperus species, can threaten underground infrastructure. While roots rarely break intact foundations, they are aggressive moisture-seekers and exploit existing cracks in sewer lines, water pipes, and septic systems. Once inside, fine root hairs proliferate and form dense masses that block the flow, leading to costly plumbing failures and backups. Roots can also contribute to foundation damage indirectly by depleting soil moisture beneath shallow foundations during dry periods, causing the soil to shrink and leading to structural subsidence.