Cedars are beautiful, aromatic conifers often celebrated for their stately presence in the landscape. Their large size and dense canopy are often the primary focus, but what lies beneath the soil dictates their long-term impact on a property. Understanding the root structure of a cedar tree is important for anyone planning to plant one near a home or existing infrastructure. This knowledge helps homeowners and gardeners make informed decisions to ensure the tree’s health and prevent costly damage to their surroundings.
Distinctive Characteristics of Cedar Root Systems
The term “cedar” is commonly applied to a wide array of trees, but their root structures vary significantly depending on whether they are true cedars or “false cedars.” True cedars belong to the genus Cedrus, which includes the Atlas, Cyprus, Deodar, and Lebanon cedars. They typically develop a strong taproot when young, though this system transitions to a more wide-spreading structure as the tree matures.
Most trees commonly referred to as cedar in North America, such as Eastern Red Cedar (Juniperus virginiana) and Arborvitae (Thuja species), are actually in the cypress family. These landscape varieties are characterized by a dense, fibrous, and shallow root system, often described as a root mat. This shallow structure is an adaptation to help the tree efficiently capture surface moisture and oxygen. This root mat provides the tree with stability, but it means the majority of the root mass is concentrated very close to the soil surface.
Typical Root Depth and Spread
The majority of a cedar tree’s absorbing roots are not found deep underground but instead thrive in the top 6 to 18 inches of soil. This surface concentration is due to the soil in this layer providing the best balance of water, nutrients, and oxygen needed for root growth. Even for very large trees, the deepest roots are typically only found a few feet down, with the most active feeder roots remaining close to the surface.
While the depth is limited, the lateral spread is extensive and is the primary characteristic to consider when planting. A cedar’s root system can easily spread out to two to three times the width of the tree’s canopy or its mature height. For a mature cedar that reaches 50 feet tall, its roots may extend 100 to 150 feet in every direction, forming a wide, subsurface network. This broad, shallow root plate supports the massive size of the tree, sometimes exhibiting buttress roots near the trunk, especially in wet or shallow soil conditions.
Potential for Infrastructure Damage
The wide, dense, and shallow growth habit of cedar roots creates specific risks for nearby structures and utilities. Tree roots are not strong enough to crush solid pipes or foundations; instead, they exploit existing weaknesses by seeking out sources of water and nutrients. Any small crack, loose joint, or corrosion in an underground sewer or water line will release moisture, which attracts the fine, hair-like roots of the cedar.
Once inside a pipe, the continuous availability of water and nutrients allows the roots to grow rapidly, expanding into a dense mass that creates blockages and pressure. The expansion of this root mass can cause the pipe to crack further or burst, leading to costly blockages and sewage backups. Above ground, the lateral growth of these roots can physically lift and crack hardscapes like sidewalks, driveways, and shallow foundations. This damage is a result of the roots expanding within the confined space beneath the pavement, gradually displacing the surrounding material.
Strategic Planting and Root Management
Mitigating the risk of root damage begins with strategic planting, which requires accurately estimating the tree’s mature size and root spread. For large cedar varieties, a planting distance of at least 30 to 50 feet from a house, septic system, or main sewer line is advised to avoid future conflicts. A good rule of thumb is to allow a distance equal to half the tree’s estimated mature height from any structure.
For existing trees causing problems, root management must be approached with caution, as severing major roots can weaken the tree’s stability and health. Root pruning should only be performed under the guidance of a certified arborist. Cuts should be made at least 5 to 8 feet away from the trunk to minimize stress. If a physical barrier is necessary, a heavy plastic root barrier can be installed vertically in a trench to redirect root growth away from a structure.