Juniper is a common ornamental shrub prized for its year-round evergreen color and tolerance to various conditions. Many varieties are frequently planted close to homes as part of foundation landscaping. While junipers do not pose the same threat as large, aggressive trees, their roots can still cause structural issues by indirectly altering the soil conditions around a house’s concrete foundation.
The Nature of Juniper Root Systems
The juniper root system is characterized by a dense, fibrous mat of fine roots that spread widely but remain close to the soil surface. Unlike many large trees that develop a single, deep taproot, junipers focus their growth on lateral, shallow roots. These roots are highly efficient at absorbing moisture from the upper soil layer, allowing junipers to thrive in dry environments. The lateral spread of the root system is often much wider than the visible shrub above ground.
This expansive, shallow root structure is the primary factor influencing how the plant interacts with a nearby foundation. The roots are not woody or thick enough to exert the direct mechanical force seen with mature tree roots. Instead, their danger lies in their ability to draw large volumes of water from the surrounding soil, which becomes the mechanism for potential structural damage.
How Root Systems Interact With Foundations
The main way a juniper root system can compromise a foundation is through soil desiccation, which is especially problematic in certain soil types. Desiccation occurs when the roots draw significant amounts of water from the soil beneath and adjacent to the foundation footings. This constant water removal causes expansive clay soils to shrink dramatically in volume.
As the clay soil dries and shrinks, it pulls away from the concrete, creating a void and removing the necessary support the foundation relies upon. This loss of support leads to differential settlement, where one part of the foundation sinks unevenly. This uneven sinking causes cracks in the concrete, walls, and interior finishes. Since juniper roots are shallow and widespread, they can dry out large areas of surface soil, making them effective at inducing settlement damage in clay-heavy regions. The risk is pronounced for slab-on-grade foundations, which sit directly on the surface soil.
Direct mechanical pressure is less common with junipers. This issue is usually reserved for large, woody tree roots that expand in diameter over decades, pressing against and cracking concrete structures. Juniper’s fibrous roots lack the necessary girth and woody structure to exert this kind of force against a well-constructed foundation. While a root might exploit an existing crack, it is rarely the cause of the initial rupture. Therefore, the threat from a juniper is related to changes in soil moisture content.
Assessing Risk and Mitigation Strategies
Assessing the risk posed by a juniper involves considering the plant’s mature size, the soil type, and the planting distance from the structure. A general rule for planting shrubs near a foundation is to position them at least two-thirds the distance of their expected mature height or spread away from the wall. For example, a columnar juniper that reaches 15 feet tall should be planted a minimum of 10 feet away from the foundation.
For existing plantings that are too close, homeowners can employ several mitigation strategies to reduce potential damage. Maintaining consistent soil moisture around the foundation perimeter during dry spells is the most effective approach. Using a soaker hose or drip irrigation system ensures the soil remains stable and prevents the juniper roots from seeking water beneath the structure.
Installing a vertical root barrier is a permanent solution that can be used for established junipers. These barriers, often made of durable plastic, are placed in the ground between the plant and the structure to redirect root growth downward and away from the foundation. If the plant is severely crowding the foundation and causing visible structural movement, removal and replacement with a less thirsty, slower-growing alternative may be necessary.