The Green Giant Arborvitae (GgA) is a hybrid often chosen for its rapid growth rate, making it ideal for dense privacy screens or specimen trees. This evergreen adds several feet of height annually, requiring a robust root system to anchor and sustain its growth. Understanding this subterranean network is paramount for successful cultivation, as the root structure dictates proper planting distance, water management, and long-term landscape health.
Anatomy and Growth Habits of the Root System
The Green Giant Arborvitae does not develop a deep, anchoring taproot common to many large trees. Instead, it relies on an extensive, dense, and fibrous root system that primarily spreads horizontally. This structure provides stability for the tall, columnar canopy and is highly efficient at capturing water and nutrients. Most fine, feeding roots remain concentrated in the top 12 to 24 inches of soil, reflecting the tree’s adaptation to surface-level resource acquisition.
The lateral spread of the root system is substantial, reflecting the tree’s aggressive growth rate. Roots generally extend outward at least to the canopy’s drip line. For a mature GgA, which can reach 12 to 20 feet in width, the root spread can easily reach 15 to 20 feet or more from the trunk. This expansive network of fine roots allows the GgA to thrive and grow rapidly.
The vigorous nature of these roots makes the GgA an aggressive competitor for soil resources. When planted close together for a hedge, their dense network quickly colonizes the planting bed. They often outcompete nearby lawn grass, shrubs, and flowers for moisture and nutrients. Homeowners must manage irrigation and fertilization accordingly due to this competition.
Addressing Concerns About Root Damage and Invasiveness
A primary concern is whether the GgA’s roots are structurally invasive or destructive to built objects. The fibrous root structure generally poses a low risk to modern, solid concrete foundations. Unlike species with thick, woody roots that expand deeply, the GgA’s shallow, fine roots are typically deflected by an intact foundation wall. They lack the mechanical force to crack or penetrate a sound structure.
The term “invasiveness” applies more accurately to the tree’s high competitive nature in the landscape than its ability to damage a house foundation. However, the roots can present a risk to hardscapes and utility lines that are already compromised or sit close to the surface. Over many years, the pressure from expanding, shallow roots can lift or crack sidewalks, driveways, patios, and retaining walls.
The risk to buried utility pipes is low unless a pipe has an existing fracture or leak. GgA roots are not known for actively seeking out water from small cracks in solid sewer or water lines. To mitigate the risk of hardscape damage, focus on providing a sufficient buffer zone between the tree’s trunk and any paved surface affected by the lateral spread of its shallow root mass.
Planting Guidelines Based on Root Structure
The tree’s structural needs mandate proper setbacks to ensure long-term health and prevent conflicts with structures. To avoid issues with foundations, homeowners should plant Green Giants a minimum of 10 to 15 feet away from a primary structure, such as a house or garage. For smaller hardscapes like sidewalks, patios, or low retaining walls, a distance of 5 to 8 feet is advisable to account for decades of root expansion.
When planting, the physical handling of the root ball is crucial for encouraging healthy, outward growth. The planting hole should be dug two to three times as wide as the root ball, but only as deep as the root ball itself. This ensures the shallow, structural roots are not buried too deeply, which can lead to suffocation or decline.
For container-grown trees, gently tease apart or cut any roots circling tightly around the perimeter of the root ball. This prevents the roots from continuing to grow in a circular pattern, which can ultimately girdle the tree. For privacy hedges, spacing the trunks 5 to 8 feet apart is recommended for a dense screen. Allowing 10 to 15 feet between specimens ensures each tree has ample space to fully develop its expansive root system and mature shape.