Arborvitae are popular evergreen trees and shrubs, often chosen for privacy hedges and ornamental landscaping. Understanding their root system is important for successful planting and long-term care.
Arborvitae Root System Characteristics
Arborvitae generally possess a shallow, fibrous root system that spreads horizontally rather than deeply. This network of fine roots effectively absorbs surface water and nutrients in the upper soil layers. While predominantly shallow, the root structure can adapt to environmental conditions.
Arborvitae do not typically develop a large, single taproot like some other tree species. Their widespread, shallow network helps anchor the tree and supports its stability, especially in moist conditions.
Specific characteristics vary among different arborvitae varieties. For instance, ‘Green Giant’ arborvitae have a more extensive and deeper root system compared to ‘Emerald Green’ varieties. However, the general tendency for shallow, spreading roots remains consistent.
Root Depth and Spread
Most arborvitae roots typically reside within the top 12 to 18 inches of soil. While these shallow roots are the main zone for water and nutrient uptake, some deeper feeder roots can extend down to 3 to 6 feet or more under optimal conditions. The lateral spread often extends about 1 to 1.5 times the tree’s height.
Soil type significantly influences both depth and spread. In loose, well-drained soils, roots penetrate more easily and grow deeper. Conversely, in compacted clay or waterlogged areas, root growth may be restricted, leading to a shallower, wider spread.
Water availability also plays a role in root development. If water is consistently available near the surface, roots may remain shallower. In drier conditions, roots will grow further and deeper in search of moisture. Tree age and size also impact the root system, with mature specimens developing more extensive networks.
Potential Root Concerns
Arborvitae roots are generally not considered aggressive or destructive compared to other tree species. They are less likely to cause significant damage to foundations or sidewalks. Instead, roots typically exploit existing cracks or weaknesses in old or compromised foundations, pipes, or pavement as they grow.
Concerns about roots invading underground pipes are more relevant if pipes are already leaky or damaged, providing a readily available water source. Healthy, intact pipes are less likely to be penetrated. While their shallow root system might occasionally raise pavement or sidewalks if planted directly adjacent, this is often less severe than with trees known for more robust, surface-oriented root growth.
The fibrous nature of arborvitae roots makes them less capable of exerting the force needed to create new structural damage. This characteristic contributes to their reputation as a relatively safe choice for landscaping near structures.
Managing Arborvitae Roots
Proper planting distance is a key strategy for managing arborvitae roots and preventing future issues. For individual trees, plant them at least 5 to 10 feet away from house foundations, driveways, or other structures. For hedges, space ‘Emerald Green’ arborvitae 3 to 4 feet apart, while ‘Green Giant’ varieties may require 6 to 8 feet between plants for proper development.
Watering techniques directly influence root depth. Deep, infrequent watering encourages roots to grow deeper in search of moisture, promoting a more stable, resilient plant. This contrasts with frequent, shallow watering, which keeps roots near the surface and can make the plant more susceptible to drought and wind damage.
Applying a 2 to 3-inch layer of organic mulch around the base helps retain soil moisture, regulate soil temperature, and suppress competing weeds. Ensuring the planting hole is wide, at least twice the width of the root ball, allows roots ample space to spread and establish effectively.