Arborvitae are popular evergreen trees and shrubs, widely used in landscaping for their dense foliage and privacy screens. Understanding their root systems is important for successful cultivation, proper placement, and long-term health. This knowledge aids in informed decisions regarding planting, care, and interactions with nearby structures.
Arborvitae Root System Overview
Arborvitae have a fibrous root system, characterized by a dense network of thin, branching roots that spread outwards rather than deeply downwards. Most roots stay within the top 12 to 18 inches of soil, though some can extend to about 24 inches. Certain anchor roots may penetrate deeper, reaching 3 to 6 feet or more in optimal conditions.
The lateral spread of arborvitae roots often extends horizontally as wide as the tree is tall, or even 1 to 1.5 times its height. For example, a 10-foot-tall arborvitae may have roots spreading 10 to 15 feet from the trunk. This wide-spreading, shallow network provides stability and efficiently absorbs water and nutrients from the upper soil layers.
Factors Affecting Root Growth
Several factors influence arborvitae root depth and spread. Soil composition plays a role; roots penetrate loose, well-drained soils like loam more easily than compacted clay. Loamy soil, a mix of sand, silt, and clay, offers balanced drainage, aeration, and nutrient retention, encouraging healthier root development. Conversely, sandy soils may cause roots to spread further for water and nutrients, while heavy clay restricts deep growth and can lead to waterlogging.
Water availability also affects root behavior. Scarce water encourages deeper root growth, seeking moisture, while consistent surface watering may encourage shallower roots. Climate, including temperature and rainfall, impacts overall root development. Improper planting depth, such as burying the root ball too deep, hinders root development and can cause root rot due to lack of oxygen. Different arborvitae species or cultivars, like ‘Green Giant’ versus ‘Emerald Green’, show variations in root characteristics, though their shallow, fibrous nature is consistent.
Practical Considerations for Root Depth
The shallow, fibrous nature of arborvitae roots has several implications for landscaping. While not considered invasive, their lateral spread requires careful placement. Arborvitae roots pose a low risk to solid foundations, sidewalks, or underground utilities compared to trees with more aggressive root systems, but planting them a reasonable distance from structures is still recommended.
Appropriate planting distance from other plants or structures is important to allow sufficient space for root spread and minimize resource competition. For example, ‘Emerald Green’ arborvitae are often spaced 3 to 4 feet apart for privacy hedges, while ‘Green Giant’ may need 6 to 8 feet. Their shallow root system makes them sensitive to poor drainage and waterlogged conditions, which can lead to root rot. This shallow rooting also means they are less drought-tolerant than deep-rooted trees, requiring supplemental watering during dry periods to maintain health.
Root Care and Maintenance
Maintaining a healthy arborvitae root system involves specific care. Consistent, deep watering is important, especially during establishment and dry spells, to encourage roots to grow deeper without waterlogging. Watering deeply but less frequently helps train roots to seek moisture further down.
Applying a 2 to 3-inch layer of organic mulch around the plant’s base is helpful. Mulch retains soil moisture, regulates temperature, and suppresses weeds that compete for water and nutrients, supporting the shallow root zone. Keep mulch a few inches away from the trunk to prevent rot.
Avoid disturbing the shallow root zone, including excessive digging or soil compaction around the plant’s base. When planting, dig a hole twice as wide as the root ball but only as deep, ensuring the top of the root ball is level with or slightly above the surrounding soil. Proper fertilization, with a balanced, slow-release formula in early spring, supports overall root health. Newly planted arborvitae do not require immediate fertilizer.