Arborvitae, belonging to the genus Thuja, are evergreen trees and shrubs often used for creating dense, year-round screens and hedges. Their columnar or pyramidal growth habit makes them a popular choice for defining property lines or establishing privacy in residential settings. When planning to incorporate these plants into the landscape near a home, the question of planting distance requires careful consideration. Failing to account for the plant’s mature size can lead to significant issues with the shrub’s health and the maintenance of the adjacent structure.
Understanding Mature Size and Variety
The precise distance an Arborvitae should be planted from a house depends entirely on the specific cultivar chosen and its ultimate mature width. Homeowners must consult the plant’s tag for the mature spread, not the current size, as Arborvitae can take a decade or more to reach their full dimensions. Selecting a variety with a narrow profile is crucial for successful planting near a structure.
The ‘Emerald Green’ Arborvitae (Thuja occidentalis ‘Smaragd’) is a slender, compact cultivar that typically matures to a width of 3 to 4 feet, making it suitable for tight spaces. In contrast, the ‘Green Giant’ (Thuja standishii x plicata ‘Green Giant’) reaches a mature spread of 12 to 15 feet and towering heights, requiring a much greater setback. A medium option, the ‘Nigra’ (Thuja occidentalis ‘Nigra’), grows to 8 to 10 feet wide. Failing to account for the mature spread means the plant will eventually grow into the house, confirming that a single planting distance does not apply to all varieties.
Calculating the Minimum Safe Planting Distance
The most reliable rule of thumb for determining the minimum safe planting distance is to place the center of the Arborvitae’s trunk at least half of its mature width away from the structure. For plants with a mature width of 4 feet, this suggests a minimum distance of 2 feet from the house, measured from the foundation wall. However, adding an extra foot for a total of 3 feet is strongly recommended to account for long-term health and maintenance access.
This setback provides adequate air circulation around the foliage, which is a primary reason for maintaining distance. When dense evergreen foliage is pressed against a solid wall, it impedes air flow, creating a moist microclimate that encourages the development of fungal diseases like blight. This close proximity also prevents the inner foliage from receiving enough sunlight, causing it to brown and die off.
The distance is also necessary for home and plant maintenance. A minimum clearance is required to walk behind the shrub for pruning or applying treatments. Space is also needed for tasks such as painting the siding, repairing gutters, or performing routine foundation checks. A ‘Green Giant’ (12-foot width) requires a minimum 6-foot setback, though 8 feet is often recommended to ensure comfortable access and prevent branches from scuffing the siding.
Preferred Distance for Narrow Varieties
For the narrower ‘Emerald Green’ variety, a minimum planting distance of 3.5 to 4 feet from the trunk center to the foundation is preferred. This measurement ensures that the mature foliage does not constantly rub against the structure, which can damage the plant and the home’s exterior finish. Calculating this distance based on mature size prevents future overcrowding.
Addressing Foundation and Root Concerns
One of the most common fears concerning planting large shrubs close to a house is that the roots will damage the foundation. Arborvitae roots are generally shallow and fibrous, forming a dense, non-aggressive root ball that primarily occupies the top 10 inches of soil. Unlike trees with deep taproots or aggressive root systems, Arborvitae typically pose no threat to modern, structurally sound concrete foundations.
The primary root concern is interference with shallow underground utilities or drain tiles. The dense, fibrous root mass can proliferate and potentially clog or displace older, cracked pipes that lie close to the surface. It is prudent to avoid planting directly over known utility or drainage lines.
A more immediate concern of planting too close involves moisture retention against the house siding. When foliage is pressed against wood siding or stucco, it traps moisture, preventing the material from fully drying out. This constant dampness can lead to wood rot, paint failure, and create favorable conditions for pests like termites or carpenter ants. Maintaining a distance that allows for air circulation is the best defense against these issues.