Arborvitae (Thuja) are highly favored evergreen trees used for creating dense screens and privacy hedges. The success and effectiveness of a planted hedge rely on selecting the correct initial spacing between plants. This decision determines how quickly the hedge provides privacy, as well as the health and aesthetic outcome of the mature planting. Incorrect planning can lead to significant problems.
Identifying Your Planting Purpose
Defining the desired function of the hedge is the first step in determining planting density. A tight, formal privacy screen requires plants to be placed closer together to achieve immediate visual blockage upon maturity. This dense approach forces the trees to grow into a unified, solid wall of foliage.
Conversely, an informal boundary or loose screen allows for greater space between plants. Wider placement encourages each tree to develop its natural, conical shape, resulting in a less structured appearance. If the goal is to feature a specimen plant, the spacing must accommodate the full, unrestricted mature width of the tree.
Specific Spacing Requirements by Variety
The necessary distance between plants depends highly on the chosen variety, as mature widths vary drastically across the Thuja genus. For creating a dense, formal hedge, narrow columnar varieties are often preferred due to their compact growth habit. The popular ‘Emerald Green’ Arborvitae (Thuja occidentalis ‘Smaragd’) should be planted 2 to 3 feet apart, measured center-to-center.
This tighter spacing ensures the foliage quickly interlocks to form a solid visual barrier. Planting at the minimum 2-foot distance provides the fastest closure, while 3 feet offers slightly better long-term air circulation. These measurements are for a finished hedge height of around 12 to 15 feet.
For faster-growing, larger screening varieties like the ‘Green Giant’ (Thuja plicata x standishii), spacing must be significantly increased. These trees have a mature width that can exceed 12 feet, requiring more room to develop structurally sound branches. A dense, long-term screen using ‘Green Giant’ is achieved by planting them 5 to 6 feet apart, center-to-center.
If the goal is a less formal, quicker-growing screen that relies on height rather than immediate density, the distance can be stretched to 8 to 10 feet apart. Spacing closer than 5 feet can lead to significant overcrowding and eventual lower branch dieback as the trees mature. For a true standalone specimen, any Arborvitae variety should be planted at a distance equal to or greater than its full expected mature width, often 15 to 20 feet away from structures or other large plants.
Calculating Total Quantity Needed
Once the ideal spacing measurement is determined, calculating the total quantity of plants needed is a straightforward mathematical process. First, accurately measure the total linear distance of the area where the hedge will be planted in feet.
The calculation requires dividing the total length of the hedge line by the chosen spacing distance in feet. For example, a 100-foot hedge with a required 5-foot spacing would be 100 divided by 5, which equals 20 intervals.
It is important to add one extra plant to the result of the division to account for the starting point of the hedge. The formula is: (Total Linear Feet of Hedge / Required Spacing Distance in Feet) + 1 = Total Plants Needed. Using the center of the planting hole as the reference point ensures uniform placement and consistent growth.
The Impact of Incorrect Spacing
Adhering to the correct measurements is fundamental to the long-term health of the entire screen. Planting Arborvitae too closely together creates significant challenges by reducing air circulation around the dense foliage. Poor air flow traps moisture, significantly increasing the susceptibility to fungal diseases, such as needle blight.
Overcrowding also leads to intense competition beneath the soil line, where roots fight for a finite supply of water and nutrients. This competition often results in stunted overall growth and can prevent the trees from reaching their expected mature height. Furthermore, the lack of adequate side-light causes the lower branches to die back, leaving the base of the hedge thin and woody.
Alternatively, spacing the plants too far apart presents problems related to function. While wide spacing promotes individual health, it leaves significant gaps that can take many years to fill in completely. If the primary goal is immediate privacy, this extended waiting period renders the initial planting ineffective.