Arborvitae (Thuja) are popular evergreen trees and shrubs often used for privacy screens, hedges, and landscape accents. These conifers are valued for their dense, scale-like foliage and low maintenance requirements, making them a common choice for year-round color. A frequently asked question is whether these plants can maintain their characteristic density when planted away from direct sunlight. The success of an arborvitae is highly dependent on receiving the correct amount of solar energy.
Arborvitae Light Requirements
Arborvitae thrive best in conditions ranging from full sun to partial shade, typically requiring a minimum of six hours of direct sunlight daily to maintain their ideal form. Partial shade means the plant receives sun for less than six hours, often in the morning or late afternoon. While arborvitae can survive in this less-than-optimal light, their growth habit will change compared to sun-grown specimens.
It is important to distinguish between partial shade and deep shade, as the latter is incompatible with a healthy arborvitae. Deep shade, such as under a dense tree canopy or on the north side of a building, offers insufficient light for the plant’s metabolic needs. Arborvitae planted in these dark areas will not flourish and will exhibit a noticeable decline in vigor. Even shade-tolerant cultivars struggle to produce the lush, full foliage for which the genus is known.
How Shade Affects Growth and Health
When arborvitae are situated in locations with inadequate light, their growth patterns change dramatically, failing to provide the intended aesthetic or screening effect. The most visible symptom of light deprivation is the thinning of the foliage, particularly on the interior of the plant. This causes the tree to become “leggy” or loose, compromising the dense, uniform shape sought after in a privacy hedge.
A lack of sunlight directly impacts the rate of photosynthesis, which stunts the overall growth of the plant. Arborvitae that might grow a foot or more per year in full sun may only add a few inches in a heavily shaded spot. Cultivars prized for their specific color, such as golden or variegated types, will often lose their vibrant hues and revert to a duller green in an attempt to maximize chlorophyll production.
Insufficient light can also indirectly increase the risk of disease by creating a constantly damp environment. Root rot, often caused by Phytophthora fungi, is exacerbated by poorly draining soil and the lack of sun to dry the foliage and topsoil. Reduced vigor from shade makes the plant more susceptible to various insect and fungal attacks. A weakened tree is less able to defend itself against common problems like twig blight and bagworms.
Selecting Appropriate Arborvitae Cultivars
For areas receiving less than the ideal six hours of sun, selecting a shade-tolerant species or cultivar is necessary. While common varieties like ‘Emerald Green’ (Thuja occidentalis) are best reserved for sunny spots, the Western Red Cedar (Thuja plicata) is generally recognized as being more forgiving of lower light conditions than its Eastern counterpart.
Specific cultivars of Thuja occidentalis have been developed that show better performance in partial shade. Varieties like ‘Holmstrup’ and ‘Techny’ are known for retaining their dense habit better when light is reduced. Certain compact or dwarf forms, such as ‘Tater Tot’, are also suitable for planting in locations with dappled shade. These selections provide a viable option for gardeners who need an evergreen screen but cannot offer a full-sun location.