The Emerald Green Arborvitae (Thuja occidentalis ‘Emerald Green’) is a highly popular choice for residential landscaping, favored for its narrow, columnar habit and dense, vibrant foliage. This cultivar is frequently used to create year-round privacy screens and formal hedges because it maintains a consistent, rich color through cold seasons. Achieving the plant’s signature deep color and tight, upright form depends significantly on its environment. The amount of light it receives is the most important determinant of its overall health and aesthetic appearance, dictating the density of the foliage and its ability to withstand stress.
Defining Ideal Sun Exposure
The Emerald Green Arborvitae performs best when situated in a location receiving at least six hours of direct sunlight each day (full sun). This intense light energy fuels the robust photosynthetic activity required to produce the thick, compact growth and deep green pigmentation for which the plant is valued. Direct sun is defined as uninterrupted light hitting the foliage, typically occurring midday and into the afternoon.
While full sun is ideal, this arborvitae can tolerate partial sun, meaning it receives between four and six hours of direct sunlight daily. A location receiving less than four hours of sun transitions into partial shade, which compromises the plant’s vigor and appearance. Moving toward the lower end of the light requirement spectrum will result in a noticeable reduction in the plant’s density and growth rate.
Mitigating Damage from Excessive Sun and Heat
Summer Scorch Prevention
Though the Emerald Green Arborvitae thrives in full sun, this high light exposure, particularly when combined with high temperatures in warmer climates, necessitates careful management to prevent stress. Summer sun can lead to foliage scorching, where the intense heat and light cause the outer needles to brown, often appearing first on the side facing the most direct afternoon sun. This damage is frequently linked to insufficient moisture, as more sun exposure increases the plant’s rate of transpiration, or water loss through its leaves. A consistent watering regimen is therefore directly proportional to the amount of sun the plant receives, with sun-exposed plants requiring more frequent, deep watering than those in partial shade. Applying a layer of organic mulch, approximately three inches deep, around the base of the plant helps retain soil moisture and also insulates the shallow root system, keeping the soil cooler in intense heat.
Protecting Against Winter Burn
Sun exposure also contributes to a phenomenon known as winter burn, which occurs when bright winter sun and strong winds cause the evergreen foliage to transpire and lose water while the ground is frozen. Since the frozen roots cannot replenish the lost moisture, the foliage desiccates and turns brown. To prevent this damage, a deep watering in late fall before the ground freezes is necessary to saturate the plant’s tissues with stored moisture. For plants in highly exposed locations, temporary windbreaks or burlap wraps can be erected on the south and west sides to shield the foliage from the combined stress of intense winter sun and drying wind.
Impact of Insufficient Light on Growth and Density
When the Emerald Green Arborvitae receives less than the minimum four to six hours of direct sun, its ability to maintain its characteristic compact shape and color is diminished. In shaded conditions, the plant allocates resources to vertical growth in an attempt to reach more light, resulting in a sparse or “leggy” appearance rather than the desired tight, columnar form. This lack of density is particularly noticeable on the shaded side of the plant, sometimes causing the lower sections to thin out entirely.
The signature emerald green color is also compromised when light is insufficient. Decreased light exposure reduces the production of chlorophyll, leading to a duller, yellowish-green or bronze hue instead of the rich, deep color the cultivar is known for. Reduced light levels also correspond to lower overall vigor, which makes the plant more susceptible to pests and fungal diseases.