Arborvitae (Thuja species) are popular landscape choices, valued for their dense evergreen foliage often used for privacy hedges. The sight of this typically vibrant green shrub turning brown is a common concern for homeowners. Since the plant cannot recover its green color once the foliage has browned, early diagnosis is important to save the remaining healthy portion of the plant. Understanding the difference between normal seasonal changes and signs of irreversible decline is the first step in assessing your arborvitae’s health.
Visual Indicators of Trouble
The first indication of a problem is a change in the color and texture of the foliage, which manifests in distinct patterns pointing toward different underlying issues. Browning that begins at the tips of the branches and progresses inward is commonly associated with winter burn or drought stress. This occurs when the foliage loses water faster than the root system can replenish it, often because the ground is frozen or the soil is too dry.
A patchy or scattered appearance of browning, where isolated sections turn color while others remain green, indicates localized damage. This might be caused by a pet repeatedly using the area or mechanical injury to a specific root or branch. When browning occurs only on one side of the shrub, especially the side facing south or west, it often suggests sun scald or winter desiccation from harsh sunlight.
Browning that starts at the base and moves upward can signal overwatering and root rot, particularly if the soil remains soggy. Conversely, an overall graying or yellowing across the entire plant, eventually turning brown, is often a symptom of severe underwatering or nutrient deficiency. Signs of insect activity, such as fine webbing from spider mites or bagworm cocoons, suggest pest-related decline progressing outward from the infestation area.
Distinguishing Natural Shedding from Serious Problems
Evergreen trees like arborvitae undergo a natural process of shedding older, interior needles, commonly called “flagging” or “fall browning.” This typically occurs in autumn. The dense outer growth blocks sunlight from reaching the inner branches, causing the oldest needles nearest the trunk to turn brown before dropping.
This natural shedding should not cause alarm, as it is confined to the interior foliage while the tips and outer layer of the branches remain green. If the browning occurs on the outer tips, affects the entire branch, or happens outside of the typical fall season, it signals stress or disease.
Browning that affects whole branches or sections points to a genuine problem, such as root damage, fungal disease, or severe environmental stress. Identifying where the browning originates—interior versus exterior—is key to differentiating between a normal physiological event and decline caused by factors like drought or pest infestation.
Simple Diagnostic Tests to Confirm Death
Once visual inspection suggests a problem, performing a simple scratch test confirms whether the tissue underneath the bark is still alive. This test focuses on the cambium layer, the thin band of living cells just beneath the outer bark responsible for transporting water and nutrients. Use a clean fingernail or small knife to lightly scrape away a tiny section of the outermost bark on a suspected dead branch.
If the exposed tissue is bright green and moist, the branch is still alive and may recover. A dull green or yellowish color suggests the tissue is alive but stressed. If the cambium layer is brown, dry, or brittle, that section of the branch is dead and will not produce new growth.
Repeat the scratch test, moving progressively closer to the main trunk until you find green tissue, indicating the living part of the plant. Another diagnostic is testing the flexibility of the affected branches. A healthy branch bends slightly, while a dead branch will be dry and snap easily. If the scratch test reveals brown tissue down to the trunk on multiple major limbs, and browning exceeds 50% of the canopy, the arborvitae is likely beyond recovery.