Reviving a struggling arborvitae starts with figuring out exactly why it is declining, because the fix depends entirely on the cause. Brown foliage, thinning branches, and stunted growth can stem from drought stress, root damage, pest infestations, fungal disease, or simply being planted too deep. Some of these problems are reversible with straightforward adjustments; others have already pushed the tree past the point of recovery. The key is reading the symptoms correctly and acting before the damage becomes permanent.
Read the Browning Pattern Before You Do Anything Else
Not all brown arborvitae foliage means the same thing, and treating the wrong cause can make the situation worse. The color, location, and timing of the browning are your best diagnostic tools.
Interior browning that appears in fall is usually natural shedding. Arborvitae are evergreen, but they still drop their oldest interior foliage once a year, typically in autumn. This looks alarming when it happens all at once, but if the outer foliage remains green and healthy, the tree is fine. No intervention is needed.
Browning that starts at the tips of branches and spreads inward usually points to drought stress, root damage, or a pest problem. Browning that appears in irregular patches scattered across the canopy often signals a fungal infection. Entire sides of the tree turning brown after winter usually indicate cold desiccation or salt spray damage. And if the foliage has gone uniformly brown from top to bottom in a short period, the root system may have failed entirely.
Before you reach for fertilizer, pruning shears, or a fungicide, spend a few minutes looking closely at the foliage. Scratch the bark on a brown branch with your fingernail. If you see green underneath, that branch is still alive and can push new growth. If the tissue beneath the bark is brown and dry all the way through, that branch is dead and will not come back regardless of what you do.
Water Stress Is the Most Common Culprit
Arborvitae have shallow, fibrous root systems that are surprisingly sensitive to both too much and too little water. Drought stress is the single most frequent cause of decline in landscape arborvitae, especially during the first few years after planting, but overwatering kills them too.
A drought-stressed arborvitae will show foliage that fades from bright green to a dull yellow-green, then progresses to bronze and finally brown. The tips of the branches tend to be affected first. If you push a screwdriver or finger into the soil around the root zone and it is dry at a depth of two to three inches, the tree needs water.
The fix is deep, infrequent watering rather than frequent light sprinkles. Aim to soak the root zone thoroughly once a week during dry periods, applying enough water to penetrate eight to twelve inches into the soil. A soaker hose or drip irrigation system left running for thirty to sixty minutes works better than a sprinkler, which wastes water on foliage rather than delivering it to roots. A two- to three-inch layer of mulch around the base helps retain moisture, but keep the mulch a few inches away from the trunk itself to prevent bark rot.
Overwatering creates the opposite problem. Arborvitae planted in poorly drained soil or in spots where water pools after rain develop root rot. The roots suffocate, and the foliage browns from the bottom up. If the soil around your tree is consistently soggy, improving drainage is more important than adding more water. In severe cases, you may need to transplant the tree to a better-drained location, though transplanting a large arborvitae is risky.
Planting Depth and Root Problems
A surprising number of arborvitae decline because they were planted too deep in the first place. When the root flare, the point where the trunk widens into the root system, is buried under soil or mulch, the trunk tissue stays constantly damp. This invites infection and gradually weakens the tree. A review of urban tree planting practices found that excess soil covering the rootball by more than about four inches can lead to infection, weakening, or death, and that the condition of the root system at planting time, including problems like circling or girdling roots, is one of the most serious factors affecting long-term tree survival.1Plants. Pre-Planting and Planting Factors and Practices Affecting Urban Tree Growth: With a Special Focus on the Root System and Its Condition—A Review
If your arborvitae is struggling and you cannot see the root flare at the base of the trunk, carefully pull back soil and mulch until you expose it. The flare should sit at or just above the surrounding soil grade. You may discover that the tree was planted several inches too deep, or that mulch has been piled into a “volcano” around the trunk over the years. Correcting this alone can sometimes reverse a slow decline.
Girdling roots, roots that wrap around the base of the trunk instead of growing outward, are another common hidden cause. They slowly strangle the trunk as both grow in diameter, restricting the flow of water and nutrients. If you find a thick root circling the trunk just below the soil surface, you can carefully cut it with a sharp saw or chisel. This is stressful for the tree but less harmful than leaving it to slowly choke itself.
Spider Mites and Bagworms
Two pests cause the most damage to arborvitae in the landscape: spider mites and bagworms.
Spruce spider mites are tiny, hard to see with the naked eye, and do their worst damage in cool weather, spring and fall rather than midsummer. They feed by puncturing individual leaf cells and sucking out the contents, which produces a fine stippling that eventually turns foliage bronze or brown. By the time the browning is obvious, the mite population may have already crashed on its own, making the damage look mysterious. Research on arborvitae mite infestations has involved detailed sampling of branch tips to assess populations, reflecting how difficult these pests are to detect without close inspection.2Oxford Academic. American Arborvitae, Spruce Spider Mite Control, Richland Co., Ohio, 1979 To check for mites, hold a white sheet of paper under a branch and tap the foliage sharply. Tiny moving specks on the paper confirm their presence. Horticultural oil or insecticidal soap sprays applied to thoroughly cover the foliage are effective, but timing matters: treat in early spring or fall when the mites are active, not in the heat of summer when they are dormant and beneficial predatory mites are doing the work for you.
Bagworms build distinctive spindle-shaped bags from silk and bits of foliage that hang from branches like small ornaments. Each bag contains a larva that feeds voraciously on arborvitae foliage through summer. A heavy infestation can strip a tree bare, and because arborvitae do not regenerate foliage on completely defoliated branches, bagworm damage can be permanent. Research on bagworm control has tested insecticide applications on heavily infested arborvitae, finding that treatment timing, ideally when larvae are still small in late spring to early summer, is critical for effectiveness.3Oxford Academic. Bagworm Control on Arborvitae, 1981 If the population is small, you can handpick the bags in winter or early spring before the larvae emerge and destroy them. For larger infestations, a Bacillus thuringiensis (Bt) spray applied when larvae are young is effective and low-toxicity. Waiting until the bags are large and well-sealed makes treatment far less successful.
Fungal Diseases That Brown Arborvitae
Several fungal pathogens target arborvitae foliage and twigs, though most are opportunistic, hitting trees already weakened by stress rather than taking down healthy ones.
Tip blight, caused by various Phomopsis and Kabatina species, kills the newest growth at branch tips, which turns brown and dies back a few inches. It tends to strike in wet spring weather. The dead tips are unsightly but rarely fatal on their own. Pruning out affected growth during dry weather and improving air circulation by thinning overcrowded plantings usually controls the problem. Fungicide sprays can help in severe or recurring cases but need to be applied preventively, before symptoms appear, which makes timing tricky.
Leaf blight caused by Didymascella thujina (historically called Keithia disease) is more of a concern for western red cedar but can affect other Thuja species. It produces small, dark fruiting bodies on dead leaf scales and can cause significant foliage loss in wet climates. Keeping foliage dry by watering at ground level rather than with overhead sprinklers reduces the risk.
Root rot from Phytophthora or Armillaria fungi is harder to treat because it attacks below ground. Symptoms mimic drought stress: foliage yellows and browns, growth slows, and the tree gradually declines. But the soil around the roots is often wet rather than dry. If you pull back mulch and find white fungal mats or a mushroomy smell at the base of the trunk, root rot is likely. There is no reliable cure for advanced root rot in arborvitae. Improving drainage, avoiding overwatering, and removing heavily infected plants to protect nearby trees are the practical options.
Winter Damage and How to Prevent It
Arborvitae are cold-hardy trees, but winter can still do serious damage, especially to exposed specimens. Research on Thuja occidentalis seedlings found that the lethal temperature for about half of tested specimens was around minus 23 degrees Celsius (roughly minus 9 Fahrenheit), indicating meaningful cold tolerance but also a threshold beyond which tissue dies.4PubMed Central. Freezing tolerance and recovery of arbuscular-mycorrhizal and non-mycorrhizal Thuja occidentalis But outright freezing is not the only winter threat. Desiccation, where foliage loses moisture to cold dry wind faster than frozen roots can replace it, is more common in landscapes. The foliage turns brown, typically on the side facing prevailing winds, and the damage shows up in late winter or early spring.
Preventing winter desiccation is easier than treating it after the fact. Water your arborvitae deeply in late fall before the ground freezes, so the root zone goes into winter well-hydrated. For exposed trees, burlap windscreens (not wraps that smother the tree, but freestanding barriers) on the windward side reduce moisture loss. Anti-desiccant sprays, waxy coatings applied to foliage in late fall, offer some protection but need reapplication and are not foolproof.
Heavy snow and ice can also splay arborvitae branches apart, especially on columnar varieties. Gently tying the branches loosely together with soft twine before winter helps them shed snow loads without splitting. If branches have already been bent out of shape, tying them back into position in spring usually works if the wood has not cracked.
Fertilizer and Soil Nutrition
Reach for fertilizer last, not first. Many homeowners assume a struggling tree needs feeding, but arborvitae are not heavy feeders, and applying fertilizer to a tree whose roots are damaged, waterlogged, or diseased can actually speed its decline by pushing growth the root system cannot support.
If you have addressed watering, drainage, and pest issues and the tree is still producing weak, pale growth, a soil test is worth the small investment. It tells you exactly what the soil is lacking rather than forcing you to guess. Arborvitae prefer slightly acidic to neutral soil, roughly in the pH range of 6.0 to 7.0. If your soil is strongly alkaline, which is common in areas with limestone bedrock or where concrete and morite leach into the ground, the tree may struggle to take up iron and other micronutrients even if they are present in the soil.
The same cold-tolerance study on Thuja occidentalis found that seedlings colonized by mycorrhizal fungi had higher foliar nitrogen and phosphorus concentrations during recovery from stress compared to non-mycorrhizal seedlings, particularly in those that had been exposed to cold but not lethally damaged.4PubMed Central. Freezing tolerance and recovery of arbuscular-mycorrhizal and non-mycorrhizal Thuja occidentalis This suggests that a healthy soil food web, not just raw fertilizer, plays a role in how well arborvitae bounce back from stress. Maintaining organic mulch around the root zone, avoiding excessive soil compaction, and minimizing the use of broad-spectrum fungicides that can harm beneficial soil fungi are practical ways to support mycorrhizal activity.
When fertilizer is warranted, a slow-release granular product formulated for evergreens, applied in early spring, is the standard approach. Avoid heavy applications of quick-release nitrogen, which pushes soft, succulent growth that is more vulnerable to cold, pests, and disease.
How Much Dead Growth Can an Arborvitae Come Back From
This is the question that determines whether reviving the tree is realistic. Arborvitae have a significant limitation compared to many other landscape trees and shrubs: they do not regenerate foliage from bare wood. If a branch loses all its green growth, that branch will not push new leaves. This means that large bare patches in the canopy are permanent, even if the rest of the tree recovers its health.
As a rough guide, if the tree still has green foliage on more than half its canopy and the trunk shows green tissue beneath the bark, recovery is plausible with proper care. The tree will not fill in bare sections, but healthy growth around those sections can gradually mask the damage, especially with light corrective pruning to shape what remains.
If more than two-thirds of the canopy is brown and dead, the tree is unlikely to recover in any aesthetically meaningful way. You may keep it alive, but it will look like a skeleton with tufts of green for years. At that point, removal and replacement is usually the more practical choice. Younger, smaller arborvitae recover more readily than old, large ones, partly because the root-to-canopy ratio is easier to rebalance.
Pruning a Damaged Arborvitae Without Making Things Worse
Pruning out dead wood is always safe and worth doing: it improves airflow through the canopy and removes tissue that can harbor fungal spores. Use sharp, clean shears and cut back to the nearest point where live green growth exists on the branch. Do not cut into bare brown wood hoping the branch will resprout. It won’t.
For shaping and thinning, late spring through early summer is the best time, when the tree is actively growing and can seal pruning wounds quickly. Avoid heavy pruning in late summer or fall, which can stimulate new growth that will not harden off before winter.
If the tree has been heavily damaged on one side, by wind, salt spray, or a pest infestation, you can selectively thin the healthy side to create a more balanced look while the damaged side is either masked by neighboring plants or slowly grows lateral branches to partially fill in. This is cosmetic management rather than a biological cure, but it can buy years of acceptable appearance for a tree that is technically healthy but lopsided.
When Arborvitae Are Planted Too Close Together
Arborvitae hedges are frequently planted with spacing that looks ideal at purchase time but creates serious problems within a few years. As the trees grow and their canopies merge, the interior foliage is shaded out and dies. This is normal biology: cells that get no light stop producing chlorophyll and are shed. But it means that if any tree in the row dies or is removed, the trees on either side have bare, brown flanks that will never green up again.
Overcrowding also restricts airflow, which encourages fungal disease, and forces root systems into competition for water. If your hedge arborvitae are declining, the problem may not be any single stressor but chronic overcrowding that has weakened all of them. Thinning by removing every other tree, painful as it looks initially, can sometimes rescue the survivors by giving them room to breathe. The remaining trees typically widen to partially fill the gaps within a couple of growing seasons, though never completely.
For new plantings, spacing arborvitae at least three to four feet apart for a hedge and six feet or more for specimen plantings prevents these issues. The hedge takes longer to fill in, but the individual trees stay healthier for decades.