Brown on an arborvitae is alarming, but much of it is either a normal seasonal change or damage from winter weather, not a sign that the tree is dying. Insects, fungi, soggy roots, salt, and even the neighborhood dog can cause brown that looks similar. Where the brown appears on the tree and what time of year it shows up are usually the best clues to the cause.
Brown Inside the Tree in Fall Is Usually Normal
Evergreen conifers drop their oldest, innermost foliage in fall and keep several years of newer growth on the outside.1Washington State University Extension. Seasonal Foliage Discoloration and Loss in Pacific Northwest Evergreen Conifer Trees Arborvitae and their relatives have overlapping scales rather than separate needles, so whole branchlets change color at once instead of single needles.2Washington State University Extension. Seasonal Foliage Discoloration and Loss in Pacific Northwest Evergreen Conifer Trees This seasonal browning can look severe even on a healthy tree.
In October, part the branches and look toward the center near the trunk. You’ll typically see brown branchlets sitting behind a green outer shell. They come loose easily when you shake or brush the tree, and the outer foliage keeps its normal green color.
Some insects and diseases also attack the oldest foliage first.3Washington State University Extension. Seasonal Foliage Discoloration and Loss in Pacific Northwest Evergreen Conifer Trees These usually leave signs such as fine speckling or chewed foliage.4Washington State University Extension. Seasonal Foliage Discoloration and Loss in Pacific Northwest Evergreen Conifer Trees Clean brown branchlets deep inside the tree in fall, with green outer growth and no speckling, can be left alone. Inner browning stops looking normal when it spreads to the outer growth or shows up in spring or summer.
Winter Burn and Hot, Exposed Spots
When the ground is frozen, roots can’t take up water.5Penn State Extension. Preventing Winter Burn on Evergreen Landscape Plants Meanwhile winter sun, wind, and temperature swings keep drawing moisture out of the foliage.6Penn State Extension. Preventing Winter Burn on Evergreen Landscape Plants Arborvitae foliage often turns brownish in winter, especially on cultivars with colored foliage and on sites open to wind.7EDIS. Thuja occidentalis: White Cedar
In March and April the damage shows up as the snow melts, often on the south, west, or windward side. The brown foliage may look dry and crisp rather than spotted, while branches on the sheltered side usually stay green.
Reflected heat can single out one side. Emerald Green arborvitae can burn when planted against a west-facing wall or where afternoon heat reflects onto it.8Guzman’s Garden Centers. Arborvitae Trees for the Southwest: 4 Best Types A light south wall, a white garage, or open snow can reflect a double dose of heat onto a hedge.9Three Timbers Minnesota. Why Is My Arborvitae Turning Brown? A Minnesota Diagnostic Guide
To see whether a branch is still alive, scratch a twig with a fingernail; green, moist tissue underneath means it is. Wait until late spring for new growth before pruning, then trim out only the branches that stay brown and brittle after the new growth appears.
Watering deeply in fall, before the ground freezes, helps the plant enter winter with moisture to spare. A burlap screen on the windward or sunny side can cut drying from wind and sun, and a layer of mulch over the roots helps the soil hold moisture.
Spider Mites and Leafminers
Spider mites are tiny sucking pests related to spiders. They empty plant cells, which first turn white and then die and turn brown.10Home Yard & Garden Pest Newsletter. Spruce Spider Mite Infested foliage shows fine yellowish speckling and looks discolored and unhealthy.11Hortsense. Arborvitae: Spider mites As damage builds, foliage can look bronze, reddish, or yellow.12UC Statewide Integrated Pest Management Program. Arborvitae Brown Spots: Why They Happen and What to Do Heavy infestations turn foliage brown and can kill branches or whole trees.13Hortsense. Arborvitae: Spider mites14Home Yard & Garden Pest Newsletter. Spruce Spider Mite
To check for mites, hold a sheet of white paper under a branch and tap the branch sharply. Tiny moving specks on the paper are likely mites. A magnifier will show fine webbing and speckles on the foliage. Repeat on several branches, since mites cluster.
A strong spray of water knocks mites off and can be repeated. Insecticidal soap or horticultural oil, applied according to the label, can also control them.
The arborvitae leafminer is a different problem. Its larvae burrow into the leaf scales and eat the insides.15Find a Pest. Arborvitae Leafminer They mine from the tips of branchlets toward the base.16NC State Extension Publications. Arborvitae Leafminer Mined foliage turns yellow, then brown, with a bleached look.17Find a Pest. Arborvitae Leafminer Tips may die completely, and at times whole shrubs turn brown.18NC State Extension Publications. Arborvitae Leafminer
Hold a browned tip up to the light. Mined scales look hollow or see-through. Squeezing a mined tip may reveal a small larva or dark debris inside. On small plants, pruning out and disposing of mined tips removes the larvae.
Fungal Blights on Branch Tips
Kabatina blight shows on branch tips in early spring but affects last year’s growth.19Home, Yard & Garden Pest Newsletter. Shoot Blights on Juniper and Arborvitae It usually follows injury such as winter damage or drought stress.20Home, Yard & Garden Pest Newsletter. Shoot Blights on Juniper and Arborvitae It doesn’t spread to new growth, so if fresh growth is browning, Phomopsis blight is more likely.21Home, Yard & Garden Pest Newsletter. Shoot Blights on Juniper and Arborvitae
Fungi often move in on weakened plants. Pestalotiopsis attacks plants already weakened by drought, insect feeding, mechanical damage, or planting stress.22Gurney’s Seed & Nursery Co.. What’s wrong with my arborvitae? Cedar leaf blight infects the leaflets of both young and mature trees in this family, reducing growth and sometimes killing seedlings.23Canadian Journal of Plant Pathology. Western redcedar — natural history and pathosystems, with emphasis on cedar leaf blight It is most common in warm, moist, low-elevation coastal areas.24Agricultural and Forest Meteorology. Predicting the risk of cedar leaf blight (Didymascella thujina) in British Columbia under future climate change
Wet foliage on cool nights encourages tip blight and leaf spot to spread,25Glover Nursery. The Beginner’s Guide to Arborvitae Fall Care so water at the base instead of overhead. Give hedges room so foliage dries faster after rain. For one tip blight, pruning out diseased foliage in early summer and spraying copper in early fall before the rainy season prevents new infections.26Agricultural Experiment Station, Oregon State College. Cause and Control of the Coryneum Blight of Oriental Arborvitae One fall spray was enough for healthy plants, while diseased plants needed a second.27Agricultural Experiment Station, Oregon State College. Cause and Control of the Coryneum Blight of Oriental Arborvitae
When you prune blighted tips, cut back into healthy green growth below the browned part. Choose dry weather so spores don’t spread on wet foliage, and clean your pruners with rubbing alcohol between cuts. Bag and remove the clippings rather than leaving them under the plant.
Browning From the Bottom Up Means Root Trouble
Many arborvitae with rotted roots grow on poorly drained, wet sites where roots run short of oxygen.28Pacific Northwest Pest Management Handbooks. Arborvitae-Root Rot Root rot fungi or water molds are sometimes involved.29Pacific Northwest Pest Management Handbooks. Arborvitae-Root Rot Above ground, foliage discolors overall and the tree eventually dies.30Pacific Northwest Pest Management Handbooks. Arborvitae-Root Rot
Phytophthora root rot comes from a soil-borne water mold that thrives in heavy clay, low spots, and anywhere drainage is poor.31Nature Hills Nursery. Why Are My Arborvitae Turning Brown? | Causes & Fixes Lower branches brown first and the browning moves upward.32Nature Hills Nursery. Why Are My Arborvitae Turning Brown? | Causes & Fixes The trunk base may feel soft or show dark, water-soaked patches.33Nature Hills Nursery. Why Are My Arborvitae Turning Brown? | Causes & Fixes Decline happens over weeks or months, not overnight.34Nature Hills Nursery. Why Are My Arborvitae Turning Brown? | Causes & Fixes
To check drainage, dig a hole about a foot deep, fill it with water, and see whether it drains within a day. Soil that stays soggy days after rain points to poor drainage. Also check whether downspouts or sprinklers soak the area.
Badly affected trees rarely recover and are best removed. Stop overwatering and redirect water away from the planting. If you replant, use a raised bed or a better-drained spot, not the same soggy hole.
Salt, Dog Urine, and Poor Soil
Salt spray kicked up by traffic dries out foliage and stems by pulling water out of the plant.35Arboriculture & Urban Forestry (AUF). Tree Stress from Salts and Herbicides Salt in the soil makes it harder for roots to take up water, especially in dry weather.36Arboriculture & Urban Forestry (AUF). Tree Stress from Salts and Herbicides Browning on the side facing a road or salted path suggests salt. Use plant-safe de-icers nearby and rinse the soil with deep watering in spring.
Dog urine can discolor foliage and kill branches.37Yardener. Arborvitae Brown Spots: Why They Happen and What to Do It can turn foliage dark, almost black, as if spray-painted.38Victory Garden Boys. Emerald Green Thuja Sensitivity: Chemical Burn Caused by Dog Urine A favorite marking spot gets repeated visits, so lower branches may be lost.39Victory Garden Boys. Emerald Green Thuja Sensitivity: Chemical Burn Caused by Dog Urine
Dog damage is low, usually below knee height, on the side facing a walkway. Low fencing or another barrier keeps dogs off the base, and rinsing the spot with water soon after dilutes the urine.
Nutrient problems are most common in very sandy soils, highly alkaline soils, and where trees compete with lawn grass.40Nature Hills Nursery. Common Arborvitae Problems and How to Fix Them An iron shortage yellows new growth, while a nitrogen shortage turns the whole tree pale.41Nature Hills Nursery. Common Arborvitae Problems and How to Fix Them For yellowing in alkaline soil, chelated iron or sulfur to lower the pH can help.42Nature Hills Nursery. Common Arborvitae Problems and How to Fix Them Get a soil test before adding fertilizer, and clear grass from around the base to reduce competition.
Girdling Roots, Broken Branches, and Planting Stress
Roots that wrap around and press on the trunk narrow the tissues that carry water and sap.43Arnoldia. Dysfunctional Root Systems and Brief Landscape Lives: Stem Girdling Roots and the Browning of Our Landscapes The tree can suffer water stress even in moist soil.44Arnoldia. Dysfunctional Root Systems and Brief Landscape Lives: Stem Girdling Roots and the Browning of Our Landscapes An early sign is scorching or wilting on one tree while nearby plants look fine.45Arnoldia. Dysfunctional Root Systems and Brief Landscape Lives: Stem Girdling Roots and the Browning of Our Landscapes This can progress to yellowing and early leaf loss, and stressed trees become more vulnerable to other problems.46Arnoldia. Dysfunctional Root Systems and Brief Landscape Lives: Stem Girdling Roots and the Browning of Our Landscapes
To check, gently pull back the mulch at the trunk base. A healthy trunk flares out at the soil line. Roots circling tight against the trunk are a warning sign, and an arborist can cut problem roots on established trees.
Heavy snow or ice can break branches.47Farm Progress. 5 causes of brown branches on arborvitae Follow a brown branch back to the trunk to look for a break or twist.48Farm Progress. 5 causes of brown branches on arborvitae Broken branches can be pruned whenever you find them.49Farm Progress. 5 causes of brown branches on arborvitae
On tall arborvitae, brush heavy snow off upward with a broom, and loosely tie multi-stem plants together for winter. Avoid shaking iced, frozen branches.
Will Brown Arborvitae Turn Green Again
Arborvitae rarely grow new foliage from old bare wood inside the plant. Cutting back past the green into bare branches can therefore leave a permanent hole. Trim only to just inside the brown and let surrounding branches fill in over a season or two.
If most of the tree is brown with no green tips by summer, it is unlikely to recover. A soft, dark trunk base points to root rot. Replacing one hedge plant is often easier than nursing it along.
A stressed tree that is still alive does better with deep watering during dry spells, especially in the first years. Keep mulch a few inches from the trunk, and avoid heavy fertilizing on a struggling plant.
Quick Guide to Reading the Brown
- Inside, near the trunk, in fall: normal shedding
- One side, after winter: winter burn or reflected heat
- Fine speckling or bronze cast: possibly spider mites (confirm with the paper tap test)
- Hollow, bleached tips: leafminers
- Bottom first, moving up: root rot
- Low, knee height, facing a walkway: dog urine
- Side facing a road: salt
- One tree only, others fine: girdling roots or a broken branch
If you still can’t tell, send a photo or sample to a local extension office plant clinic. Bring samples showing both healthy and browning foliage.