What to Do if Thuja Occidentalis Trees Have Turned Brown

Narrow, dense, pyramidal conifers, Thuja occidentalis (American arborvitae) trees turn brown naturally in fall and in response to stress and infection. Growing 20 to 40 feet tall and 10 to 15 feet wide, American arborvitae trees are hardy in U.S. Department of Agriculture plant hardiness zones 2 through 7. Compact and dwarf cultivars are available, and American arborvitae tolerate annual pruning to restrict their size, making them useful hedging and screening plants. Thuja green giant arborvitae problems can usually be dealt with, making this an ideal plant even for those who don't have a lot of gardening experience.

Close Up of a Thuja Tree
credit: Lisa Schaetzle/Moment/GettyImages
What to Do if Thuja Occidentalis Trees Have Turned Brown

Arborvitae Shrubs Turning Brown

Thuja green giant arborvitae turning brown is part of the plant's normal growth cycle, along with the browning of many arborvitae varieties, and often trees require no treatment. Although American arborvitae are evergreen, the trees' inner branches turn brown and drop during fall and winter. Red-brown, mature bark sheds at the same time. American arborvitae outer foliage also turns yellow-brown, which may look unattractive but requires no treatment. Brush heavy snow buildup from branches to prevent breakage, and the trees' color will improve when new, fresh leaves appear in spring.

Harsh Conditions

Protection from cold winds and drought prevents American arborvitae shrubs from turning brown. Strong, winter winds cause brown, burned leaves in American arborvitae growing in exposed sites, and foliage also turns brown and die during prolonged drought, which these trees don't tolerate. Prune away the damaged foliage from winter conditions. If the entire branch is brown, scratch the bark on the affected branch and look for green underneath. Water your arborvitae well in a drought. If the foliage turns brown from drought, it may be too late to save it, so it's best just to prune away the dead foliage. Plant American arborvitae in sheltered, full-sun sites in moist, well-drained soil. Trees benefit from light afternoon shade in areas with hot summers and grow best in neutral or slightly alkaline soil. Water trees regularly so the soil remains moist but not sodden. Completely brown patches are probably dead and won't resprout, but new green growth may grow to cover them over time.

Leaf-Tip Blight

Leaf-tip blight turns American arborvitae leaf tips brown, and treatment involves pruning or spraying with fungicide. Symptoms of leaf-tip blight (Pestalotiopsis funerea) include tan or brown twig tips and small, black, pimple-like, spore-producing dots. Prune trees suffering from leaf-tip blight with pruning shears sterilized by wiping the blades with rubbing alcohol. Prune all affected areas, cutting 3 inches from the affected area into healthy, living tissue, and sterilize the pruning shears again after use. Alternatively, put on safety goggles and protective clothing, and spray foliage with a fungicide containing 58 percent copper salts of fatty and rosin acids, diluted at a rate of 1 tablespoon per gallon of water, or according to the manufacturer's instructions. Repeat applications every seven to 14 days or as required. Fungicides should be stored out of reach of children and wash hands after using.

Twig Blights

American arborvitae suffering from twig blights turn brown and require pruning. Kabatina twig blight (Kabatina thujae) infects 1-year-old American arborvitae branches, and phomopsis twig blight (Phomopsis juniperovora) can infect any branches. Infected tissue turns brown or ash gray as it dies, and dead branches remain on the tree for months. Small, black spots appear where dead tissue meets living wood. Prune American arborvitae suffering from twig blights with sterilized pruning shears, removing twigs and branches at least 3 inches inside healthy tissue. Bag and destroy all pruned branches. Fungicides to treat these twig blights aren't available for home use and can only be applied by professionals.


Jenny Green

Jenny Green

A graduate of Leeds University, Jenny Green completed Master of Arts in English literature in 1998 and has been writing about travel, gardening, science and pets since 2007. Green's work appears in Diva, Whole Life Times, Listverse, Earthtimes, Lamplight, Stupefying Stories and other websites and magazines.