Hello,

I am sorry about your tree. Thank you for the picture, but it is difficult to identify the tree—it could be an arborvitae/white cedar (Thuja occidentalis) or a juniper/red cedar (Juniperus virginiana). The following information would in most cases apply to both species.

There are many factors that cause an arborvitae to brown, including improper planting, lack of water, too much water, improper drainage, insects, diseases and winter burn. Improper planting may lead to root issues whether it is too deep or shallow. How often do they receive water? Water is essential for the establishment of the tree especially after transplanting and right through the growing season. Evergreens need to receive at least one inch of water per week in well-drained soil up until the soil freezes. The soil should be moist but not wet since overwatering can also be detrimental and will show the same symptoms as too little water. Transplant shock may occur when the tree is grown in loose soil in the nursery and transplanted to soil that is clay and retains moisture. A soil test will help establish the condition of the soil. Go to: https://homesoiltest.msu.edu/get-started to obtain a soil kit. You can also establish the percolation rate of the soil. Read more here: https://www.canr.msu.edu/news/look_before_you_plant_landscape_trees

How you water may have an impact. If an above ground sprinkler hits the branches of the tree, they may break the branches and an attack by an opportunistic fungus such as Phomopsis twig blight. Read more about Arborvitae diseases here: https://extension.psu.edu/arborvitae-diseases

You have spread mulch below the tree which helps maintain moisture. Three inches is recommended and should be kept three inches from the trunk to avoid excess moisture against the bark which can cause rot and encourage insects.

Is the damage on the south side of the tree? If not protected, winter winds can be drying to the foliage that may result in browning. Read more here: https://hort.extension.wisc.edu/articles/winter-burn/

https://www.canr.msu.edu/news/tips_for_preparing_landscape_trees_and_shrubs_for_winter

Insects such as spider mites may cause damage to arborvitae. Check for mites by placing a white paper under a branch and give it a shake. The moving black dots that fall to the paper are mites. Read more here: https://extension.psu.edu/spruce-spider-mite

Attached is another article about stress related evergreen dieback: https://www.extension.purdue.edu/extmedia/id/id-477-w.pdf

Finally, for a definite diagnosis, you can submit a sample to MSU Extension’s Plant and Pest Diagnostic Lab: https://www.canr.msu.edu/pestid/ or you could contact a certified arborist.

To find an arborist in your area, go to www.treesaregood.org, the website of the International Society of Arboriculture.

I hope this helps you with your tree.

Thank you for contacting Ask Extension.