Answer: Although extremely hot or extrememly cold weather can cause Thuja foliage to turn brown, it's more likely that your shrub is suffering from a root problem. Too much or too little water can cause browning foliage in newly planted Thuja's. Check the root health by digging the ailing shrub up and inspecting the roots. Healthy roots will be a creamy white inside; rotted roots will be brown or rusty colored and there may be an odor associated with the root mass. If the roots look healthy, replant and water it in well, then carefully inspect the foliage for insect pests. If you still can't find any physical clues to explain its decline, take a sample of the affected foliage (sealed in a plastic bag) to your local nursery or Cooperative Extension office for diagnosis. Best wishes with your landscape!
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