The answer to 'why is my hedge dead trees' is that there are several common causes for a hedge to die, including drought, disease, pests, and improper maintenance. The symptoms may include browning or wilting leaves, bare patches, and the entire hedge turning brown and dying off.
Some of the most common causes are lack of water, fungal diseases like root rot, insect infestations like aphids or mites, and improper pruning or shearing. To fix a dying hedge, you'll need to identify and address the root cause. This may involve watering regularly, treating for pests or diseases, and pruning properly. If the entire hedge is beyond saving, you may need to remove and replace it.