We planted 45 local Lanark cedars on our property 5 years ago. They have grown beautifully into a cedar hedge 7 feet high. However 12 cedars in the middle of the row have recently turned greyish. We suspect a neighbour may be discharging grey water from his cottage property. We have watered heavily and applied bone meal to the water line of the cedars. Do you have any suggestions to remedy the damage or any suggestions as to the cause of this damage? The other cedars in the hedge are in excellent condition with no greying.
The Lanark cedar is the Eastern White Cedar (Thuja occidentalis), a native tree that does make a beautiful hedge. There are a number of possible explanations for the greying of some of the trees. The first is the December ice storm and the 2013/14 winter as a whole, which caused a lot of die-back in trees, especially evergreens. For a response to a very similar question, please see https://www.torontomastergardeners.ca/index.php/askagardener/tall-cedarswinter-damage/
However, the fact that your cedars are “greying,” not browning, may mean the presence of some other stress. It is unlikely that a neighbour’s grey water would be the cause. Trees will often die out in a group or in a particular section of a hedge due to problems in that section. This website may be useful in helping you identify the problem in your hedge:
Dying Cedar Hedges: What is the Cause? https://www.agf.gov.bc.ca/cropprot/cedar.htm