Bryant RedHawk wrote:I would suspect the construction work was the cause of the hedge demise, that much root damage is not recoverable from by conifers or deciduous trees.
Each branch of a tree has a corresponding section of roots, main branches have main root sections, kill the root, kill the branch.
You state that this work was within one foot of the trunks, that is far to close for survival of the hedge plants, feeder roots are usually at least 3 feet distant from a trunk, within a foot, main roots were most likely cut thus killing the branches they were connected to.
Since the construction work has been done as well as the resulting damage, about the only thing to do is replant.
I would also try to do some soil improvement with addition of compost or compost extracts, this will improve the biology of the soil.
You will want to add fungi and bacteria with fungi being the higher number of organisms about a 2:1 ratio would be best, but what you add can only improve what is there now.