Dying evergreen hedge

misc2013

We have a mature hedge, looks like eunonymus from photos but not sure about that. Basically it has been dying since the winter. It has now shed 50% of it's leaves. I presume it's because of the extremely wet cold winter, not enough sun etc. Is there any hope of it coming back? A quarter of it is healthier and I'm optimistic it will come back but the rest looks very poor. An odd shoot coming back here and there but a formerly thick healthy hedge is now transparent. It's bordering another garden so the privacy is gone too so I'm anxious about losing it altogether. All I can think of us to put some sand down to try and dry out the bed but maybe it's too late. Any magic superfood that won't just wash away?