Posted: 08/10/2013 at 14:06
Did you perhaps have any heavy machinery come in your garden this last year? Or has there been any digging done in the area where the hedge is growing? The rootsystem could have been compressed or damaged.
Also, are there any spots where the water doesn't drain away after heavy rain? Then there is a possibility that the layer of clay is too dense and forms kind of a "pool" down where the rootsystem is.
I agree with Clueless that you shouldn't feed a stressed plant; it causes them to grow while they need all of their reserves to save themselves. Just keep it well watered and give it a mulch ( do keep away from the stems) so the soil doesn't dry out.
Hope your hedge picks up again as these hedges are so valuable to wildlife and so beautiful.