English Box - HELP

 Hi there all
I planted English Box in my garden as a hedge approximately two years ago.
(juvenile plants).
All had been fine until the end of last Summer. I noticed a few of the
plants going a copperish colour. I thought these plants were heat stressed
and did not worry. Through the Autumn and Winter allot more have gone this
colour.The plants discoloured seem to be not dried up. A nursery suggested I
get some lime and add to the mulch around the plants. This has not helped. I
treated the plants 7 weeks ago. Not all the plants have gone this colour and
some seem quite healthy. Does anyone have any suggestions as to what to do
next. Or is this normal for this type of plant to do over the Winter months.
Thanks Gareth

  

That is just the winter colour.  They will go green when it warms up.