If a C. leylandii hedge is brown it usually means that the relevant tree(s) is/are dead or at least the brown bits are. Many would say that's the best state for them.
Assuming you want to keep it, cut out the dead bits and encourage the rest to fill the gap by judicious and careful pruning (I suppose - but someone else will be an expert on it...)
Posts
If a C. leylandii hedge is brown it usually means that the relevant tree(s) is/are dead or at least the brown bits are. Many would say that's the best state for them.
Assuming you want to keep it, cut out the dead bits and encourage the rest to fill the gap by judicious and careful pruning (I suppose - but someone else will be an expert on it...)