Our mixed native hedge on the western boundary, planted in early 2013, is maturing very nicely and is now a high, dense barrier.
There's only one problem - it's deciduous so we only have a full privacy screen from May to the end of October.
So we decided to supplement it with a parallel evergreen screen, by trimming the existing hedge back to half its thickness and then planting another hedge in front of it, i.e. on the eastern side. The plan is that eventually the existing hedge will be totally hidden by the new evergreen hedge.
Of course, the best time to have planted an evergreen hedge would have been four years ago, but we didn't and so the next best time is right now ...
We're a little unsure of how well a new hedge will grow in this position, but reckon that early summer is the best time to try - there's still a good five months of growing season ahead this year - and in any event if it fails to take then we've still got the deciduous hedge so we'll be no worse off than we are now.