put up a string line at the top or if its square at each ridge and keep cutting it when it gets to the string . youll be amazed how quickly it fills the spot . if you generally trim the top as part of its upkeep it stands to reasen it will go the two extra feet .

I'm having trouble with your description of a 'fern' hedge - the largest fern with woody trunks is a tree fern, but I doubt you've a hedge of those. If you don't know what the plant making your hedge is called, can you post a photograph for ID please, its difficult to advise correctly without knowing the plant concerned.

I was wondering if you were in NZ as I have seen hedges made out of Dicksonia. It would be prohibitively expensive in the UK though as we do not have them growing madly in the coutnryside. I wonder if is it some sort of Woodwardia? A photo as Bamboo has said would help a lot.

Thank you all for your quick replies. I will post a picture soon and would value your comments again. Thanks for your time so far.

It's occurred to me that you might be describing any of several conifers, some of which might conceivably be described as vaguely ferny. If so, a close up of leaves and a pic taken from further away to show a whole plant or some of the hedge would be good.

Sounds much like a xCupressocyparis.