Redwing is right , do it randomly ; it will look much better in the future .
I have two mixed hedges about 200' long running up each side of my rather long garden ; there are a few exotics interspersed within ; but oak , beech , wych elm , dogwood , laurel , field-maple , cherry , ash , holly , hawthorn ,yew , blackthorn predominate . Four specimen silver-birch also for good measure !
Its been in about 25-years now , and I keep them about 5' wide and 6-7' tall . The best windbreaks ever for my centre borders .
I never weed the hedges as I believe they are valuable for insect/bird life ; nettles and ivy are abundant in them. All manner of native flora have appeared over the years . All I do is periodically keep them in check with my Stihl 'long-reach' trimmer .
Maybe or maybe not , I feel I'm trying to do my 'bit' for the local flora and fauna