I planted 5 ft leggy copper beech for retaining hedge last March (late) and then cut back in mid/late july as the plants seemed to flourish. I have mypex down and bark mulch on top. Any risk the frost will kill them. Some neighbours suggested I should not have cut back in year 1
Beech is hardy and will be fine. The only danger to beech is heavy wet soil in winter which tends to kill the roots, so the drainage needs to be good.