Beech hedges should be pruned, or trimmed, in August, according to the Royal Horticulture Society. Beech hedges should have longer shoots cut back the first two years of growth and the sides trimmed from the third year onward.
Beech hedges should have a flat-topped, A-shaped form with a little over three feet of width at the bottom and a taper upwards for best health. For larger branches, use a pruning saw to trim. They should not need wound treatment. After pruning, mulch and apply a general-purpose fertilizer. During the first growing season, water after pruning to keep hedges healthy, as well.