Established hedges need regular trimming to keep them looking compact and dense. If you have formal hedges then these would need more frequent trimming.
New hedges need formative pruning within the first two years of planting which is usually carried out in winter or early spring.
Maintenance trimming is usually carried out once a year for informal hedges and twice yearly for formal hedges – generally between spring and summer. Any pruning to be done must take into account nesting birds which is considered March to August.