The frequency of trimming will depend on the purpose and situation of the hedge, the hedge species and the climate in the locality. Trimming frequency will also vary with the cycle of hedge management, halting for a period of years before the hedge is laid.
Hedges adjoining drives and lanes may need trimming twice a year in order to allow safe passage of traffic. This would normally be a trim in July, to cut back the early summer growth, and another trim in late autumn to cut back the second flush of growth. This level of trimming is only needed on drives or lanes which have no verge, and for hedges on banks alongside lanes. This frequency of trimming eventually weakens the hedge, as new growth is being constantly removed. The field side of the hedge should only have an annual or biennial trim.
Hedges which need to be stockproof will normally need an annual trim in order to promote dense twiggy growth which stock cannot easily see through. To minimise disturbance to wildlife, and to allow the winter harvest of hips and haws to be used by wildlife, this trim is best done in late winter.
Many hedges do not need to be stockproof, and can be maintained as a hedge with a trim every two to three years. Most of the common hedgerow species flower and fruit more freely on two to three year old wood, which in turn benefits insects, birds, small mammals and other wildlife. growth should not normally be left for more than three years, or it becomes too thick to cut cleanly with a flail. Hedges on any one holding should be cut in rotation, so there is always some two to three year growth.
The frequency of trimming also depends on the dominant hedge species. Hawthorn and blackthorn respond well to frequent trimming by producing dense growth, although flowering and fruiting may be restricted. Other species such as holly, wayfaring tree, guelder rose, crab apple, field maple and spindle do not respond so well to frequent trimming, and are better trimmed at two to three yearly intervals. Less frequent trimming is a considerable saving in cost for the landowner.
Newly-planted hedges should be pruned or trimmed carefully for the first two to three years after planting, in order to promote dense, bushy growth, particularly at the base of the developing hedge. This pruning is best done by hand (p50).
Newly-laid hedges also need careful trimming for the first couple of years, which should basically prune growth back to the shape of the hedge when laid (p82). This promotes growth from the base and from side shoots within the hedge.
