Most hedges have to be clipped after planting, and cut twice annually; in spring and late summer. A formal hedge, however, needs to be clipped more regularly to preserve its shape.
Many deciduous plants, particularly those with a naturally bushy, low-branching habit should be cut back by one third on planting, as should the evergreens box and shrubby honeysuckle. The very vigorous and vertical growers, such as hawthorn and privet, may be cut back to 15 cm (6 in). The year after, these species should be trimmed lightly, and then cut back by one-third in their second winter season. Once the hedge has achieved the ideal dimensions, trim it back yearly to within 6 mm (1/2 in) of the old wood.
Leyland cypress and other vigorous conifers are employed extensively as hedges. In most cases, cut only their side-shoots in early years, leaving the leading shoots untouched. The most vigorous species may need trimming 2 or 3 times within the growing season. Once the leading (apical) shoots have attained the desired height, cut them level to create a flat-topped, wider-growing hedge.
The majority of flowering hedges blossom on last year's wood, and so can be cut back after flowering. Nevertheless, Japanese rose (Rosa rugosa) ought to be cut back hard in late winter or even early spring. Fruiting hedges, such as pyracantha and cotoneaster, can be lightly trimmed either before or after flowering.
Close-leaved evergreen hedges, that do not allow light and rainwater to penetrate easily, might be best cut to a batter; that is, slightly narrower at the top than bottom. Consequently light can reach the lower parts of the hedge, preventing browning and shedding of the leaves on lower limbs.
It is very tough to judge accurately by eye while you're trimming a hedge; it's only when you have finished that any blunders become obvious. Strings attached to 4 posts or canes, one at each corner of the hedge and set at the height required, will provide a cutting line and help to maintain a straight edge.
Most hedges are cut with shears or an electrical trimmer, though informal hedges and those with big evergreen leaves should, where practical, be pruned with secateurs to avoid unsightly damage to the leaves. You should always wear heavy-duty gloves and safety glasses while trimming evergreens.
Mains-powered hedge-trimmers must be used with care; they could be very dangerous if mishandled. Always use a 'residual current device' at the socket to cut back the danger of electrocution should you cut the cable. Try and use a hedgetrimmer with a blade stopping time of a maximum of half a second, and a two-handed switch, where the cutter will only work when both hands are on it. You can minimise the risk of a hand coming into contact with the blades by using blade extensions. Should you have a tall and broad hedge you may need 60 cm (24 in) blades; otherwise, 40 cm (15 in) blades will be quite sufficient.