How to Prune Hedges
While theof shrubs and fruit trees is a matter of choice – they will continue to ‘perform’ if let alone – it is a necessity with hedges, which must be tailored to shape. The term pruning is not often used by the gardener when he clips or trims the hedge, but that is what he is doing. The cuts are aimed at restricting or redirecting growth, and that is what pruning is all about.
The degree of growth control varies greatly, however. More often than not a formal feature is desired which is regularly trimmed into a neat oblong shape, an elongated pyramid or a loaf of bread outline. A well-managed hedge of this type is evenly textured from ground to top. The opposite is not uncommon – a bare base, a matted middle and a sparse, spindly top.
The informal hedge, as the name implies, can be treated with more lax discipline. It is enough that growth should be fairly even. Flowering shrubs are chosen for informal hedges and are permitted to extend their flowering shoots naturally.
A well-maintained hedge will cost less than a fence or wall in the long term and will filter wind, so avoiding the dangerous turbulence caused by solid barriers. The effort of training is amply rewarded by the natural beauty.
The approach to pruning is governed by the nature of the hedge. With small-leafed plants (which are chosen for formal hedges), overall trimming with shears or powered trimmer is the rule. With large-leafed subjects, such as laurel or rhododendron, prune with secateurs (pruning shears), because the effect of leaves severed by shears or clippers is unsightly and causes the leaf edges to discolour. There may be times when drastic measures are necessary in order to thin out and revive a hedge. At such times when old wood must be severed, a narrow-bladed saw is the best tool.
A basic rule relating to hedge shape is this: prune so that the bottom is wider than the top. This allows the whole surface area to get an equal share of light. All parts will then grow evenly and the base will not become bare.
Begin pruning as soon as a newly planted hedge is established and making growth. To get the desired well-clothed base, clip off at least half the length of the new shoots three or four times each year until the young hedge is evenly dense. After this it will need attention once, twice or perhaps three times a year. It is the ubiquitous privet that demands the most trims. If privet and thorn are to look their best, three trims are needed, starting in early summer with follow-ups at six-week intervals. The relatively slow-growing yew and Lonicera need several light trims if they are to keep a close ‘finish’.
Summer is the time to give the single annual clip that is enough for a great number ofplants – beech among them. The table which follows summarizes the best available hedging subjects, and the pruning treatment for each is given in the following section.
Tools for hedge trimming must be in good condition. Shears that are blunt or out of alignment will tear growth and give an unsatisfactory finish – to say nothing of leaving the gardener tired and frustrated from unrewarding effort. Likewise see that secateurs cut evenly. Both can be professionally sharpened during the winter. A power-driven trimmer must be maintained as befits any electrical appliance, and great care taken in its use – especially if it is cable-trailing rather than battery powered.
Cutting a hedge straight by eye is not easy. A good aid is a tight line stretched between posts of equal height to indicate the topmost level of cut. On relatively short lengths, two canes alone pushed into the ground to equal height will suffice. A hedge tapering to a narrow top is the easiest to trim, as well as being best for growth. Always hold shears and power trimmer flat against the surface: never poke the tip into the hedge. Be sure to cut back long shoots that ‘fill a gap’. Being cut they will branch and fill the gap better. Always shake the hedge to dislodge clippings, and clear them from the base.
HOW AND WHEN TO PRUNE HEDGES
Beech (Fagus) – trim to keep dense and regular in late summer or winter; brown leaves stay on through winter.
darwinii – lightly after flowering in spring; form berries later.
Berberis stenophylla – lightly after flowering in spring; flowers form berries later.
– lightly to restore shape, in winter (after autumn foliage effect).
Berberis thunbergii atropurpurea nana – does not exceed 60 cm (2 ft); trim in winter to maintain formal shape.
Berberis thunbergii erecta – lightly in winter; makes a narrow hedge.
Berberis verruculosa – lightly to restore shape after flowering in spring; flowers form berries later.
Box (Buxus) – lightly as required in spring and summer.
Chamaecyparis lawsoniana and forms – cut leading central shoot when desired height is reached. Trim in summer to limit spread.
Cotoneaster lacteus – lightly to restore shape in summer, with regard to winter berry effect.
Cotoneaster simonsii – trim this semi-evergreen lightly to shape in winter after berry and leaf effects have been enjoyed.
Cupressocyparis leylandii – treat as for Chamaecyparis above.
Cupressus macrocarpa – as above.
Escallonia – lightly in spring, and again after flowering in summer to encourage more flowers. Except near the sea, frost may cut back this shrub.
japonica – use pruning shears to avoid unsightly cut leaves; lightly to maintain shape in spring.
Griselinia – lightly in early summer; a tender shrub except near the sea.
Hebe (Veronica) – trim to shape in spring; can be cut back hard if getting leggy.
Holly () – lightly to restore shape in late summer, with regard for winter berries. Cut back regularly when young to keep bushy at base.
Hornbeam (Carpinus) – as for beech above.
Laurel (Primus laurocerasus) – use secateurs (pruning shears) to avoid unsightly cut leaves; cut to maintain shape and density in spring.
Lavender (Lavandula) – lightly in spring, and cut off dead heads after flowering.
Lonicera – frequently when young to achieve basal thickness; when mature, in spring and summer as required to maintain shape.
Myrobalan plum – frequently when young to achieve basal thickness; when mature trim twice in summer.
Olearia – lightly after flowering in summer.
Osmarea – lightly after flowering in summer.
Pittosporum – lightly to restore shape in spring or summer.
Privet – frequently when young to achieve basal thickness; later as required during summer; rejuvenate by hard cutting-back in mid-spring.
Prunus cistena – as below, but restrict new growth to 15 cm (6 in) after flowering.
Prunus pissardii – frequently when young to achieve basal thickness; when mature cut new growth well back to 45 cm (18 in) after flowering in spring.
Pyracantha rogersiana – lightly as flowers and fruit are carried on two-year-old wood; in spring after flowering.
Quickthorn () – frequently when young to achieve basal thickness; when mature trim to shape in summer.
Rhododendron ponticum – as little as possible with secateurs (pruning shears) to maintain outline; summer.
Rosemary – lightly to shape in spring.
Roses – hybrid teas and floribundas hard when young; moderately to maintain shape when mature. Shrubneed old wood cut out at base and long shoots shortened to maintain shape; main pruning early spring, shoot shortening in summer.
Santolina – lightly after flowering in spring.
– lightly in spring to maintain shape.
Snowberry (Syniphoricarpus) – lightly in spring with regard to winter berries.
Syringa () – as little as possible with secateurs (pruning shears) after flowering.
Thuya – as for Cupressus above.
Viburnum tinus – lightly in summer with secateurs (pruning shears).
Yew (Taxus) – trim to maintain shape in late summer; rejuvenate at base by hard cutting back.