Principles of Pruning Plants

Principles of Pruning

Pruning is a means of maintaining shape and vigour by removing weak, crossed, diseased or dead growth from shrubs and trees.

Large shrubs and climbers with straggly, untended or diseased branches look unattractive and often fail to produce a good show of flowers or fruits. Though regular pruning may not be essential for many popular shrubs, growth may be improved if light is let into the centre by cutting away old branches. Some shrubs will produce larger — though generally fewer — flowers if pruned each year. Dead or diseased branches should be cut away immediately to prevent the spread of infection.

Three tools are used in pruning:

  • secateurs for removing shoots and small stems;
  • long-handled loppers for large stems;
  • and a pruning saw for large branches.

A sharp knife may also be needed for trimming large wounds.

When shortening branches, cut just above an outward-facing bud or shoot. Cut diagonally, parallel with the angle of the bud or shoot. When removing entire branches, cut flush with the trunk or main branch. Then trim the raw area with a sharp knife and paint it with a proprietary wound-sealing compound. This will prevent disease spores entering the shrub through the wound.

Shrubs which have been hard pruned — especially when this is an annual operation — benefit from a 5cm (2in) thick mulch of garden compost or decayed manure after pruning, plus 55g (2oz/2 tbs) per sq m/yd of a general-purpose fertilizer such as Growmore.

Young shrubs, whether evergreen or deciduous, seldom require pruning except for the removal of crossing branches or damaged shoot tips. Frosted and dead shoots should be cut back to healthy wood in spring. Young conifers may occasionally fork, in which case the weaker of the two leading shoots should be cut out at the base in early or mid spring. Sometimes a young shrub produces a fast-growing main stem; cut this back to induce branching.

Dead or Straggly Wood

This method of pruning plants applies to most shrubs, and may involve only the removal of a small piece of damaged branch. It can be carried out at any time of year after a long, straggly branch has developed, or after a storm when a branch has been damaged, for instance. Or, you might prefer to carry out a routine examination of all shrubs in the garden every spring.

Remove any dead or damaged wood, cutting back to a healthy, outward-facing shoot or bud. Then remove shoots that are particularly weak, cutting right back to a main branch. If any branches have grown straggly and unsightly, prune them by half to a strong shoot or bud facing outwards.

Do not remove any well-formed, healthy wood, or you are likely to cut off many of the buds that would produce flowers later.

Popular shrubs which need such regular pruning include camellias, rock roses, daphnes, euonymus, hebes, shrubby cinquefoils (Potentilla) and viburnums.

Overgrown Plants

Some shrubs, particularly evergreens, should not be pruned at all until, after many years, they become overgrown or bare at the base. Then, in spring, cut all the main branches down to within a few inches of the ground with a pruning saw or bow saw.

Mulch with garden compost or rotted manure and apply 55g (2oz or two tablespoons) per sq m/yd of a general-purpose fertilizer, such as Growmore. The shrub will not flower once again until the following year.

Popular shrubs that may require this treatment include the cherry laurels (Prunus laurocerasus and P. lusitanica), daisy bushes (Olearia), pernettyas and pieris, and the deciduous mock oranges (Philadelphus).

Flowers on New Shoots

Some shrubs flower mainly on shoots that have grown in the current season. To restrict their size, or to encourage larger but fewer flowers, they can be pruned in spring, just as growth is beginning to show.

Cut all last year’s shoots back to two or three buds or shoots from their base. Unless you want to remove a branch altogether, do not cut back into the older wood, as this might prevent new shoots from developing.

After pruning, mulch with a 5cm (2in) layer of garden compost or well-rotted manure and apply 55g (2oz or two tablespoons) per sq m/yd of a general-purpose fertilizer, such as Growmore.

Shrubs that can be pruned by this method of pruning plants include Buddleia davidii, caryopteris, ceratostigmas, coluteas, Cytisus x ‘Porlock’, fuchsias, indigos (Indigofera), deciduous Californian lilacs (Ceanothus), lippias, passion flowers (Passiflora), potato vine (Solanum crispum), santolina, Spanish broom (Spartium), most spiraeas and Tamarix pentandra.

Flowers on Last Year’s Shoots

Some shrubs flower on shoots grown the previous year. These can be pruned each year immediately they finish flowering —whether in spring, summer or winter. The pruning is aimed at keeping the shrub in bounds, or promoting larger but fewer flowers.

Cut each shoot that has borne flowers back to two or three shoots or buds from its junction with the parent stem. The new shoots will produce flowers in the next season.

Buddleia alternifolia, ornamental brambles (Rubus), brooms (Cytisus except Cytisus X ‘Torlock’), deutzias, kerrias, Prunus glandulosa, Prunus triloba, Spiraea X arguta and weigelas can all be pruned by this method.

Removing Old Wood

Some shrubs, most notably the common Hydrangea macrophylla, benefit from having some of the oldest growth removed almost at ground level each year.

In spring, cut out all three-year old stems, which are rough-looking and have sub-laterals as well as lateral branches. Make the cut within 2.5-5cm (1-2in) of the ground. You can also cut away some of the two-year-old stems, which have lateral branches but no sub-laterals.

Other shrubs which benefit from this method of pruning plants when they have become overgrown include barberries (Berberis), beauty-bush (Kolkwitzia amabilis), clethras, cotoneasters, flowering currant (Ribes sanguineum), forsythias, genistas, shrubby cinquefoils (Potentilla), snowberries (Symphoricarpos), Himalayan honeysuckle (Leycesteria), abelias and weigelas.

Controlling climbers

Leave most woody climbers unpruned until they get too large, then prune them after they have flowered. Prune non-flowering climbers in spring or summer.

Self-clinging climbers, such as ivies (Hedera) or climbing hydrangea (Hydrangea petiolaris), can be trimmed as necessary on the wall. Climbers that use supports, such as honeysuckles (Lonicera japonica and Lonicera periclymenum) and clematis, should first be detached from the supports. Then remove all side growths, leaving just the main stems.

If the main stems look extremely old, cut them out and tie in their place some of the younger ones — either shoots growing from ground level or from low down on the old stems.

Other woody climbers requiring this method of pruning plants once established include actinidia vines, Clematis armandii, Clematis macropetala, Clematis montana, ornamental grape vine (Vitis), Russian vine (Polygonum baldschuanicum), trumpet creepers (Campsis) and Virginia creepers (Parthenocissus).

05. November 2010 by Dave Pinkney
Categories: Garden Management, Garden Tools, Plants & Trees, Pruning | Tags: | Comments Off on Principles of Pruning Plants


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