Pruning of Established Trees and Shrubs
As an annual operation and prior to any kind ofa number of basic tasks must be performed. Any dead, damaged and diseased wood, and suckers at their point of origin, must be removed from all trees and shrubs. Crossing branches and thin crowded shoots should be cut out, and thin weak shoots removed completely or cut hard back. Shoots which are showing reversion, a common complaint with the foliage of variegated plants and an occasional occurrence with flower colour, (e.g. in camellias), should have the offending branch traced back to its point of origin and removed. All these tasks should be carried out in the spring.
PRUNING OF ESTABLISHED SHRUBS
The method and timing of pruning deciduous shrubs is governed by the age of the wood on which flowering takes place: this may be on current season’s growth, or on one-year-old wood or spurs. Evergreens and tender plants are considered separately, and so also is any form of pruning which is carried out for a special effect, such as decorative winter barks.
SHRUBS FLOWERING ON CURRENT SEASON’S GROWTH
Growth has to be made before flowering can take place, so shrubs within this group tend to flower in summer and autumn. If left unpruned, shrubs grow higher but with reduced vigour; moreare produced but these are smaller and poorer in quality. Hard pruning means the removal of a large amount of wood so that the energy of the bush is diverted to fewer shoots and flowers which are consequently larger and of better quality.
Pruning is carried out when bushes are dormant, during the winter months. Weather permitting, mid- to late winter is the best time. All shoots are cut back hard to within two or three buds of ground-level or a framework.
Another method is to cut half the shoots back to two or three buds and the remainder to a half or third of their length. Hard pruning delays flowering but with this treatment the flowering period can be extended and the quality of flowers is still high. The following winter these longer shoots are removed completely, some thinning of resultant shoots is beneficial in spring.
When shrubs of this nature flower in flushes or flower continuously. Dead-heading should be practised to improve their appearance and to prevent them expending energy on ripening fruit. This consists of the removal of the dead flower and if possible two or three buds on the flower stem; cutting is to be preferred, for though some stems can be easily broken off. Others sustain damage to neighbouring buds.
Strong growth and good quality flowers following hard pruning depend on a plentiful food supply, so apply a base dressing of a general fertiliser at the rate of 60-120 g per m2 (2-4 oz per sq yd), the heavier dressing for old and well-established shrubs.
SHRUBS FLOWERING ON ONE-YEAR-OLD WOOD
Growth is made in one growing season and in the following year flowers are produced either on this growth or on short laterals coming from it. This group tends to flower in the early part of the year. Individual shrubs can be pruned directly after flowering, or pruning can be delayed until summer when all the shrubs in the garden falling within this group can be treated.
Shrubs in this group can be left unpruned but they tend to become too tall, encroach on their neighbours or create an unmanageable tangle of growth. Pruning then consists of removing the twigs which have flowered. If young growth is breaking, cut back to where there is a strong young shoot growing in the desired direction. Thin out the remainder of the shoots, especially opening up the centre of the bush so as to improve air movement which will help to ripen the wood. Unripe wood is especially a problem during a wet season when growth is lush. In summer of such a year, carry out a further thinning to help ripen wood. As less wood is removed in the pruning of this group smaller applications of a general fertilizer are required. This can be at the rate of 30—60 g per m2 (1—2 oz per sq yd) annually, or double the rate every second year.
SHRUBS FLOWERING ON SPURS
A spur can be described as a branch, usually a short one, which will produce its flower buds on one-year-old wood but will continue each year to produce more on the same branch; sometimes the wood has to be two years old before flower buds are produced, but new flower buds continue to be added in subsequent years. These shrubs grow strongly in their early years, producing a few flowers, but as growth slows down, so spurs begin to form naturally and there is a reduction of extension growth. At this stage pruning can almost cease.
Their main attraction in the garden is their foliage in the winter months. Most evergreens are liable to damage if exposed to cold winds or subject to prolonged low temperatures. This shows itself by death of branches or the discoloration and death of leaves. Pruning of evergreens is carried out in spring just before growth commences. Cut out any winter-damaged wood, trimming back discoloured foliage; thin and trim to shape. If evergreens are also grown for their flowers, they invariably produce these on one-year wood and so pruning of these is delayed until after flowering.
When grown outdoors, these are always liable to damage by frost, so pruning is delayed until spring when the danger of severe frost has passed. Those flowering on one-year-old wood are not pruned until after flowering. Pruning consists of the removal of winter damage, removal of stalks which have carried flowers and some thinning.
PRUNING FOR SPECIAL EFFECTS
Shrubs are not always grown in gardens for flowers and fruit; sometimes stems or bark or leaves have more appeal.
Shrubs such as(flowering dogwood) or Salix alba (coloured osiers) are planted for their colourful bark during the winter months. Bark colour, is most intense on young wood and the best effect is from the strong young shoots that result from hard pruning. Cornus, and rubus and others with a suckering habit, are cut down to ground-level in spring. Those which do not have this habit are treated rather differently. Several leaders are permitted, each of which is feathered so as to expose the lower part of the stems at an early age.
Many shrubs have finer foliage, either summer or autumn, than flowers. Leaves are only produced on current season’s growth and those of the largest size are on the strongest growth. Deciduous shrubs with variegated, coloured or cut foliage are pruned hard almost to ground-level or to a framework during the winter months and fed copiously.