How to keep a shrub healthy

This involves the removal of weak, damaged, dead or over-crowded shoots. In this way potentially damaging decay fungi which gain entry to weak shoots, etc, can be prevented from growing back into the healthy ones, and the number of places where damaging insects can hide can be reduced. This aspect of pruning would include prompt action to remove a dying shoot which shows during the growing season. When cutting out diseased material, always make the cuts into sound or healthy wood well beneath the diseased portion which should be promptly burnt. With some diseases, eg Fireblight and Dutch elm disease, the organism responsible is likely to have penetrated some distance below the obvious signs and removal of the branch from its point of origin is advised. When cutting diseased shoots, it is good practice to sterilise the knife or secateurs used by wiping them on a rag soaked in methylated spirits, ideally after each cut. This will reduce the chance of transferring the cause of the infection to a new branch or plant next time the tool is used.

 

Controlling or reshaping a shrub

Many of the more vigorous shrubs will grow into small trees or become very wide spread­ing with time. They therefore need pruning to keep them within the space allotted or to rejuvenate an old plant.

 

The technique for reducing the spread of a shrub is similar to that for trees in that too great a reduction will lead to excessive regrowth, defeating the objective. If a branch extends too far in one direction, it can either be reduced to a suitable crotch (see ‘drop-crotching’ above) or should be removed from the base. Indiscriminate hacking back will usually give a mediocre result of a tangled mass of leafy new shoots.

 

An overgrown shrub can be rejuvenated by cutting it back either to ground level or to low down on the stem. Most, but not all plants, will coppice or regrow following this treatment and will make useful plants in less time than if a new specimen is planted. Subjects where this is a useful technique include lilac (Syringa) and mock orange (Philadelphus) but it can also be used on overgrown plants of buddleia, holly, corylus, yew and other similar large shrubs. It will not work on conifers (there are rare exceptions) and many evergreen shrubs do not respond that well, eg hebes and camellias may some­times fail to regrow. If a large shrub is in poor health, cutting it back may rejuvenate it but where the plant is diseased, eg at the roots, it will often fail.

 

Suckers from the roots are a natural feature of many shrubs, eg Rubus cockburnianus, but in species which are propagated by grafting onto a rootstock, they will be growths from the rootstock. If they are left, they will often be more vigorous than the choice plant and swamp it. They should be removed from the lower stem or root system where they origi­nate; cutting them off at soil level will only encourage their proliferation. The simplest method is gently to force a spade down between the stem and the sucker until it is in the crotch and then to pull the sucker with one hand and lever the spade away from the stem with the other.

 

Variegated plants will (often produce patches where there is no variegation, just plain green foliage. As with suckers, these must be removed before they dominate and ruin the plant.

Pruning to enhance attractiveness

 

There are several different ways to prune shrubs. The variations between the tech­niques of pruning are primarily related to the season or timing of the operation and the type of wood on which the desirable charac­teristics of the plant are displayed. Which technique is appropriate depends upon the growth characteristics of the particular shrub and also upon what is desired of it. Similar plants in one genus may require very dif­ferent pruning regimes to flower to best effect, eg different buddleia and clematis. The first requirement is to know which species you have and when it will flower. If you are not familiar with a plant in a newly acquired garden, it often pays to wait and see what it does before pruning.

 

The simplest group of shrubs to prune are those which flower in late summer on the current season’s growths, eg Buddleia davidii, caryopteris, Clematis tangutica, C. jackmanii, fuchsia, hypericum and indigofera. These plants can be cut back to old wood in late winter or early spring and most will give larger or more strongly coloured flowers than if left unpruned. All the flowering plants in this group will give a display without pruning and this will be earlier in the season than occurs on pruned plants, although the plant’s habit may not be as attractive.

 

Plants grown for the effect of the winter bark of one-year-old twigs, eg Corn us alba, Rubus cockburnianus and Salix alba ‘Chermi-sina’, or for bold summer foliage, such as coppiced plants of ailanthus, paulownia and Cornus alba ‘Elegantissima’, will produce longer and more brightly coloured twigs or larger leaves than unpruned plants. These too should be cut back bard in late winter.

 

Many plants flowering in the early part of the season, usually up to late June, do so from flower buds laid down during the previous summer. Examples are Buddleia alternifolia, B. globosa, Clematis montana, Rosa species and rambler roses. With these, it is disastrous to prune them hard in late winter, as all the coming season’s flowers will be thrown away. They should be pruned as soon as flowering has finished. Pruning will entail the removal of the shoots which have just flowered so that vigorous young shoots can replace them and develop next year’s flowers. Pruning of these plants should not be severe. Also, with several plants, eg specie roses and Berberis x stenophylla, the fruits are an attractive part of the display, and this aspect will be lost by pruning.

 

Similar to the above group are many shrubs which, whilst flowering on the pre­vious year’s growth, produce most flowers on short spur growths off two-year-old shoots. Examples include deutzia, forsythia, kolk-witzia, philadelphus, ribes and weigela. In these plants, the pruning needs to be carried out on a three-year cycle. After flowering, the two-year-old shoots are removed and the current year’s shoots selected to replace them; this will usually involve thinning out the number of current and previous and one-year-old shoots.

 

Many smaller evergreen plants do not respond to any pruning or are rather touchy. These include items such as cistus which can only be pruned when young. Brooms, such as cytisus, genista and spartium, and most conifers, such as chamaecyparis and x cupres-socyparis, can only be cut back into wood which is still green; if you cut into old wood, the plant will die back. These items can only practically be pruned to retain a shape.