PRUNING 1 - WHY PRUNE?

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Ask many gardeners why they prune their shubs (and climbers) and they will tell you it’s because they have got too big. But this is not the plant’s fault – it’s been planted in the wrong place or too close to its neighbours. The real reason is so the plant performs better. Some things don’t need pruning. For example daphne mezereum makes a round shape with well-placed growths but others, like a buddleia, become a huge mass of old and jumbled wood, flowering right at the top almost out of view. Some things respond well to being cut back – mahonias sprouting from just above a leaf joint – while others, notably most conifers but also the witch hazels, will not break from pruning cuts. Experience or a good gardening book will tell you whether to prune and what results to expect.

So what are we looking to achieve when we get out the secateurs? The first thing to look for is any dead or diseased wood; this is the first to take out. Next on my list is air flow. Stagnant air in and around a plant encourages disease; a plant with an open centre allowing good air circulation is less prone to problems. So I remove any shoots growing towards the centre of the bush or crossing branches, always pruning to a bud in the direction of the growth I want to encourage. We want to encourage flowers or fruit or maybe stem growth if the young wood has coloured bark. Removing old wood encourages the plant to ‘make good’ the ‘damage’ by making new growth which is more prodctive than old, tired branches (but in the case of fruit trees, we are trying to increase the number of fruiting spurs consistent with what the tree can carry without exhausting itself). Take your time and think about each cut – as my father once said, “There’s no such thing as a putting-on saw, only a taking-off one.” The finished result should be a well-shaped plant with an open centre. Cutting to shape or reducing the size I call “cosmetic pruning” – it has its place but don’t think of it as just a hacking-back job. Yesterday for example, I reduced the spread of the lower half of a large skimmia but left the upper half intact; now it doesn’t look to have developed middle-age spread but still has a natural-looking outline. Some shrubs, such as pyracantha, do not form a good shape and will throw branches in all directions; removing some of these completely will improve their appearance.

Wall-trained plants need slightly different attention – here the process it to retain a plant growing parallel to the wall rather than towards or too far way from it (although many shrubs, including ceanothus, will gradually increase in girth over the years and trying to limit this usually means removing the wood to carry the next crop of flowers). Topiary (and hedge-trimming) is an artificial form of pruning where the shape of the resulting plant is the raison d’etre. And finally, don’t neglect to cut out any growths on variegated plants that have reverted to green; they contain more chlorophyll than the other shoots and, if left, will take over.

• 30 Jan, 2008
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