But pruning goes much further, as gardeners over the centuries have sought to shape plants into attractive or, dare I say, ridiculous forms. Many gardeners have found topiary irresistible.
Even so, they have had their critics. In 1712, Joseph Addison wrote: "Instead of humouring Nature, [gardeners] love to deviate from it as much as possible. Our Trees rise in Cones, Globes and Pyramids. We see the marks of the Scissars upon every Plant and Bush." He might have preferred the modern, hands-off style of gardening.
But a garden is a controlled space and even in the most wildlife-friendly one, it's worth adding a more formal element that will make an eye-catching statement. Pleaching is a pruning method that does just that; a technique where stems and branches of neighbouring trees are intertwined and grow together to create attractive designs.
There have been different styles of pleaching, or plashing (possibly from the old French for plaiting). In the 16th and 17th centuries, pleaching as we know it started, especially in France and Italy. It was labour-intensive, so was ideal for any landowners keen to flaunt their wealth. Requiring a large squad of gardeners, pleaching showed money was no object for the owner.
Limes - especially the red-twigged lime, Platyphyllos "Rubra" - and hornbeam were normally used for pleaching, but ash, beech, chestnut, apples and pears were not unknown. I've even seen quick-growing but horribly prickly hawthorn at Melrose Abbey.
Trees were used to define walks. A temporary frame, comprising vertical tree stakes linked together with three or four horizontal poles or wires, was built. The trees were planted two metres apart in straight lines. When three or four years old, each tree's whippy leader was bent horizontally in one direction, with a side stem trained in the other direction. Lower branches were tied to the other horizontals and wrongly facing branches and buds removed. The aim was to encourage the selected branches to meet and intertwine with their neighbours to form a long, elegant line. Leaving enough space for a walkway, a second parallel line was planted.
These grand walks or allees fell out of fashion in the second half of the 18th century, only to be revived in 1822 by Sir Walter Scott. In The Fortunes Of Nigel, Lord Huntingdon tried to calm his companions by proposing a soothing and diverting "turn in the pleached alley". Predictably, the Victorians later fell upon these grand pleached allees and often used them to divide and define parts of their kitchen gardens.
A few good examples of this style can still be seen in Scotland. The gardens at Portmore Lodge, near Peebles, include a pleached lime walk. The garden opens for Scotland's Gardens Scheme every Wednesday in July and August. The gardens of Glamis and Crathes castles also feature pleached walks.
Walkways like this have year-round appeal. I reckon they come into their own in winter and early spring when, stripped of leaves, their skeletal beauty stands out. This pruning technique is now used in many ways, with trees trained to form ceilings, tunnels and arbours. For me, the most impressive is in Switzerland - a hornbeam's perfect sphere overlooked by Lausanne Cathedral.
You could consider a smaller version for your garden. Use a low-growing pleached hedge to define a potager, a flower garden or a wildflower plot. Choose the sunniest spot for an arbour or create a tunnel to link two areas. If you're patient and enjoy creating things, start with young saplings, or if you want immediate effect and can afford it, buy trained specimens from a specialist nursery.