© Gap Photos/Howard Rice
"Dig a little deeper, and you invariably find that the person was pruning the plant at the wrong time of year. If you prune a summer-flowering shrub in April, you are effectively cutting off the year's flowers. So pruning at the right time is crucial," he says.
In Wilson's experience, people are scared of pruning but he points out that, provided the plant isn't very young, sickly or old, you are unlikely to kill it.
"Even if you prune a plant badly, the plant's natural reaction to being cut back is to grow more. And it's invariably better to prune an overgrown shrub, restoring its vigour, than to leave it to grow even larger and more ungainly," he says.
Wilson makes a clear divide between aesthetic and horticultural pruning. He says: "With aesthetic pruning, you are creating a special effect, like pad and cloud pruning, which is cutting 'clouds' into shrubs such as Ilex crenata, leaving bare stems. Topiary comes under this category too. You can achieve a huge amount in a shady garden by crown lifting trees and shrubs; removing side shoots to let in light.
"Then you can improve the vacated soil beneath, and plant groundcover such as geraniums and bergenias. A lot of established shrubs, particularly old roses and viburnums, have fantastic character in their framework and you can get a wonderful effect of looking through the stems by dramatic crown lifting."
Most shrubs, says Wilson, can take drastic pruning. He adds: "I've cut a massively overgrown Viburnum tinus to ground level with a chain saw because I wanted the shrub to have leaves and flower down to the ground, and within two or three years it regenerated, giving me just the effect I wanted.
You can prune most plants hard — doing it in stages is a good idea — but you must always put something back at the end, feeding the roots around the base of the plant and watering well if the ground is dry."
With horticultural pruning, people are scared of cutting too much, not enough or at the wrong time. "At least a couple of times a year I get asked, 'I've got a lovely big Bramley apple tree, and I don't know how to prune it'. My answer is: 'Why would you want to?'
© Gap Photos/Jerry Harpur/Design by Tom Stuart Smith
You don't need to hack back a beautiful Bramley, but I've got espaliered apple trees trained along my garden boundary so I have to prune them or they will lose their shape and revert to fruit trees. If I had a vine, I would prune, in order to make the vine produce bunches of grapes, otherwise after two or three years it would have less vigour and be less productive. You have to apply common sense."
We make most mistakes when pruning roses. Wilson says: "People confuse the pruning regimes of hybrid teas and floribundas with shrub roses, and hack down their David Austin roses to three buds in February, but these only need minimal pruning. David Austin, after all, spent 50 years creating roses that have a beautiful shape.
"Hybrid teas and floribundas, on the other hand, should be cut back hard; you can identify these by their sprays of flowers on long stiff stems, like cut flowers. Shrub roses have a looser growth, with lots of side shoots."
The three Ds apply to all pruning, including roses, points out Wilson. "Always remove any stems that are dead, damaged or diseased. Your aim is to preserve and enhance the shape, making it less bulky, thinning it out. By opening up the centre of the plant, you improve air circulation and thus reduce pests and diseases.
"At this time of year, I reduce any long, whippy stems by about half to prevent them breaking off in winter winds and to discourage wind rock, which damages the root system. In February, I main prune my roses, as well as any plant that puts on excess growth in summer, such as lavatera, buddleia and cotinus."
Wilson's most valuable piece of pruning advice? "Be brave, and keep your secateurs sharp. Stand back and look before you do anything. Don't try and change the plant into something different if the natural shape is good; go with the flow."