One of the certainties of the gardener's lot is there’s always a plant that needs pruning. No sooner have you finished winter pruning than a clutch of evergreen shrubs need attention. What follows here doesn't apply to conifers, as they need little pruning and only grow from fresh wood.
When the worst frosts are over, die-back is less likely and growing plants will heal quickly. They’ll grow away strongly, repair wounds and reduce the risk of infection, while fresh foliage will conceal any pruning scars. So try devoting time to pruning your shrubs, even when there’s so much else to do in the garden.
Start by removing any dead or diseased branches. If you’re growing a shrub for variegated or silver foliage – such as santolina or brachyglottis – remove any shoots producing plain-coloured leaves.
This is also a good time to trim evergreen holly, yew or box hedges to make sure they don’t get out of hand. Generally light pruning is best for evergreens. And, where possible, use secateurs and loppers not shears, as half-cut leaves turn brown and look unsightly.
Pruning in April and May encourages bushier, more compact growth. The main growing stem of a plant enjoys what is known as apical dominance, soaring to the heavens by releasing hormones that prevent side shoots from growing as vigorously as they otherwise would. Removing the main stem therefore encourages side shoots to grow strongly.
This also apples to side branches: several narrow stems emerge when a branch is cut back. Removing a leading shoot allows lateral buds to develop.
Pruning now lets you direct a plant’s growth. Remove branches or stems that are growing too high, towards a wall or are about to smother a neighbour. The shrub then puts its energies into growing in the direction you want.
As a general rule, cut an offending stem or branch back to its join with the main stem, not half way along a branch. The remains of the branch will either die and look hideous, or will sprout a cluster of little stems. Choose carefully where to cut.
But life isn’t always that simple. If a shrub has got out of hand the challenge is deciding what to do and how deeply to cut. When pruning an overly large shrub, bear the root-to-shoot principle in mind. Plants try to balance the volume of root with top growth. Foliage provides energy to the roots through photosynthesis, while the roots supply the rest of the plant with water and nutrients.
A large shrub will have an equally big root system, so hard pruning will encourage roots to compensate for this by stimulating a mass of small shoots. You could find excessive pruning counterproductive. If you have a weakly specimen, try a kill-or-cure approach. A massive cutback could shock the plant into growth and it would be no loss if the poor thing died.
Some shrubs can tolerate hard pruning better than others. To check whether your plant is up to it, see if there is any sign of small tufts of leaves below where you want to cut. If so, it should be safe to prune to 5cm above the leaf buds. Mahonia x media should respond well to this treatment. But you can only thin the stems, removing no more than one third at one time. No plant can regenerate itself with only five or six little tufts of leaves.
In the same way, repeated hard pruning may exhaust the roots and kill the plant. So only wield the loppers once every few years.
You might get away with even more drastic pruning of tough specimens like elder, providing you do it once in a shrub’s lifetime. And to give it the best chance of surviving such an ordeal, feed and mulch the plant, taking care to water it during a dry spell of weather.
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