Ever wondered when not to prune trees? You should! After all, pruning might be one of our favourite garden jobs (anything that feels productive, eh?), but you can do a lot more harm than good if you whip out the loppers at the wrong time.
Yes, just as there are some plants you should never prune in autumn, there are plenty of other things to take into consideration when you’re cleaning your garden tools and sharpening your secateurs. Primarily, the when of it all – because, yes, there is such a thing as a ‘wrong time’ when it comes to pruning trees, as it ‘could damage the tree,’ says Morris Hankinson, Managing Director of Hopes Grove Nurseries.
‘It’s important to know what your tree is and when to prune it – or perhaps more importantly, when never to prune it,’ he adds. And so, with that in mind, here are the key times of year and conditions when the shears should stay firmly in the shed…
1. During spring sap rising
Between February and April, trees “wake up” and start pumping energy into fresh shoots, leaves, and buds. If you prune over this period, Morris warns, you’ll divert all that energy into healing wounds instead.
‘Sap bleeding can weaken the tree and increase the risk of pests and diseases at this time of year,’ he says, noting that this is a prime example of when not to prune trees.
2. During bird nesting season
Trees, hedges, and shrubs are vital nesting sites, and it’s actually illegal to knowingly damage or destroy a nest in use under Section 1 of the Wildlife and Countryside Act 1981.
‘Double check before pruning, or simply leave it until another time, especially if you can’t access dense hedging,’ advises Morris, who notes that this usually means you won’t be able to prune between March and August.
Writing on his own blog, Monty Don agrees, noting: ‘Young birds will have left their nests by the end of the [summer] so hedges can be safely cut. A trim now will allow any subsequent regrowth to harden off before possible autumnal frosts.’
3. Evergreens in winter
Evergreens earn their keep in the garden during the bleak months, but they’re at their most vulnerable then, making this a great example of when not to prune trees.
‘If pruned in winter, evergreens are more susceptible to winter damage, and open wounds can cause water loss, especially in dry winters,’ says Morris. Wait until early spring for these.
4. In wet or extreme weather
It’s not just the season that matters, but the conditions. ‘Wet weather can transfer bacteria or fungi to fresh pruning wounds,’ Morris explains. ‘And extremely hot or dry weather can cause unnecessary stress.’
Christopher O’Donoghue of Gardens Revived agrees, noting that it’s also important to avoid pruning if frost is forecast within the next three days. ‘If a cold snap hits just after you’ve pruned, it means the cut ends won’t have time to dry and seal,’ he explains.
Always wait, then, for a settled spell.
5. Just before flowering
If you’ve ever wondered why a tree didn’t bloom, your pruning may be the culprit; buds often form weeks or even months before flowering.
‘Don’t prune off flower buds, as that will most likely mean no flowers for the growing season, which would be such a shame!’ Morris says.
Instead, consider this another example of when not to prune trees, and wait until the flowering period is over.
6. Deciduous trees in late summer
Late summer to autumn is when deciduous trees are storing up energy for next spring. Pruning at this stage means they can’t make enough food, and any new shoots won’t harden off before frost arrives.
‘Leaves produce food for the tree, so if they are pruned now, trees won’t be able to store the energy they need,’ Morris explains. The best window for pruning is late winter to early spring.
FAQs
When should trees not be trimmed?
If you’re wondering when trees should not be trimmed, the RHS is clear on this: avoid pruning when trees are actively growing in spring, because that’s when the sap is rising and they’re pushing all their energy into new shoots and leaves. You’ll weaken the tree and risk sap bleeding.
‘Same goes for late summer into autumn with deciduous tree, as that’s when they’re storing energy for winter,’ says Christopher O’Donoghue of Gardens Revived.
‘Take away too many leaves then, and you’re robbing them of the food they need to get through the colder months. And of course, March to August is bird nesting season, so you don’t want to be disturbing wildlife either.’
Is October too late to prune?
Is October too late to prune? Well, that really depends on what you’re pruning. ‘For most deciduous trees, yes, October is too late. By this point, the tree’s winding down, drawing energy back from the leaves into the roots and stems ready for next spring,’ says Gardens Revived director Christopher O’Donoghue.
‘If you cut then, you’ll take away that stored energy and any new shoots won’t harden before the frosts. If it’s a light tidy of dead, damaged, or diseased wood, though, you’re fine, as that can be done anytime.’
Essentially, for structural pruning, shaping, or cutting back hard, Christopher says you’re better off waiting until late winter or early spring when the tree’s dormant. ‘That way the wounds heal faster, there’s less risk of infection, and you’re not stealing the tree’s reserves,’ he explains.
Pruning at the wrong time stresses trees, leaves them open to disease, and can even break the law during nesting season. But get the timing right, and your trees will reward you with healthier growth, better shape, and (depending on the tree!) more blossoms, too.
That’s more than enough reason to do your research, we say!
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