4 plants you should never prune in December – and why pruning in winter could cost you next year's blooms

Pruning is a popular winter gardening task, but we thought we'd take a look at the plants you should never prune in December to ensure we aren't dealing our trees and shrubs undue damage.

Thanks to the dormancy period, there are plenty of plants you can cut back in winter, which means there are several plants to prune in December. For others, winter pruning can remove potential flower buds, leave plants vulnerable to disease and stunt spring growth, so it's crucial that you know which plants to avoid trimming this month.

Pruning rules aren't always straightforward, and even within our list of plants you should never prune in December, there are a few exceptions – but we'll delve into those shortly.

1. Lavender

Of all the plants you should never prune in December, lavender is one to watch out for. Pruning at this time of year can seriously damage or even kill a lavender plant, so knowing when to cut back lavender, and when not to, is key.

'Lavender is sensitive to excess moisture, making it vulnerable to winter pruning,' explains Emma Fell, head of horticulture at Hillier Garden Centre and Nurseries. 'Trimming lavender in winter can expose its raw stems to cold and damp conditions, increasing the risk of rot.'

Winter pruning also runs the risk of removing any potential flowers.

'Pruning in winter will cut off the buds that would have opened in spring and diminish the plant's overall health,' Emma says.

Instead, wait for your lavender plant to finish flowering in late summer before you give it a trim.

Emma Fell

Throughout her career, Emma has been responsible for sourcing and selecting new plants, including the ones that feature in Hillier's illustrious show gardens such as at RHS Chelsea and BBC Gardeners' World. Her role as head of horticulture means that she ensures Hillier Garden Centres continue to offer customers' the highest quality of plants for their gardens, as well as exciting new varieties, both from Hillier Nurseries and other British nurseries.

2. Forsythia

Knowing when to prune forsythia is crucial, because cutting the shrub back at the wrong time can spoil the blooms-to-be. That's unless you plan on renovating a forsythia shrub, which can be carried out during winter at the expense of the following season's flowers.

'While it may be tempting to shape or reduce its size during winter, forsythia benefits more from pruning immediately after flowering,' says Emma. 'Pruning in late winter can remove potential flower buds, diminishing its spectacular spring display.'

So, hold fire until after the shrub has finished flowering in spring for the best results. Other spring-flowering shrubs like lilac fall under this guidance, too.

'When it comes to which plants you should never prune in December, I’d say early flowering shrubs and plants are best left alone,' agrees Hannah Rowson, assistant garden centre manager at plants and bulbs specialists J. Parker’s. 'These are already forming buds for their spring blooms, and pruning now could ruin their display.'

3. Hydrangeas that bloom on old wood

Guidance around when to prune hydrangeas varies because there are so many different varieties, but several types make our list of plants you should never prune in December.

It all comes down to whether your hydrangea blooms on old wood or new wood – and if your plant blooms on old wood, winter pruning is best avoided.

'If your hydrangea blooms on old wood, like mophead and lacecap types, it’s best to avoid pruning it in winter as it may remove potential flower buds,' Emma explains. 'Instead, wait until after the plant has bloomed.'

Hydrangeas that bloom on new wood like Paniculata varieties can tolerate winter pruning, but it's still better to hold on for a little while longer.

'Removing too much now can expose the buds to frost damage, so if you do prune, focus only on damaged or dead stems while leaving the old flower heads intact for added protection,' says Hannah.

4. Stone fruit trees

If you've been wondering when to prune plum trees, peach trees and other stone fruits, you'll want to hang fire until winter is over, because these are stellar examples of plants you should never prune in December.

Stone fruit trees are more vulnerable to disease in the winter, and pruning can increase the risk of infection.

'Plum trees in particular are susceptible to silver leaf fungus,' explains Gareth Mitchell, founder of Tree2MyDoor. 'The spores are released in autumn and winter when the weather is damp and can kill an infected tree.'

Rules around when to prune apple trees and pear trees are a little less strict. In fact, December is a great time to prune them.

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FAQs

Should I cut back perennials in winter?

Herbaceous perennials are generally cut back in autumn after they have finished flowering. What's left of the plant will remain dormant for the rest of winter, bursting into fresh growth in the spring.

Leaving some of the stems or seedheads over winter is a fantastic wildlife garden idea, providing shelter for insects and small animals.

When should you avoid pruning?

Even though some plants can be pruned in winter, keep the secateurs locked away on frosty days. Pruning during freezing weather can actually damage the plant. Instead, take the time to learn how to clean your garden tools or sharpen your secateurs.

Now you know which plants you should never prune in December, you can be sure that you aren't hindering next year's growth.