6 plants you should prune in September, according to experts

This month might feel like a 30-day-long goodbye to summer, but that doesn't mean you should be neglecting your garden – especially when it comes to pruning and cutting back plants ready for the autumn days ahead of us. Say hello, then, to the plants you should prune in September.

From pruning roses and lavender to learning how to deadhead plants properly, it's important to set to work with your shears when a plant's time has passed and it's ready for its next season.

That's why, if you want to keep your outdoor space looking its beautiful best, you need to set up a schedule for pruning and maintenance – tending to the plants you avoid pruning in summer. Because of this September is one of those months you will want to pay extra attention to, as there are a fair few plants that will need cutting back before the colder days settle in...

5 plants you should prune in September

We imagine that, like most proud gardeners, you've likely filled your little oasis with the best garden plants you can – and that you feel a little... well, a little sad about taking your shears to them now summer is ebbing away. Pruning, however, is the best way to a) boost their growth and b) keep them looking spick-and-span.

"In the UK, September is a great time to cut back and prune certain plants and shrubs as the growing season slows down," says Christopher O'Donoghue, co-director at Gardens Revived, who adds that it's his favourite way to prep his plants for winter.

"Whatever you're pruning, be sure to always use clean, sharp tools to prevent disease spread," he adds.

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Christopher O'Donoghue

With almost two decades of experience as a professional gardener under his belt, Christopher set up Gardens Revived with his brother, Andrew, in 2018 to create a thriving family business. Together, they have worked on residential gardens, sites of historical interest, large estates exceeding 70 acres, and award-winning show gardens.

With that in mind, here are 5 key plants you should prune in September...

1. Lavender

If you're lucky enough to have a garden filled with the sweet perfume of purple lavender, it's important to know how to care for a lavender plant, remembering to stick it on your list of plants to prune in September (or whenever the flowers start to fade).

"Cut back hard to a good compact shape but be sure to leave some new shoots on each stem – lavender will often not regrow from bare wood," advises Monty Don via his popular gardening blog.

"These new shoots will grow fast and provide an attractive and healthy cover to protect the plant in winter and provide the basis of next year’s display."

2. Herbaceous perennials

From delphiniums and geraniums right through to hostas, Christopher counts herbaceous perennials among the plants to prune in September.

"You'll want to cut back dead or dying foliage and stems, and tidy them up as they begin to die back for the winter," he explains.

Don't be afraid to give these plants a good hard trim, taking them right down to the ground if needs be – the main thing you need to preserve, after all, is the crown (base of the plant), which will remain dormant over winter ready to produce fresh shoots come springtime.

"You can leave the ones with decorative seedheads in place for wildlife to enjoy, though," adds Christopher.

3. Shrub roses

One of the most alluring plants around, Christopher says that September is the best time to tidy up your shrub roses and encourage them to focus on strong, healthy growth for next season.

However, while he suggests a 'light prune and deadhead', Monty Don states that you should "not worry about the position or angle of the cuts but clip away all long, straggly shoots as though you were trimming a hedge, leave a compact, slightly domed bush that is about two-thirds of its former size".

4. Summer-fruiting raspberries

Anyone who has started vegetable gardening for beginners will likely have branched out (ha!) into fruits as well at some point – and raspberries, being among the easiest to grow, are usually at the top of most people's 'Grow Your Own' list.

Here's the thing, though; summer-fruiting raspberries are among the plants you should prune in September (along with other soft and bush fruits like blackcurrants, gooseberries and redcurrants).

'Cut back the old fruiting canes that have fruited this year, leaving the new ones to develop for next year’s crop,' advises Christopher, who says this is the best way to encourage next year's fruit and keep the plant healthy.

It's a good idea, then, to tie the remaining canes to some support, such as this MRGARDEN Raspberry Trellis and Stake Vineyard Trellis from Amazon.

5. Yew hedges

As per the RHS, a yew hedge can grow vigorously – up to 30cm a year. To that end, then, it's vital you prune it at least once a year, and early autumn is an ideal time to do it if you want it to look crisp and fresh for the colder months ahead.

"The idea is to give it a final trim before winter," says Christopher. "Go in with the aim of maintaining the hedge’s shape and preventing it from becoming overgrown before the dormant season."

Just be sure to check your hedge before you set to work, and delay if you find an active nest (it is a criminal offence to disturb nesting birds). And, of course, be sure to wear protective gardening gloves as yew is highly poisonous.

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6. Jasmine

Much like deciduous honeysuckles and passion flowers, jasmine is one of those climbing plants you should prune in September – ideally just after they've finished flowering.

As well as thinning out any overcrowded or damaged shoots, the RHS advises that you 'cut back flowered stems to a strong side-shoot lower down' to give new growth time to mature and flower early next season.

FAQs

What plants need pruning in September?

If you want to know what plants need pruning in September, aim your pruning shears at the following:

• Lavender and other Mediterranean shrubs (such as rosemary)
• Yew and other evergreen hedges (such as cypress and box)
• Raspberries and other soft or bush fruits (such as blackcurrants and redcurrants)
• Shrub roses
• Herbaceous perennials (such as delphiniums, geraniums, and hostas)
• Jasmine, common honeysuckle, and passion flower

"It’s important not to prune too late into autumn, as fresh growth stimulated by pruning might not have time to harden before the first frosts," advises Christopher O'Donoghue of Gardens Revived.

Is it okay to trim hedges in September?

If you're wondering if it's okay to trim hedges in September, there are two things to consider; are there any signs of nesting birds, and what kind of hedge is it?

It is, of course, an offence to disturb birds that are nesting, so if you find your hedge has become home to a family of feathered critters, pop your shears down and wait until they've vacated the area.

Once that's been established, yew and other evergreen hedges (such as cypress and box) will benefit from being pruned in September and early autumn.

"Always take out any dead, diseased, or damaged wood to promote the health of the plant," says Christopher O'Donoghue of Gardens Revived.

Now that you know the plants you should prune in September, it's time to set to work trimming and tidying everything up ready for the next big season to protect your plants from frost.

You'll be glad you put the work in once the first frosts roll around, trust us...