6 plants you should prune in September, according to experts
You must set aside some time to prune these garden plants this month
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 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...
6 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 that 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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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 add it to 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
Garden with hostas and other 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 need 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. Supporting plants as they grow will keep them in good health and ensure they can withstand the weight when fruit starts to develop.
5. Yew hedges
As per the RHS, a yew hedge can grow vigorously – up to 30cm a year. To that end, 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 to maintain the hedge’s shape and prevent 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.
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, put 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.
What should you not cut back in September?
Whilst there are lots to get pruned during September, there are several plants you should never prune in autumn.
"Spring-flowering shrubs, like hydrangeas, should not be cut back during September. These plants form flowers on old wood, so cutting them now runs the risk of removing future flowers. For plants like hydrangeas, leaving the faded flowerheads in place can help to protect the plant during frosts," explains Richard Barker, horticulture expert and Commercial Director at LBS Horticulture.
He also recommends against pruning trees with heavy sap, which will bleed heavily if they are pruned during September. "Weeping sap like this weakens the tree and makes it more vulnerable to bacterial or fungal infections, so it is best to prune in winter when they are fully dormant," adds Richard.
And whilst your roses might look like they need pruning, a heavy chop can cause more damage than good. Richard says, "This is because it can trigger tender growth that is vulnerable to frost damage and disease."
With 4 years in the industry, Richard is a gardening expert at LBS Horticulture. He is keen to share his knowledge with both experienced and beginner gardeners, and prides himself on keeping up to date with the latest horticultural trends.
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 and to protect your plants from frost.
You'll be glad you put the work in once the first frosts roll around; trust us...
