With summer shifting into autumn, thoughts turn to the selecting the right plants to prune in September. It's the ideal time for targeted pruning of plants and flowering shrubs to keep them healthy, vigorous and growing well. It's an easy process that means removing any dead, damaged or lopsided twigs and branches to allow the plant to be in the best shape possible for winter.
Many deciduous varieties can be pruned at any time during the dormant season, roughly from now until February depending on climate variations. Once plants lose their leaves, their shape is revealed and it’s easy to see what needs to go to improve their overall look. Thinning out any densely packed stems lets in more light and air to benefit the health of the plant too.
Remember that many shrubs and climbers have spectacular autumn leaf colour and berries to enjoy before you start snipping as part of your September garden jobs. Once the display is over it's a good time to get the secateurs out.
1. Wisteria
If you're lucky enough to have a wisteria in your garden design, the gorgeous blooms it was covered with back in spring and early summer will be a distant memory. So it won't be the first thing that springs to mind when it comes to plants to prune in September. To get the best out of your wisteria, however, it needs any wispy growth pruning now to prevent your plant becoming overgrown.
"For the best results, give your wisteria a prune twice a year," says plant expert Helena Jones. "Once in August/early September to tidy things up and to let sunlight reach next year's flowering wood, and again in winter to encourage plenty of short, flowering spurs. Just cut back all the strong new growth to five buds and remove any spent flower stalks from this year."
Wisteria won't bloom as well unless the vigorous leafy summer shoots are cut back in late summer to encourage your plant's energies into more bud production next year.
Before you start any pruning, make sure you sharpen your secateurs or any other pruning tools you are going to be using so you can make the cleanest of cuts.
Helena Jones is currently head of commercial at Hedges Direct Limited, having been in the business since 2022. Her expert knowledge of the product range, and horticulture in general, helps Hedges Direct continue to be the online market leader.
2. Climbing honeysuckle
Climbing honeysuckles don't need a lot of pruning to be covered in flowers but if you neglect to prune them the heart of your plant will become congested with a mass of tangled, woody stems that ultimately means you'll get flowers only on the tips of the stems. Honeysuckle makes it on to our list of the best climbing plants for pergolas but it's not much use if it's so in need of a prune you can't see any of the flowers.
Honeysuckle is one of the key plants to cut back in September and it's the ideal time to tackle restorative pruning, especially if you forgot to renovate your plant in spring. Most honeysuckles are deciduous and are best pruned after flowering during late summer/early autumn, except for evergreen Japanese honeysuckles which should be pruned in early spring.
"The long, trailing stems of deciduous honeysuckles can be shortened to three or four leaves. Take older stems out down to the ground to promote new growth and avoid a ‘bare bottom’," says Helena Jones. It's a good idea to reduce the number of main stems and take out any crossing branches too, as this will free up the heart of the plant.
3. Common jasmine
Common jasmine (Jasminum officinale) is another scented climber that will benefit from being pruned in September after flowering has finished. Although it's great for garden screening, this variety puts on so much summer growth it can become completely overgrown by September.
You will need to prune carefully as next year's flowers will already be forming on the older wood and you don't want to damage them, so aim to snip back the new growth on the tips of the plant instead. It's fine to prune back hard if the plant needs rejuvenating, cutting back any diseased stems to a healthy section of the plant, and aiming for well-spaced stems.
Alternatively if you're simply tidying up a newer plant, cut back overgrown stems just above the leaf joint. Once you've pruned back you can tie in what's left to create a new framework for the plant so it will look its best next year.
Common jasmine is not to be confused with the other popular variety star jasmine (Trachelospermum jasminoides), which is best pruned in spring.
4. Climbing hydrangea
As one of the best climbing fence plants, climbing Hydrangea petiolaris varieties should be pruned immediately after they finish flowering, which is generally at the end of summer and most likely in September. They are not to be muddled up with the other hydrangea varieties paniculata and macrophylla (also known as mophead and lacecap hydrangeas), which are pruned in spring.
Trim any wayward stems and shoots from climbing hydrangea as part of your general tidy up of plants to cut back in September, as skipping this stage can lead to a poorly shaped plant and less prolific blooms next year.
Most flowers are produced towards the top of the plant, so try not to touch these sections, instead concentrating on thinning out side branches and reshaping the plant for a better structure. Remove all the faded flowers as you go as part of your September snip.
5. Rambling rose
Pruning rambling roses is one of the best things you can do to improve their shape, structure and help them flower more profusely in summer so your garden walls are covered with blooms. As with pruning any type of rose you'll need a good pair of gloves, some twine for tying in and a sharp pair of secateurs. Prune ramblers in late summer, which means it's one of the key plants to cut back in September.
The first thing to consider is how old your rambling rose is. New ramblers flower for a couple of years without any formal pruning necessary. But once established they produce lots of growth from the base and if not carefully trained will become unmanageable. So the older your rambling rose is the more important it is to maintain its framework.
The main consideration is to prune back side shoots, removing any weak or diseased stems, as well as any dead sections. Then train in the new shoots. Always keep the overall shape of your rambling rose bush in mind. Following these easy steps will lead to new growth and flourishing rose production for years to come.
Pruning times differ for other types of roses such as climbing roses and shrub roses, as many varieties of these are repeat flowering and you won't want to remove buds.
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6. Lavender
Certain evergreen aromatic plants, such as rosemary, sage and lavender, as well as other Mediterranean shrubs and herbs are definitely on the list as plants to prune in September.
"Sun-loving shrubs such as lavender and rosemary should be cut back in September as they will not tolerate hard pruning in winter," says horticultural expert Richard Barker from LBS Horticulture. "Cut these plants back after flowering, but avoid trimming old wood as this can kill the plant."
Ideally, lavender should be pruned twice a year, once in September followed by a tidy-up in spring to keep your plants healthy, with a good show of flowers in summer. Leave the woody base of the plant well alone, and instead trim stems in late summer after they finish flowering.
Whether you grow your lavender in the ground or in pot as part of your garden planter ideas, cut stems leaving about 2-3 inches above the woody base. Gather handfuls of stems at a time to make it easier, with the aim of creating an attractive rounded shape for what's left of the bush. Any dead or diseased branches should be completely removed, and this will let air into the heart of the plant too.
Richard Barker is an expert in horticulture and the commercial director at LBS Horticulture. He is keen to share his knowledge with both experienced and beginner gardeners, and prides himself in keeping up to date with the latest horticultural trends.
7. Fast-growing evergreen hedges
Generally evergreens need very little pruning once established and this is usually done in spring or after flowering. But there are exceptions, such as evergreens used for hedging, which can quickly become unkempt. It's best to prune fast-growing hedges twice a year to keep them looking smart.
"Evergreen hedges can be trimmed in September to make sure they're tidy for winter, especially if they're fast-growing varieties," says Richard Barker. "Ideally, cut hedges slightly narrower at the top, as this will make them less vulnerable to snow damage and stop them from shading themselves out at the base."
Varieties of evergreen hedging like yew and cypress should be pruned in late summer or early autumn when the new growth for the year has finished.
"Unless you have a flowering hedge – in which case, it's best to trim after blooming – September is ideal if you're wondering when to cut hedges," agrees Helena Jones. "The birds have finished nesting, and it’s early enough to avoid frost damage on freshly cut stems, but late enough that there won’t be much regrowth before winter."
Prune out any damaged or dead wood and thick growth to let in light and improve the structure of the plant, plus tidy up side shoots and any fresh growth that is spoiling the outline.
It's important to be up to speed with the legal height of hedging between neighbours too when tackling your pruning and cutting back.
8. Common box
Common box (Buxus sempervirens) is one of the most popular evergreens for topiary in landscaping ideas as it can easily be clipped into a range of shapes like balls and pyramids. It's also used for hedging, and in the same way as other evergreens like yew and cypress benefits from a good tidy-up in September.
It's simply a case of lightly cutting back any awkward or straggly stems that spoil the shape – using one of the best hedge trimmers will make light work of the task. This is an easy job as box is very springy and accommodating. Do this now and your topiary will look smart right through the winter months.
September is a good time to check for box blight disease. Although box blight can occur at any time of year, it’s especially common during autumn as it thrives in damp conditions. Look out for leaves that have a yellow or orange tinge, brown leaves on the ground round the plant, and a fine, white powder on the underside of leaves. Checking your plants regularly will help combat the disease.
Keeping your cutting tools in the best possible condition is key when pruning plants in September. Sharpening hedge trimmer blades will keep them working efficiently, and also remember the importance of cleaning your secateurs and pruning tools after use to prevent spreading diseases from one plant to the next.
If you're also going to be chopping wood to replenish your log store this month, our guide to sharpening an axe will come in useful to ensure you do it safely and efficiently.
