September is a time of transition in the garden. While some plants are still enjoying the last of their summer growth, others are beginning to prepare for autumn dormancy.
It’s a useful month for a little pruning – but the key is knowing where to draw the line. Overgrown plants can be brought back into shape, shrubs and hedges tidied, and any dead, diseased or damaged branches removed before winter sets in.
There are also a few plants that can benefit from a timely trim. Pruning some late-flowering varieties now can encourage stronger growth and a better display next year, while certain fruit trees and soft-fruit plants benefit from pruning to help boost the following season’s crop.
But don’t be tempted to give everything a haircut. A hard prune in September can trigger a flush of tender new growth, which may not have time to harden before the cold weather arrives. You could also accidentally remove flower buds that have already formed for next year.
With that in mind, Royal Horticultural Society chief horticulturist, Guy Barter, recommends going easy with the secateurs in September. He also warns: ‘Large cuts will be slow to heal in autumn when disease spores can be abundant.’
So, before you head out into the garden, check what each plant actually needs — and remember that less is often more at this time of year. These are some of the plants Guy suggests focusing on:
1. Wisteria
Wisteria generally needs pruning twice a year to flower well – in late summer/early autumn and again in winter, around January or February. It’s an extremely vigorous plant and pruning just once a year can result in excessive leafy growth at the expense of flowers. The aim of pruning now is to keep it under control and encourage the formation of flower buds. ‘Cut back the long whippy shoots to five to six buds from their point of origin,’ advises Guy. ‘They will be shortened again in the winter pruning session.’
2. Rambling roses
A rambling rose produces long, vigorous stems and large clusters of flowers, usually in one spectacular flush. Prune after flowering, removing some of the oldest flowering stems and tying in the younger ones: ‘If there’s plenty of new growth, remove older shoots that have finished flowering and tie in the new ones to take their place,’ says Guy. ‘If strong new growth is lacking, remove dead or diseased shoots and leave the rest. Cut back old flowering shoots, complete with hips, by about two thirds.’
3. Raspberries and hybrid berries
These can be extremely vigorous, particularly hybrid berries such as loganberries, so pruning helps keep them manageable and improves airflow. ‘Cut out old canes that have finished fruiting, leaving strong ones to overwinter and carry next year’s crop,’ advises Guy. ‘If raspberry canes are crowded, remove the weaker ones, leaving about 15cm between each. Tie in long, whippy shoots of hybrid berries such as loganberries to prevent damage.’
4. Hedges
For an established hedge, think ‘tidy and shape’ rather than a hard chop. Remove unruly growth and maintain the desired shape, while avoiding heavy cuts. Guy’s advice:
Evergreen hedges: ‘There is still time to trim evergreen hedges so they will regrow just enough to look green and mossy all winter.’
Deciduous hedges: ‘Deciduous hedges can also be lightly trimmed but are unlikely to regrow much as they will be getting ready for leaf fall.’
5. Late-flowering shrubs
For many shrubs, September is about light shaping and removing dead or damaged growth, rather than a major prune. The aim is to avoid stimulating a lot of fresh growth just as temperatures are falling. ‘Cut off spent flowering branches from late-flowering shrubs such as buddleja and abelia to keep them looking graceful for winter,’ says Guy.
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