Autumn is the season when it starts to dawn on you how much your plants have grown since those exciting early spring days that feel both an age ago and like last week. With lots of flowers finishing and fruits being harvested in autumn, whippy long growth and the gangly, top heavy shapes of plants become more obvious. Autumn is also a last chance to shape up evergreen hedges so they look sharp before cold weather arrives. Autumn is a time of upheaval, with many things leaving the garden for good, but it pays to not get too carried away with the pruning tools. A measured approach will pay off in the long run!
More pruning advice:
Why prune now
Tidying up Cornus kousa branches
One of the reasons to prune plants in autumn, especially towards the end of the season, is because most won’t put on any more new growth until spring, so the shape you have after pruning is the shape you will see for the next few months. This will show some plants off as features to give some structure to enjoy in winter while for other plants it will enable them to withstand the stormy weather to come. Other plants can be damaged if pruning is left until winter arrives, and some perennials will start to look rather tatty if old material is left exposed to the wintry elements and turns mushy. All in all, pruning in autumn will help many plants look better and fare well over winter.
What to prune now
Peacock butterfly on buddleja ‘Cotswold blue’
Any bush rose that has some rather long stems on it can be pruned now to create a more even shape, but more importantly to avoid it being unsettled by strong winds. Roses will have put on a lot of new growth since early in the year and sometimes very long, random stems appear and create a lop-sided plant. If long stems are bashed about by autumn gales, the plant can rock in the wind, disturbing the roots, and this can have a severe impact on how well the rose grows next year. Cut back overly long stems by up to half, cutting just above a leaf. Also trim off any very thin, spindly growth towards the base of the plant while you’ve got the secateurs handy because these growths won’t be able to support flowers well.
The stilt-like young stems of buddleia are rather brittle, even when they are reasonably thick, and they are prone to splitting in exposed sites at this time of year, if it’s very windy. Reducing the length of long stems by up to half will solve the problem. Make sure you make a clean cut. A good pair of sharp bypass loppers should do the trick for most stems although very thick ones might need a pruning saw. Cut a notch in either side of the branch before sawing through it, to stop the branch from tearing before you complete the job.
A well-shaped cornus (or even better a group of them) showing off brightly coloured stems is a real winter treat. They are one of few plants that can actually bring a bit of disappointment when they start to break into leaf in early spring, because it masks the beauty and simplicity of the bare stems. Now is a good time to trim off any stems that have started to turn brown and die back, cutting into clean wood. Also remove any stems spoiling the shape of the plant, and any thin straggly stems, to leave a perfectly shaped, strong-stemmed specimen to enjoy in all its colourful winter glory.
Unlike ramblers, which tend to have one big ‘all or nothing’ display of flowers in summer, repeat-flowering climbing roses keep blooming off and on through summer and into autumn. By the end of autumn though, it’s time for a tidy up. Any flowers that try and limp through winter are unlikely to be anything to get excited about. It is far better to get the plant in shape for next year. Start by shortening the length of long whippy shoots that have flowered this year, then tie them to their supports, using soft string. Shorten them by up to half, or more if you are growing them in a very tight space. Unless the plant has decorative hips, trim off any old flowerheads still intact, snipping them back to a leaf bud. Now is also a good time to completely cut off any stems that are not behaving and growing in the opposite direction to their supports, if they are too heavy to be easily tied in.
Pencil-thick prunings of roses, buddlejas, cornus, salix and currants can be used as hardwood cuttings to make more plants for free. Thick, healthy stems 20-30cm long that have been formed this year are the perfect candidates for successful rooting. Make a sloping cut at the top of a cutting, making a clean cut just above a bud. Then make a flat cut just below a pair of buds at the base of the cutting. Outside in a sheltered spot in the garden, push them into soil that has been dug over to loosen it up, leaving one third of the cutting showing above ground and placing one cutting every 15cm. Or push cuttings into deep pots (old rose or raspberry pots are ideal) filled with gritty compost.
Pruning Griselinia littoralis hedge in autumn
Evergreen hedges can be given a final light trim in early September to sharpen them up for winter. Make sure you use sharp pruning tools and disinfect them between different plants if you are pruning box hedges, to reduce the risk of fungal disease, and trim on a dry day. Avoid cutting conifers at this time of year though because pruning can lead to stems dying off and leaving bare patches in the middle of the plant that won’t grow back. Use bamboo canes and string to give you a guide if you’re looking to leave sharp edges but don’t trust your eye!
Cut back perennials like lupins before they turn soggy
Not all perennial plants form those idyllic, mesmerising sculptures that make the garden look arty in a hard winter frost. Some perennials just end up looking a mess once summer is over and they are best cut back. New England asters, lupins, leucanthemums and perennial lobelias are a few that are best trimmed rather than left in situ to go soggy. Cut back all the old flower stems to ground level and cut back leafy growth to just above it, once the plant has lost all its colour. Leave a little bit to remind you where the plants are, to help you plan next year’s display, in case you decide that some things will need moving in spring. This will also make it easier if you want to plant spring bulbs in between your perennials. Make sure you cut the stems at an angle so water can’t collect in hollow stems.
Shredded prunings make a good mulch for informal areas of the garden or excellent material for the compost heap. Resist the urge to shred stems that are thicker than the shredder can handle! These thick stems can be good for placing in a small pile at the bottom of a new compost heap to improve airflow, and reasonably thick prunings can be pushed in the soil to be used as markers to remind you of the position of plants that are about to go dormant, spring bulbs that have been recently planted, or areas of hardy annual seeds that have just been sown.
Blackberries in hedgerow
Blackberries and hybrid berries
Here’s a job that may require gloves and sleeves! It’s time to do battle with blackberries and their cousins (tayberries, loganberries, boysenberries) and remove the old growth to ensure that next year’s crop is a good one. Cut out all the stems that have fruited this year, cutting them right back to the base. If you’ve got some large plants, this is no task for the faint-hearted!
To avoid getting thorny stems in a complete tangle, cut them off in stages rather than cutting off long canes and then having to pull them out of the plant. Once all the old stems have been cut out, tie the new ones to their supports using soft string. Put the pruned material into a shredder, then compost it or place it on a bonfire. You could also place some of the cut stems over areas of bare soil, if you have a problem with cats pooing in your borders.
Summer raspberry canes can be pruned now, too. How do you know if you have summer raspberries or autumn raspberries? On summer raspberries, the canes will be looking tired, woody and won’t have fruit left on them. Summer raspberries fruit on canes that were produced in the previous year and by now they are looking old. Autumn raspberries will still be developing new fruits on fresh-looking canes. Cut summer fruiting raspberry canes back to ground level, making a cut flush with the soil surface so that you don’t leave a prickly stub. Once they are all removed completely at the base, you’ll be left with fresh, young canes that will crop next year. Tie those with strong, healthy growth into their supports (these will fruit next year) but remove any thin-looking canes that have sprung up this year and are growing close to them.
Prune ornamental trees like acers once they’ve lost autumn colour
Deciduous trees can be pruned once the best of their autumn leaf show has fallen to the ground. Most ornamental trees will form fine shapes without a lot of pruning and if you want the trees to look natural, it’s best not to be too ‘snip happy’. But now is the time to remove diseased or splintered stems, any branches that are rubbing against each other and low stems at the base of the trunk. Cut diseased and damaged growth back to clean, healthy wood, making a final cut just above a bud. Remove stems rubbing against others by cutting it out completely, cutting flush to where the stem began. Completely removing low branches on a tree to ‘lift’ the crown can open up planting opportunities underneath and also help show off the trunk, which is a good idea if it has attractive bark. Cut right back to the source to leave a smooth trunk. Only use sharp tools and clean the blades with disinfectant between cuts.