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Pruning in August with Frances Tophill

Frances cutting flowers in herbaceous border at West Dean Gardens

Pruning in August with Frances Tophill

BBC Gardeners' World Magazine

Published: Friday, 21 July 2023 at 1:29 pm

Frances Tophill shows you how to keep borders flowering into autumn and get magnolias in good shape

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It’s in the month of August when we generally get our most summery days, but also when the first chills of autumnal air begin to creep in. The mornings have a smattering of dew and the first leaves begin to turn crispy. As such, our gardens are often decidedly on the messy side and yet can be full of colour, as the late summer blooms start to come into their own.

August is all about abundance for us veg growers, with beans, tomatoes, courgettes, chillies and even sweetcorn being regularly harvested, and with constant deadheading, a continual display of flowers is also to be expected. As far as pruning goes, August can be a busy month, especially if your garden is full of evergreen hedges, as this is the peak time for topiary and clipping things like yew.

Summer pruning of water shoots can also fill the month, and certain fruit trees are especially prone to these, but so too are deciduous magnolias. It’s also your last chance to reduce the long, whippy shoots on wisteria to promote flowering next year and stop those tendrils taking over.

More pruning advice:

5 plant types to prune in summer
Your summer pruning jobs
Pruning in July with Frances Tophill

Plants to prune now

August pruning usually involves removing spent flowers, or shaping plants as growth begins to slow, so you won’t have dramatic regrowth before the colder season, when pruning can cause die-back.

Variegated evergreens

Remove shoots that have reverted back to pure green, before they grow to dominate the whole shrub.

Bay

Laurus nobilis should be pruned now, to shorten stems

Laurus nobilis should be pruned now. Use secateurs (long-handled if necessary) to shorten stems and avoid cut leaves, which will go brown.

Alchemilla mollis

Cut off untidy spent blooms and tatty leaves before watering

Cut off untidy spent blooms and tatty leaves from Lady's mantle, then water at the roots to encourage a fresh flush of velvety leaves.

Summer bedding

Deadhead zinnias and their bedfellows regularly

Deadhead zinnias and their bedfellows regularly – cut faded flowers back to a leaf joint from which another flower may grow.

Avoid pruning

Resist the urge to trim back ivy – let it produce its valuable nectar-rich flowers this autumn

Grapes: Although the fruit can be thinned and tendrils reduced, save the heavy pruning of grapes until winter, when the vine is fully dormant.
Ivy: This will flower soon and provide a late feast for pollinators. So if you want to bring ivy under control, wait until flowering has finished.
Roses: These should be pruned in winter or spring (except for ramblers). Pruning roses now will cause die-back that will need to be removed again after winter. If your rose produces hips, then stop deadheading soon to allow them to form.
Pelargoniums: Wait a month before pruning pelargoniums back if you want to propagate them – cuttings of these tender perennials root best in September.

Step-by-step: Pruning deciduous magnolias

Magnolias don’t need much pruning. They’re lovely trees with a beautiful form, if left to their own devices. Pruning them badly can often cause unsightly growth in unwanted places, which will mean you have to keep on pruning to try and correct the shape. Also, if pruned at the wrong time, they are prone to bleeding sap.

Although they’re slow growing, magnolias can eventually become large trees, so when planting in a modest garden choose a compact variety or prune considerately. In most instances, pruning magnolias just involves removal of water shoots, suckers and any dead, damaged or awkwardly growing branches. This is best done in late summer, otherwise the wounds can bleed a lot of sap.

Step 1

Use a clean saw to cut out any dead, dying or diseased branches, back to a sideshoot

Use a clean saw to cut out any dead, dying or diseased branches, back to a sideshoot. Also remove branches growing at odd angles. Don’t take off too much in any one year – come back and do more next year if necessary.

Step 2

Cut off any suckers sprouting from the base of the tree, as low down as possible

Cut off any suckers sprouting from the base of the tree, as low down as possible. These will often be small, so you should be able to use secateurs or loppers rather than a saw, which would risk damaging the main trunk.

Step 3

Gather up your prunings and put any smaller shoots and leaves straight on the compost heap

Gather up your prunings and put any smaller shoots and leaves straight on the compost heap. Thicker stems can either be seasoned for your fire, or put through a chipper or shredder before being added to the compost.

Return to your magnolia after a year to carry out a little more pruning if necessary. Pruning off too much at any one time can put the tree into shock, which can potentially lead to it dying or allow disease to take hold if the plant is weakened. Therefore, with any trees that don’t routinely need pruning, it’s always safest to just take off a little at a time and assess the plant’s health and shape the following year before continuing.

Also prune this way:

Prune these other trees in the same way as magnolias, although at different times of year.

Birch trees are best pruned in autumn. Never prune them in early spring when the sap is rising, as that can cause excessive sap loss, potentially weakening the plant.
Acers generally need little pruning, but if required, always do it during the dormant season, between November and January, to avoid sap bleeding from the cuts.

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