From wisteria and roses to summer perennials, a plethora of plants benefit from a timely trim at this time of year.
So many, in fact, that you may be tempted to cut back more than just a few varieties and, before you know it, you find yourself in a full-blown pruning frenzy.
That's a mistake, however. Growing and maintenance schedules differ heavily from plant to plant and, while there's plenty to prune in July and August, many flowering favourites should strictly be left alone. Cut them back at the wrong time and you could removing developing buds that would otherwise bloom later this season or next spring.
Knowing what to prune is important, but knowing what not to prune is just as essential. Below, we've rounded up six flowering plants that are best left off your late-summer trimming list.
1. Forsythia
Do you have one of these sunshine-yellow shrubs growing in your garden? Resist the urge to reach for the secateurs, or you could be left with bare branches come spring.
"The plant blooms on old wood and by trimming in late summer you could be removing the following year's flower buds," explains Richard Barker of LBS Horticulture. "If these flower buds are removed, you will have a flowerless shrub in springtime."
The best time to prune forsythia is ideally just after it finishes flowering, which is usually in late spring.
Richard adds: "If you have a heavily overgrown plant, you can remove dead, diseased or damaged branches at any time of the year, but do not shape or shear the plant."
2. Lilac
Lilacs are another shrub that's best left alone in late summer. They start producing next year's flower buds immediately after their current flowers fade, so trimming them now could mean sacrificing next year's spring's display.
"By pruning in late summer you risk cutting off these buds, resulting in no flowers in the following spring," says Richard. "The only exception to this is deadheading, as this can stop the plant from using its energy to produce seeds. Only cut bare stems carrying seed capsules, and do not touch any green foliage."
3. Azaleas
Azaleas put on a spectacular show in spring and preserving that display means resisting the urge to prune now.
"They set their flower buds for spring around mid to late summer," explains Richard. "If these buds are removed, the plant will only produce green leaves and no flowers the following year."
While light deadheading is fine throughout the growing season, any substantial pruning should have been done after flowering in spring.
4. Rhododendrons
Like azaleas, rhododendrons are spring-flowering shrubs that should never be cut back in late summer. "They will be forming their flower buds for next spring and you risk cutting these off," says Richard.
Pruning now doesn't just mean depriving yourself of a dazzling display; it can actively weaken the plant.
"Pruning will also encourage new growth, and any branches that grow in summer will not have enough time to harden off before the colder temperatures in autumn and winter, making them more vulnerable to frost damage."
5. Asters
As autumn garden favourites, asters are only just beginning to prepare for their main display. "If you cut them back in late summer, you potentially remove developing flower buds and will have fewer flowers when they do begin to bloom," warns Richard.
"It is best to focus on deadheading faded flowers as they appear, or wait until the first hard frosts to prune the plant back to the ground."
6. Chrysanthemums
Another classic autumn bloomer, chrysanthemums are also busy setting their flowering buds at this time of year. Prune them now, you risk losing vital late-season colour.
"If chrysanthemums are cut back, this can delay or ruin the blooming of the plant in autumn," Richard adds.
Instead, focus on watering and feeding to help this beautiful late-season bloomer produce a vibrant display, and save any major pruning until after flowering has finished or in early spring, depending on the variety.
Summer gardening edit
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Wanda Sachs is the Multiplatform Writer for Country Living and House Beautiful, exploring the latest in gardening, wildlife and sustainable living alongside interiors and property. She is particularly interested in human-interest stories, the intersection of design and pop culture, and the evolving relationship between urban and rural life. Previously, she served as Associate Editor at The Berliner in Berlin, where she reported on culture and fashion. Wanda studied English and German at the Goethe University Frankfurt and Exeter University.
