Give these garden favourites a trim now to encourage fresh growth and keep them looking their best
August is a good time to give certain perennial plants a tidy-up. Once their first flush of flowers has faded, cutting them back can remove tired foliage, prevent unwanted self-seeding and, in some cases, encourage a fresh flush of blooms before autumn.
Not every perennial needs pruning at this time of year, but these five will all benefit from being cut back before the end of August.
These pretty purple flowers can start to look tired and leggy after their first flush of flowers, making August a good time to cut them back. A hard prune can help remove spent foliage and encourage the plant to produce fresh growth.
‘Hardy geraniums should be cut back hard to a few inches above the plant's base after their first flush of flowers begins to die off,’ explains Richard Barker, horticultural expert and commercial director of LBS Horticulture.
When pruning, take care not to cut into the woody crown at the base of the plant. Then, remove the clippings and any fallen leaves afterwards, as this helps improve air circulation around the crown.
Read more: What to do with hardy geraniums after flowering for more blooms next year
Luscious and green, lady’s mantle can become particularly untidy in August, especially after flowering, usually with floppy stems and brown or tired foliage. Cutting it back at the right time can encourage fresh growth, while also preventing it from spreading too freely around the garden.
‘Faded stems should be cut back after the plant has finished flowering, and it is best to do this before the seeds ripen so the plant does not self-seed,’ advises Richard.
If the plant has become particularly straggly, the stems can be cut back down to the ground to encourage new stems to grow. Once you’re done, leave the crown unobstructed so that new growth has plenty of space to emerge.
This is another perennial that can become leggy by August, particularly after its first flush of flowers has faded.
‘Trim the plant to just above the first set of healthy leaves or lower buds, and remove clippings from the base of the plant to keep air circulating around the crown,’ Richard explains.
Rather than simply removing the flower heads, trim back the stems enough to encourage fresh growth from the lower part of the plant. ‘Cutting catmint back can trigger the plant to produce a second wave of flowers before the first frosts,’ Richard adds.
Once their first summer flowers have faded, delphiniums can be cut back in August to encourage the possibility of another flush of blooms.
‘Cut the spent flower stalks back to around two inches above the ground, or just above the foliage at the base of the plant,’ explains Richard. ‘Remove any dead or yellowing leaves at the same time to keep the plant looking tidy and reduce congestion.
After pruning, it’s also a good idea to use a balanced fertiliser, as this can support new flowers once fresh growth appears. Just avoid overdoing the feeding late in the season – the aim is to support healthy regrowth, rather than encourage soft, weak growth.
Read more: What to do with delphiniums after flowering for a second display later this summer
If yarrow has started to become leggy or is beginning to set seed, it’s time to give it a trim. This will encourage the plant to produce new stems instead of seeds.
‘Do this by at least halfway towards the basal foliage, taking care not to cut into the crown or remove the main basal leaves,’ says Richard.
This will give the plant a much tidier appearance and can encourage new growth from the base. Follow up with thorough watering for strong recovery.
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