Give it another flush (of flowers)
Around this time in mid-summer, the garden is in full swing and a vivid display of colour and form is hopefully on a show in your borders. However, plants that flower earlier in the season may now be starting to look a bit shabby.
Some plants can be cut hard back, moving all old foliage and spent flowers, to encourage a fresh flush of foliage and a good chance of a second flush of flowers too. It’s always worth a try with hardy geraniums, but some will not re-flower. Alchemilla mollis and Nepeta will generally re-flower but stay a bit smaller. This can also make space for any summer annuals or bedding, such as Cosmos or Pelargoniums.
If you can catch Delphiniums and Lupins just as the first flower spikes start to fade, cut them right down and give them a potassium-rich fertiliser such as tomato feed. This is what the Blackmore & Langdon, the Delphinium specialist at Chelsea told me is the key to amazing blooms all summer.
Deadheading is not something many people tend to bother with when it comes to herbaceous perennials, reserved for bedding plants and roses. If you can, however, many perennials will give a longer and more vivid display if spent flowers are regularly removed. This is very effective for Dahlia, Dianthus, Scabious, Knautia and plants in the aster family such as Anthemis, Helenium, Tanacetum and Gaillardia. With Penstemon I like to individually cut whole stems down to near the base as and when they finish flowering, so you have a steady arrival of new blooms. Alstroemeria will also keep flowering with dead-heading, but simply cutting off old flowers will not work. Instead, tug on individual flowered stems one at a time, to pluck them out from the crown of the plant below ground, a bit like harvesting rhubarb.
Another time when you may want to cut back fading flowerheads is on plants you don’t want to set seed. One reason to prevent seed forming is to help the plant retain that energy for better growth and flowering next year. Lupins and perennial foxgloves are a good example of this; they’ll produce heaps of costly seed at the expense of the longevity of the plant. Other perennials have the potential to self-seed to the point of weediness; such as Alchemilla molis, some hardy geraniums, and Knautia macedonica. Catching them before the seeds drop will save you a lot of weeding, unless of course you want some ‘volunteer’ plants to fill gaps.
The last group of plants to consider chopping are the earlier-flowering summer-dormant plants, with fading foliage as they go ‘back to sleep’ for another year. These are plants like oriental poppies, some Primula, some Dicentra, some Anemones, and some hardy geraniums. The dying leaves will be feeding the roots so don’t cut back anything too soon, but once things are more or less brown all old foliage can be removed and tender bedding used to fill the gap, if you like.