How to Cut Back Perennials

Jo.Baker
Published on June 23rd 2019
102
A close up of a blue Geranium flower
As I type this, the sun is shining, and I'm sat staring out the window at my herbaceous perennial bed, eyeing up the hardy geranium which has sprawled out and is in desperate need of a hair cut.
An inherited variety (it came with the house) that looks a lot like G. 'Johnson's Blue', its stunning blue flowers have all finished and the plant is now using its energy to produce seeds.
The stretched out stems have collapsed over the top of nearby plants, and are providing shelter for pesky snails. These need to be gathered up and cut away close to the plant's base. By doing it now - in early summer - you provide the plant with plenty of time to grow a new lot of leaves and hopefully a second lot of flowers. Oriental poppies, Ornamental thistles, Dead nettles and Lady's mantle are all robust enough to be hard pruned in this way.
Tip Give the plant a good drink and a feed to help it get going again.
A close up of the flower of Stachys byzantina (Lambs Ear)
]*Stachys byzantine* Lamb's Ear can be cut back to produce mounds of fresh downy foliage.

Deadheading

Regular deadheading keeps plants looking vibrant and fresh by encouraging new growth and flowers. Florists frequently have the best plants because they will snip off flowers with as long a stem as possible for floral arrangements. I've been guilty of pinching off spent flowers as I've walked down the path leaving bare stems poking up. But for the best results, the trick is to cut the whole stem back to just above a leaf joint or the main stem, which is where new growth will hopefully emerge from.
This technique won't work with floribunda or rambling roses, whose flowers arrive in bunches. These have to have individual flowers snipped out until they're all finished and then the stem can be cut back.
A close up of pink rose flowers with green leaves
Flowers can be removed the moment they are past their best
Lupins and Foxgloves are both short-lived perennials, but their life span can be lengthened if they are prevented from diverting their energy into seed production. To do this, cut the stem away as soon as the flowers on the bottom half have faded. The plant will then concentrate its energy into new leaf production for the next year.
I find that Centaurea montana, the perennial cornflower, can get very leggy and without support, it will easily flop over, especially with the downpours we've had locally over the last couple of weeks. So I tend to cut the stems that have flowered back to the ground level as soon as possible, leaving plenty of leaf foliage to feed the plant.
A clump of Centranthus ruber in a garden setting.
Centranthus is a prolific seed producer, and cutting back flower heads the moment they have finished will prevent it from spreading, Photo by bambusparadise.de

Herbs

Another group of plants that can benefit from a cut are perennial herbs. You would typically give these a chop back in late May to stimulate tastier leafy growth. But if (like me) you haven't got round to it yet (the chives are buried under the geranium), don't worry, it's not too late to do it now. Cut them back to about 5 to 7cm (2 to 3") above ground. Avoid nitrogen-rich plant feeds, which will promote quick sappy flavourless growth. Instead, look for a slow release potash fertiliser which will encourage steady, strong re-growth.
Tip Mark the calendar to cut again around the end of August. Regular trims will prevent seed production and lengthen your supply of fresh herbs.
I can stare at it no longer. The border needs a proper going through. In three weeks time, we're opening the garden as part of our villages secret garden trail. A quick cut back, feed and a pray to the weather gods will hopefully produce a mound of leaves that gently spill over the edge of the flags, instead of the Crystal Maze-like challenge it currently is. Wish me luck.

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