Give your plants the Chelsea chop if you want to keep them looking at their best all season. This handy pruning technique involves cutting back vigorous summer- and autumn-flowering perennials to create more compact plants, produce plentiful blooms and keep plants flowering for a longer period. The Chelsea chop is carried out between late May and early June around the time of the Chelsea Flower Show, which gives this well-known technique its name.
What happens if you don’t give perennials the Chelsea chop?
Floppy growth that needs staking
Some herbaceous plants develop quickly, producing long floppy growth that requires staking. These plants benefit from the Chelsea chop because it encourages compact, bushy growth that will be more upright and require less (or no) staking. Plants that have had the Chelsea chop are also more resilient to windrock and remain looking neater for longer.
Perennials that benefit most from being cut back to keep them compact include sunflowers (perennial varieties, not annuals), Helenium, Rudbeckia, Phlox and Aster (especially Symphyotrichum novi-belgii). If you’re not sure what species you have in your garden, look for vigorous perennials that put on fast growth with tall soft stems supporting heavy flowers. These are the most likely to suffer from problems such as becoming too leggy or flopping to one side later in the season. Giving them the Chelsea chop will keep them shorter and encourage the growth of side-shoots that will produce many more, smaller, flowers.
Unsightly bare centres
Other perennials grow quickly and fall outwards, leaving a bare centre that ruins the look of the plant and leaves all their flowers trailing along the ground. Sedum (now known as Hylotelephium) is one of the perennials most prone to this effect, and there are others too, such as Nepeta (especially Nepeta ‘Six Hills Giant’) that benefit from the Chelsea chop. When you cut back these plants, you’ll stimulate new growth that will produce bushier plants with less empty centres.
Disappointingly short flowering season
Giving plants the Chelsea chop can also help extend the flowering season. Either chop back some clumps of each species or cut down the front half of your clumps to create a variety of heights and blooms at different times. This method of pruning can delay the flowering period for four to six weeks, so you’ll have more colour in the garden and a far longer season of interest. Plants that benefit from this include Phlox paniculata, Monarda, Coreopsis and Leucanthemum x superbum.
How to do the Chelsea chop in 3 easy steps:
Where to cut Cut the stems of perennials, making sure your secateurs are clean and sharp before you begin. Make a sloping cut immediately above a leaf joint. How much to cut One way to do the Chelsea chop is to simply cut back all stems by a third (or by half for plants that grow quickly and have a tendency to flop.) Another option is to cut back the front section of the clump or cut some clumps and leave others. Which plants to cutVigorous perennials such as Solidago, Echinacea purpurea, Phlox paniculata and Campanula latifolia respond best to the Chelsea chop.
The Chelsea chop is a simple technique and there really isn’t much that can go wrong. Just give it a go and you’ll be surprised at how quickly your perennials respond with sturdy growth and masses of flowers throughout the summer and into autumn.
In this clip from BBC Gardeners' World, Monty Don explains the reasons behind this popular pruning technique: