This weekend in London, the Royal Horticultural Society is hosting the epic Chelsea Flower Show. Held on the grounds of the Royal Chelsea Hospital since 1912, it’s become the most eminent garden show in the world. Members of the British royal family attend every year, along with 157,000 visitors from all over the world in 2018.
If you didn’t get a ticket this year, the show will simply have to serve as a reminder that it’s time for the “Chelsea Chop.” This refers to a pruning method that takes place in gardens across England in late May, coinciding with the dates of the show. I’ve been using this technique for years, ever since I read about it in Tracy DiSabato-Aust’s “The Well-Tended Perennial Garden,” but knew it as “cutting back.” It was described as the “Chelsea Chop” in the latest issue of Fine Gardening magazine, a term that is far more memorable and descriptive. I like the sound of it.
For me, The “Chelsea Chop” means grabbing a big pair of hedge clippers and quickly giving perennials like Achillea, Aconitum, Agastache, Artemisia, Aster, Campanula, Echinacea, Eutochium, Helenium, Helianthus, Hibiscus, Monarda, Nepeta, Persicaria, Phlox, Platycodon, Rudbeckia, Salvia and Veronica a radical haircut. I look for plants that have had a spring growth spurt and have reached about a third of their mature height. When I find one, I cut it back by a third or even a half.
This is not an exacting technique. I work quickly, and can get the whole job done in less than an hour. I make cleanup even faster by gathering all the clippings as I go, winding them into fist-sized bundles, and tucking them under the remaining foliage. This “mulch” will slowly decompose, adding nutrients to the soil.
We don’t live in England, but the late May timing is very similar for Yakima. I’m fairly bleary-eyed to the needs of my own garden until after I’ve recovered from the epic Master Gardener Plant Sale, which takes place the weekend before Mother’s Day. But I’ve learned the hard way that unless I give my own garden this timely maintenance, I’ll be sorry.
The “Chelsea Chop” keeps all those plants with a tendency to become tall and floppy from needing any support later on. If you grow perennials that like to sprawl and open up in the center, like ‘Walker’s Low’ catmint, the “Chop” will result in a bushier, sturdier plant. It’s all about disabling apical dominance. Removing the top-shoots enables the side-shoots to branch out, making the plant shorter and fuller.
In addition, some gardeners use the “Chelsea Chop” to delay bloom time. Try it if you want flowers to bloom for a particular date, such as a garden tour or party. Cutting perennials back like this before they flower will delay their eventual flowering by two to three weeks. The flowers that come later, though perhaps smaller, will be more abundant.
Perhaps you want to change the bloom time of a favorite plant so you won’t miss the show when you’re away on vacation, or to coordinate flowering among several different types of perennials in the same grouping.
You might be surprised to find that you like the look of very tall plants much better after they’ve been chopped since they’re now in better proportion to their neighbors in the garden.
A slightly different version of this pruning method can create a longer flowering period. In this case, “Chelsea Chop” only half the plant. These pruned stems will produce side shoots and then set buds that open two to three weeks later than the unpruned stems, which will bloom at the normal time. Remember to deadhead the first flush of flowers. If you don’t, those spent blossoms will signal to the plant to set seed, and it will not produce more flowers on the stems that you pruned back.
I’ve learned the hard way that not all perennials will respond positively to being chopped. If I remove the terminal flower buds on Acanthus, Arisaema, Aruncus, Crambe, Dictamnus, Filipendula, Geum, Hemerocallis, Heuchera, Hosta, Iris, Kniphofia, Lupinus, Papaver, or Stachys, they will not flower this year. Find a complete list of summer and autumn flowering perennials that do benefit in Tracy’s book.
I’ll admit that it takes some courage to perform this operation the very first time. Search “Chelsea Chop” on YouTube and find many charming videos of British gardeners showing us exactly how it’s done.