Every year, right around the last week of May, my Instagram feed fills up with garden design inspiration from the Chelsea Flower Show that takes place in London.
I don’t live in the UK and I’ve never been to the show (though it is on my bucket list), but I still get giddy at looking at photos for inspiration and following the different themes each year. (This year it’s all about resilient gardening, bringing wildflowers back into focus and dog-friendly gardens.)
But the Chelsea Flower Show is also a good reminder that it’s time to pick up my secateurs again, for the first time after the flurry of early spring pruning, and get to work on some of the “prune in June” gang.
This pruning method is called the Chelsea chop, since it coincides with the timing of the flower show.
Let me tell you a bit more about the Chelsea chop – and what you can prune in June – and you can assess whether there are plants in your garden that could benefit from being taken down a peg or two.
Does it really make sense to prune in June?
Pruning perennials in June may seem a bit counterintuitive. We know we need to prune in spring for rejuvenation and in the fall for plants that generally don’t overwinter well in their full attire.
But what’s the point of pruning plants right when they’re hitting their growth stride?
What are we trying to achieve with the Chelsea chop?
We have two goals, both of them aesthetic.
First of all, this pruning method prevents plants from getting too leggy by the end of summer.
It keeps the plants compact by the end of the season and encourages branching. This means that I get to skip one of the only true gardening chores, in my book: staking! I won’t have to run around figuring out how to anchor tall perennials to keep them upright in July. Which is especially a headache on windy or rainy days.
Have a look at the salvia below, that completely toppled over its neighbors after a storm. This is a problem that mostly goes away when we prune for compact plants.
Our second goal is to interfere with the timing of flowering. By taking off the dominant top growth (which would have eventually flowered), we’re encouraging the lower parts of the plant to start producing flower buds. So in effect, we will get more flowers, but later in the season.
How much later depends on the plant and on what kind of climate and weather we’re gardening in. Generally, this late-spring/early-summer pruning may delay flowering anywhere from three to six weeks, on average.
There’s one thing I should mention here though: even though there will be more flowers, they will likely be smaller than those of the dominant growth that we’ve cut off.
What’s the best time to go out in the garden and do the Chelsea chop?
The best time to do this is in late May to early June. If you’re in a milder and warmer climate, or if you’ve had a mild spring but with plenty of rain, your plants may be ready for the Chelsea chop sooner (mid-May).
If you’re in a colder zone where it takes a bit longer to jumpstart growth, then early June might be the better timing for your garden.
The key is to do the Chelsea chop when the plants are in active, vigorous growth.
And another tip I want to warn you about: skip the Chelsea chop if your plants are already stressed. For example, if you’ve been having a dry season so far and your perennials are struggling, then it’s better not to overtax them this year. There’s always next year.
How much should I prune in June?
I’ve seen advice that includes anywhere between taking off the top third of the plant, or a half, or even two thirds. I must confess I’ve never been brave enough to cut off two thirds. (With one notable exception, which is oregano.)
I generally stick to the safe rule of cutting off the top third. But my choice also depends on the plant. For some (such as anise hyssop), there’s plenty there to allow me to cut off half and get away with it. For others, such as autumn sedum, I’m more cautious.
The first time I did it, I was a bit nervous. It didn’t make sense to me to prune perfectly good plant material. So I only pruned one out of the two plants, just to have a control group. Not only did nothing bad happen to the plant that I pruned back in June (a chrysanthemum), but it still bloomed and did indeed stay more compact through mid- to late fall.
Just like with any other kind of pruning, cut right above a set of leaf nodes.
An in-between method, if you’re not feeling brave.
If you’re still a bit squeamish about pruning plants that are actively growing, here’s another idea that works well. You can simply cut back the outer stems, leaving the stems towards the center growing as they are. Think of it as a layered haircut, if you will.
In response, the center will bloom first (as it normally would), while the edges will follow a few weeks later. This will prolong the pruning season not just for you, but for the pollinators in your garden as well.
You can even experiment with a single plant and take photos throughout the summer to see the difference. You’ll see that it works and hopefully muster up the courage to do it more next year.
What plants can we prune in June using the Chelsea chop method?
This method works well if we apply it to herbaceous perennials that have a compact growing pattern. It’s important to note that these are summer and fall-blooming perennials, not something that is already on its way out.
I’ve put together a list of the most popular perennials that respond well to this pruning technique:
Golden rod (Solidago)
Salvia (Salvia nemorosa)
Cone flower (Echinaceea)
Asters (Symphyotrichum)
Sneezeweed (Helenium)
Coreopsis
Tall stonecrop (Hylotelephium)
Bell flower (Campanula)
Joe Pye Weed (Eutrochium)
Bee balm (Monarda)
Yarrow (Achillea)
Beard tongue (Penstemon)
Catmint (Nepeta cataria)
Tall verbena (Verbena bonariensis)
Oregano
Tall phlox (Phlox paniculata)
Perennial sunflower (Helianthus angustifolius)
Are there any plants that we shouldn’t use the Chelsea chop on?
You may have noticed that some summer popular bloomers are absent from my list. That’s because there are some plant categories that we shouldn’t even think about pruning in June.
Don’t prune annuals like this.
Annuals have a different growth pattern than perennials. They are only meant to flower once, after which they will start going to seed. You can deadhead annuals to keep them looking fresher for longer, but don’t use the Chelsea chop on them.
We should be extra careful here to make sure that the cultivars that we’re cutting are indeed perennial. Because there are ornamentals that have both a perennial and an annual version, such as the sunflowers from the list above.
Don’t prune shrubs like this.
Shrubs, such as lilac, hydrangea and viburnum, have a different growing pattern. They formed this year’s flowers last year. If you remove those stems, you’ll not get more flowers this year.
Don’t prune plants that send up a single shoot like this.
As I mentioned before, the perennials that do well after this prune are the ones with a compact growth pattern. Think lots of stems with lots of blooms. We can’t really use this method on plants that send up a single shoot, such as foxgloves, oriental poppies, irises, sea holly or lupines.
Overall, I think a counterintuitive pruning method such as the Chelsea chop is easy to learn but hard to convince ourselves to put into practice.
But if you promise me you’ll try it once, even if just on a single perennial, I’ll promise you that it will work out. You’ll get a more compact ornamental full of beautiful little flowers. And a whole lot of courage to experiment and learn new things in the garden.