The Chelsea chop (so called because it is usually carried out at the end of May, coinciding with the RHS Chelsea Flower Show) is a pruning method by which you limit the size and control the flowering season of many herbaceous plants.
Plants that respond well to the Chelsea chop include:
Sedum (upright, strong-growing forms such as 'Herbstfreude')
Many other summer- and autumn-flowering perennials can be treated similarly. The degree of cutting back is specific to each species but the closer to flowering time you prune, the greater the delay in flowering.
When to do the Chelsea chop
The cut-back is performed usually in late May or early June – i.e. around the time of the RHS Chelsea Flower Show.
How to carry out the Chelsea chop
Some herbaceous perennials can be cut down by as much as half with positive results;
- The plants are not so tall and leggy
- They need less staking
- The flowers are smaller but more numerous
This happens because the removal of the top shoots enables the sideshoots to branch out (the top shoots would normally inhibit the sideshoots by producing hormones in a process called apical dominance). Using this method, along with regular feeding and watering, ensures beds and borders look tidy throughout summer.
To carry out the Chelsea chop:
- Clumps of perennials can be literally be chopped back by one third to a half using shears or secateurs. This will delay the flowering until later in the summer and keep plants shorter and more compact
- If you have several clumps of one plant, try cutting back a few, but leaving others. This will prolong the overall flowering time
- Another method is to cut half the stems back at the front of the clump which will extend the season of flowering rather than delay it
You can read more about the Chelsea chop technique in the book The well-tended perennial garden: planting & pruning techniques by Tracy DiSabato-Aust (Timber Press 2006, ISBN 9780881928037).
This book is available from the RHS Bookshop and the Lindley Library.
There are few problems associated with this technique. However, some plants (not on the 'Suitable for' list above) do not respond well and you can lose the flowers for one year.