Very late flowering plants such as Sedum can be cut back in May (around the time of the ‘Chelsea Flower Show’) to produce shorter bushier plants that will then not require staking.
I find this makes the garden look much neater and borders appear fuller as a result.
Following exactly the same principals as ‘pinching’ Annuals, we remove the top of the plants (by about 1/3) which has ‘apical dominance’ and inhibits the development of the side shoots.
There is a hormone called Auxin in the tip of the plant causing this.
By removing the tip we remove the hormone and the side shoots are no longer inhibited and can grow strongly.
Note: The cut back plants will flower slightly later, but I find this then gives fresh looking flowers in the garden just as everything is beginning to look tired.
Sedum is also incredibly easy to propagate simply in water, full instructions is given in this video.
It’s important not to use this as a general rule, most perennials are not suitable for the Chelsea Chop and you will lose the flowers by cutting them back.
Other plants suitable for the the Chelsea Chop are as follows:
Anthemis tinctoria (Dyer’s Chamomile)
Echinacea purpurea (Purple Coneflower)
Phlox paniculata (Perennial Garden Phlox)
Sedum (upright, strong-growing forms such as ‘Autumn Joy’ (Herbstfreude))
Some plants such as hardy geraniums can be cut back AFTER flowering to encourage the chance of another flush of flowers in September. But really you are doing this to tidy the plants up which tend to flop after blooming.