The Chelsea Chop
Some perennials respond well to what is known as the ‘Chelsea Chop’. I was going to say this isn’t some fashionable haircut, but in a way it is. At about the time of the Chelsea Flower Show many gardeners cut back the new growth on a number of summer- and autumn-flowering herbaceous perennials to limit the size of the plant, and to control when it flowers.
Some merciless, secateur-toting individuals raze the plants to the ground, leaving the poor crowns looking like skinheads. I’ve never been entirely convinced by this approach. I just can’t bring myself to be so ruthless; I prefer to give mine a ‘short back and sides’, leaving some healthy-looking stubble to grow away again.
So how much actually is a ‘short back and sides’? Well, you can reduce the entire plant by as much as half. This will result in plants that are more robust and shorter so they will require less staking. And by removing the growing tips, more side shoots will be produced which will in turn result in more flowers.
You could also select some stems at the front of the plant to have a haircut, leaving others at the back to grow away; a sort of ‘long back and short sides’ – this will give you a mixture of height and flowering time within the same plant.
In addition, if you have a drift of the same plant, you could give some a ‘short back and sides’ and leave others to let their 'hair' grow naturally.
Don't forget, when you do cut anything back, remember to snip just above a leaf joint – this will prevent die-back.
Not all perennials will respond to this type of pruning, however, but here are a few which received wisdom indicates seem to benefit from it:
Anthemis tinctoria (the picture is of A. tinctoria 'Wargrave')
Campanula (tall-growing ones – the picture is of C. lactiflora ‘Loddon Anna’)
Helenium (the picture is of H. ‘Kanaria’)
Hylotelephium - formerly Sedum (upright forms – the picture is of H. ‘Matrona’)
Nepeta (tall-growing ones – the picture is of our cat Phoebe bringing her very own catnip plant down to size!)
Phlox paniculata (the picture is of P. paniculata ‘Blue Paradise’)
Symphyotrichum - formerly Aster (tall-growing ones)
So sharpen those scissors - I mean secateurs - and get snipping!