They are really better treated as biennials even though they are short lived perennials. I have just been removing all our finished ones and will replace them with new seedlings in September for next years flowers.
You can cut them down and they do regrow, but to my mind never as good as new plants.

Agree, it has seen its better days. Replace it with something else and start up some new seeds. 2 years only, 3 for the mighty plant.

If it's their 1st year,I would cut them right down to where you can see new growth,and it's so easy to take cuttings from the pieces you cut off. I've just done that with mine,and cuttings were potted on yesterday.You will still get some nice Wallflowers from the old ones next year,as well as plenty of new plants.Mine have been lovely,and it's their third and last year..good luck,whatever you decide to do..

Many thanks, I'll take cuttings as its now in it's 3 Yr and was not as lovely as last year

.I have just pulled my old ones up only today,,so looking forward to my cuttings taking their place :o)I hope yours do well for you too.:o)