In article , Steve Jackson
writes
Having cut off the now finished flower stems from my sweet william, is
it worth leaving the plant in situ for next year?

yes - I have a clump that have been going for several years.

I seem to remember that they are b1-annuals - is that right?

They are perennials which are treated as biennials. They do tend to
deteriorate after a few years, and they are straggly plants, so
gardeners appreciate being able to clear the ground and plant something
else.

--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm