Sweet Williams - worth keeping?

Hi all

I grew Sweet Williams the first time from seed last year and they flowered brilliantly this year, they make great cut flowers with a good fragrance. Question is, is it worth keeping them for another year (I'm short of space)? They're biennials I think so in theory should not flower again, but the plants look healthy enough so I'll try. Has anyone else got more than one season from them?

Nick.

I have managed to eek out 3 years before they became too shabby, but it's far easier to buy new each year. Just be sure to not let them set seed