Hi Kate 1123 - the seeds were sown in seed tray in potting shed at beginning of May 2011, germinated within 2 weeks, pricked out in June and planted in ground in September 2011. I used to keep notes on when seeds were sown etc - had to abandon it as needed more time to prick out, pot on and then plant out - not to mention deadheading and weeding etc etc !!!
As mentioned, I'm going to let one or two self-seed this year but also thought I might try sowing some seed in September and see what happens. The ones in the garden will be going to seed soon so, seems to me, seed could be sown now, perhaps ?
Hope this is helpful and not too confusing !! 