its a Cosmos. Its an annual so if you want them next year you need to sow seeds in the spring.

Cosmos bipinnatus. It's an annual.

IF they are like mine, you'll see volunteers popping up all over next spring.

yes I find that too Bathgate. they are lovely though.
I have the same 'problem' with Nigella, love in a mist. A lovely annual that I sowed seed back in 2001 and have a lovely display every year even though I have never sown another of its seeds since. In fact they are evenly spread through 2 beds now. :o)