could be a Tradescantia but going by the intense blue colour it could be Commelina, day flower or widow's tears.

its very pretty either way.

Thanks Seaburngirl, the leaves made me think tradescantia
but not the flower. They are fully open now but seem to close in full sun.

Commelina for sure.

As Owdboggy says, Commelina comunis. Called dayflower or widow's tears. It's a terrible, beautiful weed where I live, but I don't know what it does in colder climates.

Rarely survived a winter for me. Grew it as a hardy annual.

I had it come through for 3 yrs then lost it. if I remember correctly I grew it from seed. I might treat myself to some more and see if I can keep it but growing it as an annual is a brilliant idea. It is such a lovely clean blue too.

Thank you all so much for your replies. It just appeared this year so I'll see if it survives the winter. I could collect seed for you Seaburngirl if you wish - well I could try - you would need to advise me on collecting and storing though as my growing from seed of anything is very hit and miss.

Thank you all so much for your replies. It appeared from nowhere this year so it will be interesting to see if it survives the winter. Sorry I seem to have sent this twice and don't know how to cancel it.

Since I've done this more times than I want to admit to, I've found that if you use the edit comment fuction to erase all the text, then the resulting empty box eventually disappears.