Thank you so much to all - I think it is definitely this willow herb. I remember this 'plant' now with light purple flowers last year. I must have been unsure if it was something I'd planted (I'm still filling my relatively newly landscaped garden) and let it flower last year. Now I have about 100 of them! To be weeded asap.
I think I need a database of 'what my bought flowers look like when tiny'!
Don't think they are Chinese Lanterns, look very like Sweet Williams.
I do have some Sweet Williams on the go that I've grown from seed but these are different. I'm pretty sure they are willow herb (weed) as many have mentioned. They are about to get weeded!
Posts
I live in west central Scotland - not where that photo is...
I think I need a database of 'what my bought flowers look like when tiny'!