I don't think it's tansy, the leaves on mine aren't as fine as that. The foliage looks like cosmos or nigella but I don't think it's either of those. The buds(?) don't look right. I'm intrigued now.
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LiriodendronScariff, County Clare, IrelandPosts: 7,872
Might it be pineapple weed - matricaria discoidea? If it is, the foliage will have a distinctive smell.
"The one who plants trees, knowing that he will never sit in their shade, has at least started to understand the meaning of life." Rabindranath Tagore
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https://www.rhs.org.uk/Plants/17990/Tanacetum-vulgare/Details