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I have this plant growing in the garden everywhere but don't know it so don't know what it might be telling about the soil. Any ideas?

Looks like groundsel to me.
It's a very common garden weed, so I don't think it tells you anything about your soil.
Not a good idea to let it seed though, it has seeds like a dandelion that spread everywhere on a breezy day.

I always leave some of it as it is one of the foodstuffs for the cinnabar moth caterpillar. They are very pretty red and black daytime flying moths and there have been loads around here recently.

Definitely groundsel.
I didn't know cinnabar moth caterpillars ate groundsel, though it was just ragwort. I will leave some groundsel untouched from now on!

Yes they like both - and it's easy to get rid of groundsel that's self seeded as it pulls up easily.

Thank you all for the replies. I appreciate them.