It looks like an elm seedling, which would make sense if it is in all the places you say (elms throw seeds everywhere!). I get many showing up from my lacebark, but when they occur in the lawn just mowing seems to eventually eliminate them. As far as those in pots you will have to pull, but doing it when they are small is usually a one-time deal because it is easy to get the whole root.

Not that they were all seeded at the same time but more like they are all responding to the same conditions for germination.

Though it's interesting why they would be inside your bed already, unless the wind moved some there recently or you used some of your native soil in your bed.