Christina Websell wrote:
Something that looks like a potato when it comes up, one of the nightshades.

I have a huge nightshade growing in a basket in the front. I have no idea
where it came from, but it's doing really well!

My next door neighbour and I both have Mysterious campanula, that look identical
(very short, same colour!) and no idea where they came from.

The biggest 'weed' on the allotment this year is the parsnips, which were seeded
from the next plot and have totally taken over the onion patch. I didn't want
to pull them up, but they've become a bit of a slug/snail haven. (nto that there
are many slug-free areas!)