We don't know how big the bigger leaf is.
I can see the likeness to milkweed seeds.
https://www.google.co.uk/searc...
When seeds have been soaked and swollen they will look a little different.
You said "The seeds are tiny, brown, with papery sides". How tiny is tiny? Can you give a measurement in millimetres?
A photo of a whole seed not covered at all by compost might help, but it's going to be easier when we can see the true leaves. Do you have any of the dry seeds?
