The pic could be cosmos foliage - it's hard to tell with the ends weighted
down with water. I suppose it's possible that some seeds survived
underground for several years and germinated when the soil was disturbed,
although I wouldn't normally think of cosmos seeds as being that persistent.
(Usually hard-coated seeds like grains and beans seem to have a longer
"shelf-life".) There are a few other plants with very fine thread-like
foliage, including nigella. Have you ever planted that? (Just thinking out
lout).
"Diane" OK, here's the foliage,
anyone?

http://old-homes.net/pix/ours/flowers03/IMG_1040.jpg

Thanks!

Diane