How long ago did it flower. The seed needs to be mature but not turned brown. It doesn't matter about wet, you're sowing the seed not storing it. If you have enough, do a few every couple of weeks, some of them are bound to be right.
I hate it
and the rest of the spiraeas
I keep throwing out lumps of that big pink one and its descendants. It's pretty but flops far too much for its flowerworthiness. (is that a word or did I just invent it?)
the manure won't have been good for it, those plants that like well drained soil don't appreciate that. and we've had a lot of rain here, that's not so good either.
an oxonianum hybrid, one of many, would be my guess
I don't think it's a teasel. Ceres asked the question re the spines but it hasn't been answered.
vialii is a species, no problem with seeding true with that one.
It's not just the F1 hybrids that don't come true, none of the hybrids or culltivars will.
It might be Canadian Fleabane, Conyza canadensis
Still a weed though
They are generally smaller than biennis though it varies with soil.