Here is something I did not invent, but did with Scouts. Took 2 small panes of glass and placed cotton between them. (4 inch x 4 inch). Placed into container 2 inches deep in water. Sprinkled seeds on top of exposed cotton. Watched seeds develop. Scouts were able to see progress of roots and foliage.
I'm not suggesting going that elaborate here. Taking a cotton ball and placing it into a jar lid with water. Sprinkle suspect seeds onto it . In no time germination will be visible. Those seeds can then be transferred into soil.
Takes out the guesswork if directly planted int soil. Is it my plant or a fly by weed seed.