Sweet Flag
SzélsőFa asked me "onions in the bathtub? for what reason? decoration? "
Now I answer this is not onions. That is Sweet Flag.
When it is May 5 , we take a bath with Sweer Flag. May 5 is Children's Day (boys day). We celebrate their happiness. So we take a bath with Sweer flag, they become to be health more.

When we went to Shikoku, I took this picture. When it is May 5, parents who have boys decorate carp-shaped flags.

These are Japanese iris. My uncre, who lives in Nara, sent pictures. I misunderstood sweet flag and iris are same plants. My uncle adviced plants in the bath is defferent of iris by e-mail.

Thank you for helping!!