I have to do a symbolism poem and I kinda wanna do it on Radishes. But I dont know what a Radish can be compared to.
Ahaha, as a classicist, this is probably the funniest question ever. xD
Radishes were used as a punishment in ancient Greece: any grown man found to have committed a sexual crime (there's some debate on which crime it was, exactly) got a radish stuck up his a** as determent.
Doesn't Luna have radish earrings in Harry Potter? So they'd represent her eccentricity there.
But the canon reason for them was that she just bought them because they were on sale. That's be thriftiness, no eccentricity.
You're confusing continuity with symbolism. There's a difference between reasons characters give so things make sense in verse and reasons the authors decide to include some detail that adds to a character, setting, etc.