"Gardenia" could have a nameday on Palm Sunday. Palm Sunday (the Sunday before Easter) is the day of flowers and willows (the names of the other trees also have a nameday).
I think this name is rather lovely, although the name would be most likely abbreviated to Dina/Dena or something like that, which is a shame because I think it's quite nice as it is. :)
I normally don't like many flower names because they sound so prissy, but this one is actually kind of cute. It sounds very pretty, but would make a better middle name.