There should be a lady in the Pokemon center in Lacunosa Town who talks about the Gracienda flower. I'm sure that if you have Shaymin with you, she will give you the Gracienda flower. You might have to do this during the time that the Gracienda works, and Shaymin might have to be first in the party. (I know that this has been said in another question, but at least you can't vote me down for lack of info.