Claudia and Frieda associate marigolds with the safety and well-being of Pecola's baby. They believe that if the marigolds they have planted grow, then Pecola's baby will be all right.
Another view, is that marigolds are strong and resilient. This strong resilient flower represents the African-Americans that survived over 400 years of the cultural genocide committed by the whites. The black people of America survived the middle-passage, survived slavery, and survived every other bought of oppression that occurred in America.