The meaning of the title might have to do with the epigraph that Ngugi wa Thiong’o uses. Remember, an epigraph is a quote or excerpt at the beginning of a book. Usually, the epigraph is not unrelated to the overall meaning of the book. In Petals of Blood, Thiong’o includes an epigraph composed of three stanzas from Derek Walcott’s poem “The Swamp.”
In the poem, the phrase “Petals of blood” appears. The image—bloody petals—seems to be in keeping with the overall theme of Walcott's stanzas. Throughout the stanzas, Walcott attaches natural, organic elements to a fearful quality, which creates an unsettling, odious juxtaposition and atmosphere.
Perhaps the meaning of that juxtaposition carries over to Thiong’o’s own narrative. In Thiong’o’s novel, the contrast is between Ilmorog and Nairobi, with Ilmorog playing the role of nature (the relatively harmonious, unthreatening element) and Nairobi playing the part of the odious predator.
Then again, perhaps the meaning of the title is not so simple. By combining petals with blood, maybe Thiong’o is commenting on the relationship between beauty (the petals) and bad behavior (the blood) or innocence and exploitation. It’s possible that the meaning is not so binary. Perhaps, as Walcott’s poem suggests, nature and violence have more in common than some might presume.
Near the end, Wanja tires to explain her involvement with sex work. She states (more than once), “You eat or you are eaten.” That quote could reveal a lot about the meaning of the title. It suggests that almost anything—including petals on a flower—is capable of playing the predator and drawing blood.