Symbolism, Imagery, Allegory
This novel's preoccupation with flowers is hardly subtle. Within the first few pages, we're introduced to a heroine named Lily and another main character named Rosaleen, and that is only the tip of the iceberg (or stamen).
In addition to being associated with characters, flowery imagery can show up in surprising places in Lily's universe. Describing the moments when she feels her mother's loss most painfully, Lily recalls:
But you know when I missed her the most? The day I was twelve and woke up with the rose-petal stain on my panties. I was so proud of that flower and didn't have a soul to show it to except Rosaleen. (1.87)
With references to the stain as both "rose-petal"-colored and a "flower," this moment is an early big clue that flowers and femininity are close comrades in this book.
Later, Lily makes up a fake grandmother named "Rose," and she also discovers a William Blake poem called "The Sick Rose" in her mother's poetry book. There are even a few lilies thrown in there—for example, when she is thumbing through August's books, she finds a picture of Gabriel giving the Virgin Mary a lily.
So, stringing together these references is all well and good, but what do they mean? Well, you may have noticed that they frequently coincide with references to maternal figures (e.g., Lily's mom, the Virgin Mary, and even this fictional grandmother), so flowers and flowering seems to have something to do with highlighting the importance of maternal bonds. To support that point, we'll throw in one of the final references to flowering in the novel, which appears just after T. Ray has allowed Lily to stay with August and the other Daughters. Thinking of that moment, Lily writes:
I still tell myself that when he drove away that day, he wasn't saying good riddance; he was saying, ["]Oh, Lily, you're better off there in that house of colored women. You never would've flowered with me like you will with them.["] (14.216)
In essence, Lily's ability to finally "flower" in the sunlight of maternal care represents her happy ending.