Symbolism, Imagery, Allegory
This is just a little symbol in the book, but we think it's a particularly cool one, so we wanted to be sure to include it. When it's time for Parvana to leave Afghanistan, she wants to say goodbye to the Window Woman (who's a symbol in her own right, so be sure to read her analysis). But since they've never spoken—and the woman has to stay hidden indoors—the way Parvana does so is by planting flowers in the place she usually sets up her blanket, right below the Woman's window.
Pro tip: Anytime someone plants something in a book, you probably want to pay attention to whether or not it happens around the same time as an important change. For our purposes with Parvana, this is definitely true—she's preparing to leave Afghanistan, the country she's been born and raised in, to journey to Pakistan with her Father in hopes of finding the rest of their family. And that, Shmoopsters, is about as big of a change as someone can experience.
The thing is, though, that this isn't the only change the flowers Parvana plants represent. Remember how scared and lonely she felt when she first started going to the marketplace? Her father had just been kidnapped from her family's home, her mother and siblings were depending on her to make money to support them, and she was disguised as a boy in hopes of not getting caught by the Taliban. And though it's not like Parvana never feels fear anymore by the time she plants the flowers, she has done some serious growing up during her time in the market—and the flowers represent this change, too.
When Parvana plants the flowers, the townspeople make fun of her, saying the flowers have "no nutrients" (15.52) and "will be trampled" (15.53)—but this doesn't stop her. They might have said the very same things about Parvana, after all, but she managed to grow and survive on the mean streets of Kabul—and perhaps her flowers will too after she's gone.
A stranger comes by and says that "Afghans love beautiful things" but they forget about the beauty in the midst of "so much ugliness" (15.55). The Window Woman and her gift of friendship have been a bit of beauty in the midst of a challenging and often ugly chapter in Parvana's life, so they are the perfect gesture of gratitude for her to leave behind for her mysterious friend.